Coolant Leak

[10-4onthe79]

Good Morning,

Well, it's been an interesting few years. It looks like the site had a major issue as well, which is disappointing to see. I cannot begin to list all of the items this site has helped me with as I was tearing my car apart and assembling everything again.

I have a coolant leak that I thought originally was the hose going into the thermostat housing. When it would get cold out, there would be antifreeze at the top of the water pump and on the valley pan. I am unable to locate this leak as I'm pretty sure it only happens when the car is by itself at 2AM. It seems to be getting worse. I was going to drain the coolant, change the water pump and thermostat housing, but I don't want to tear everything off if this is something simple. I would post pics but wasn't sure the procedure for that on this site anymore now that photo bucket has changed. I pressure tested the system and it seems to hold pressure just fine. It never overheats when driving. I also noticed a few drops of coolant on the thermostat housing bolt after driving, but it may have splashed up? It WILL leave a puddle of coolant on the ground (SOMETIMES) but only after it sits overnight+ and usually when it gets cold outside. If I drive it and park it, nothing. I'm very confused. Looking for a place to start if anyone has any ideas? I probably should also add that the engine is a Pontiac 400 that was rebuilt in 2013. They used the original water pump and the engine has about 2,000 miles on it. Thanks for any input.

[tinpusher]

Had the same issue. I took the thermostat housing off, put it on my bench sander to start with a totally flat surface and new quality gasket And light on the sealant. After driving it and letting it sit , I noticed antifreeze, removed it again to throughly inspect it  and noticed a hairline crack in the housing along the casting line. Got a new one from Oreillys...no issues since.

[10-4onthe79]

Awesome. Thanks! I will give that a shot first and hope that fixes the problem. 

[nUcLeArEnVoY]

Good Morning,

Well, it's been an interesting few years. It looks like the site had a major issue as well, which is disappointing to see. I cannot begin to list all of the items this site has helped me with as I was tearing my car apart and assembling everything again.

I have a coolant leak that I thought originally was the hose going into the thermostat housing. When it would get cold out, there would be antifreeze at the top of the water pump and on the valley pan. I am unable to locate this leak as I'm pretty sure it only happens when the car is by itself at 2AM. It seems to be getting worse. I was going to drain the coolant, change the water pump and thermostat housing, but I don't want to tear everything off if this is something simple. I would post pics but wasn't sure the procedure for that on this site anymore now that photo bucket has changed. I pressure tested the system and it seems to hold pressure just fine. It never overheats when driving. I also noticed a few drops of coolant on the thermostat housing bolt after driving, but it may have splashed up? It WILL leave a puddle of coolant on the ground (SOMETIMES) but only after it sits overnight+ and usually when it gets cold outside. If I drive it and park it, nothing. I'm very confused. Looking for a place to start if anyone has any ideas? I probably should also add that the engine is a Pontiac 400 that was rebuilt in 2013. They used the original water pump and the engine has about 2,000 miles on it. Thanks for any input.

I had a coolant leak at my thermostat housing after I put on a new gasket during an intake gasket replacement. It only leaked when under pressure by the water pump (aka car was running). You'd find a puddle in the depression behind the valley pan flange at the front, and when driving it would run all the way back along the valley pan to the distributor mounting area, making me think I had an oil leak at the distributor mount or even rear valley pan (it's not painted back there, so hard to tell the color of the liquid).

I removed the stat housing, made sure it was flat, and used a Butler Performance gasket with a small thin film of RTV... still leaked.

The best thermostat housings are the factory types that have a sealing ring cast into the mounting surface. Pontiac used two types with the same part number #489869. The ones that originally came on 78 and 79 400's had the part number cast into the top of the housing in a capsule shaped inset, and feature a sealing ring on the mating surface (like this one: https://www.ebay.com/itm/392273788826?epid=1623824528&hash=item5b5556ff9a:g:lj8AAOSwroJchDux). The rest of the housings that share the same part number have the number stamped along the flange and have a flat mating surface. The ones you'll mostly find used and the ones that are repro'd are the perfectly flat ones. It's tough to find the ones with the sealing ring in good condition that aren't pitted to heck. However, there is another thermostat housing that GM produced in the 80's for base Firebirds and GM Astro Vans that is pretty much identical to the one's that came on our 400's with the sealing ring. Part number is 10021153. It works 100%, only difference is that instead of the cast in part number, it has a 1" raised section at the top to serve as a stopping point for the radiator hose, so it won't be concourse.

And if you do find out it's the thermostat housing, go with the service manual procedure: forget a gasket and just use straight RTV. A nice 1/8" bead works just fine, and torque down to 30 lb-ft if using factory cast iron intake, or around 20 lb-ft if using aluminum. Obviously make sure both mating surfaces are clean. Permatex makes an RTV formulated for water pumps and thermostat housings that I used that works great.

Straight RTV is the only thing that works for me. Both times I tried gaskets, they leaked - but then again, that may have been because I dressed them with RTV and not an actual gasket dressing. The housing that was on my car when I bought it was some heavily warped, generic O-Ring type... ironically it didn't leak a drop. LOL

[81Blackbird]

Sprinkle some baby powder in the area and wait.  May help if the engine is warm.  You'll see the run in the powder.

[SoupMan]

I had a problem that would only occur while the engine was cooling. To identify the issue I place a towel around the housing and then I tie wrapped a towel around the water bypass at the intake manifold. The intake one was the one leaking. Note that it wasn't leaking during normal operation and appears to stop leaking after the engine was done cooling.

If this is what is happening to you, I would suggest you first try to tighten the bolt that is immediately beside it that bolts into the intake. If that doesn't solve the problem you may need to pull the intake to install a new oring.

[aussieta]

i found the recess in my manifold was not deep enough for the thermostat i was using, which was preventing the housing from fully seating,

[NY81TTASE]

If you're going to change your thermostat, clean both mating sides as good as possible. I think the key to stopping any leak at the housing is to use whatever sealer, assemble, and then let it sit for a day before connecting a hose and adding coolant. Let the sealant cure first.

[Meshuga T/A]

Some thermo housings are alum, the warp.   Check that. 

[10-4onthe79]

Hey Guys,

Thanks for all of the great info. I changed the thermostat housing and gasket. When I did that, I noticed that there was not much coolant below the thermostat. Before I installed everything, I added coolant to fill up the void underneath the thermostat and then sealed everything up. I have not started the engine yet and there is now fresh coolant on top of the water pump. Because of this I now believe it has to be leaking out from where it bolts to the intake. SoupMan, you mentioned to pull the intake and install a new oring. I was thinking I would need to possibly pull the engine as it looks like it is all part of the timing cover and wraps down between the block and the oil pan. If I can fix this without pulling the engine, well, nuff said! Do I have to drain the coolant first for this? The manual doesn't give me much information. Hopefully not to hard of a fix? Any tips or advice is appreciated. I would love to get it taken care of so I can get it out and burn off the tank of gas before it gets too much older.

[NY81TTASE]

If that o ring is leaking, i believe it is easier to remove the intake to replace it. Then  when re-installing the intake after the o ring is installed you leave  all the intake manifold bolts loose, that way when you tighten the long bolt...it draws the intake towards the o ring. Then you tighten the intake bolts.

[10-4onthe79]

OK so I had to laugh at myself. I've been looking for this "o-ring" I need and it never occurred to me that it would be included with the intake gaskets, lol... Just wanted to confirm if anyone can:

Will Fel-Pro MS90205 gaskets fit a 557 block with stock pontiac heads? Performer RPM intake. Any others preferred over the Fel-Pro? Thanks!

[tinpusher]

One thing I do now with my intakes is to separate the water crossover from the intake.
The reasoning for this , if I have a leak it’s isolated from the rest of the intake and I don’t need to remove the entire intake. If I want to change intakes , I don’t need to open the cooling system.
Very easy to do with a cutting wheel or sawsall.

[jugalo]

Any update on this?

[10-4onthe79]

Happy Sunday!  So I removed the intake and got everything super clean. Stock iron Pontiac heads and Performer RPM intake. Got everything torqued down and went out today to add the coolant. LUCKILY, I have a vacuum coolant filler. I tried putting a vacuum on the coolant system and it wouldn't hold. Found a leak on the passenger bottom side of the intake at the front where the coolant would be sitting. Fel-Pro gaskets. I'm going to have to pull the intake again. At least I didn't fill it with coolant yet! I'm going to try the Edelbrock gaskets unless anyone thinks they don't work as well? I figure since they are made for the intake.....

[tinpusher]

Have your heads been milled? If so and they didn’t mill the intake the same amount, your intake will not sit/seal correctly.
Happy Sunday

[10-4onthe79]

Thanks. Yep, Heads were milled, but the intake was done at the same time so I should be good.

[10-4onthe79]

I did some reading last night and it looks like some people recommend to use some sealant around the coolant ports. I did not put anything on the gaskets, because the instructions said specifically not to. They said using sealant could cause them to not seal correctly. Is this something I should have done? I'm assuming I may be able to just reuse the gaskets and add some rtv? I already ordered a set of the Edelbrock gaskets, so either way. Just looking to not do this a third time.    Still appreciative that I didn't find the leak after adding all the coolant though!!

[tinpusher]

Try fitting the intake in position without the gasket to see fit and check for warpage.
If you can get a feeler gauge in there and check to see if you can find something that looks like excessive (Gap).
Since the heads were milled, I’m leaning to something in that direction. Do your intake bolts line up perfectly with the gasket installed? Or they just a little off?
 I always put a little sealant around the water passages, but I also separate the water passages from the intake. Some sealer will not hurt anything.

[10-4onthe79]

Sounds good. I'll give that a shot. The bolts all lined up just fine. The nice thing is the surfaces should still be clean. I also read that you should torque the bolts down about 5 or 6 times. I did NOT do that. I'll check for gaps and if I'm good, then will use a bit of sealant. Supposed to be a little cooler than 90 degrees on Saturday, so that's a bonus too. 

[10-4onthe79]

OK, so over the last several weeks - I pulled the intake and got everything sealed. More coolant appeared and it seemed like the thermostat housing was seeping a tad. Nothing at all where the intake meets the water pump. I pulled the thermostat housing and made sure everything was clean and flat. Re-installed the thermostat housing and all was good. Now, after sitting for a week, there is coolant in the crevice at the top of the water pump, between the water pump and the block. Everything is dry on top. Is this seeping up from the backside of the water pump? Nothing on the floor, it seems to have filled up the void behind the pump and that's it. I am at my wits end right now. I have changed water pumps before, but not a pump with a back plate that is basically the entire front of the engine. Is this possible to even do without pulling the engine? Maybe try snugging up the bolts first? Not sure where to even start....

[nUcLeArEnVoY]

OK, so over the last several weeks - I pulled the intake and got everything sealed. More coolant appeared and it seemed like the thermostat housing was seeping a tad. Nothing at all where the intake meets the water pump. I pulled the thermostat housing and made sure everything was clean and flat. Re-installed the thermostat housing and all was good. Now, after sitting for a week, there is coolant in the crevice at the top of the water pump, between the water pump and the block. Everything is dry on top. Is this seeping up from the backside of the water pump? Nothing on the floor, it seems to have filled up the void behind the pump and that's it. I am at my wits end right now. I have changed water pumps before, but not a pump with a back plate that is basically the entire front of the engine. Is this possible to even do without pulling the engine? Maybe try snugging up the bolts first? Not sure where to even start....

When I reinstalled my stock intake, I did lay down a 1/8" bead of Permatex optimum gray around the coolant openings on both sides of the gasket to help further the seal, and so far no leaks. I mean, look, I get why a lot of people are against using RTV all the time, but the fact of the matter is, these engines are old; and unless you get everything re-milled to remove pitting or warpage, a little bit of insurance in the form of RTV won't hurt anything. You don't need to goop it on like it's butter in Paula Deen's kitchen—just a small 1/16" or 1/8" bead goes a long way. Modern engines are almost gasket-less other than things like intake manifolds and maybe thermostat housings (and even those gaskets are now rubber and pre-molded to fit into impressions on the corresponding part), and their tolerances and machining are FAR superior than what Detroit put out during the time of our cars. You'd think automakers should feel confident using gaskets these days... buuuut they don't. Oil pans, valve covers, and water pumps are usually RTV'd on modern engines.

When you re-installed the intake, did you make sure to FIRST torque the draw bolt with the tab piece in the front that mates the intake to the timing cover, with the o-ring donut seal in between? First thing you do is just finger thread the 10 intake bolts in: don't tighten them down, just thread them in a few turns so they don't fall out. You then torque down that front draw bolt first to pull the intake forward a small amount and make that seal between it and the timing cover. After that is torqued down (official spec is 15 ft/lbs, but I did it by feel and it was fine - don't overdo it, that long draw-bolt snaps easy), THEN you torque down the 10 intake manifold bolts to 40 lb-ft for stock intake, or around 25 lb-ft for your Edelbrock. It also doesn't hurt to apply a bead of RTV at the mating surfaces of where the timing cover meets the intake, it's commonly pitted, at which point you can't fully rely or trust that rubber O-Ring.

As for the thermostat housing, if it leaks again, try it with just straight RTV. That's how the service manual recommends to do it, after all. Every time I tried a gasket, it started leaking.

And then for the water pump, you mean the crevice between the timing cover and the block? I'm assuming this is a Pontiac engine. Coolant in that pit between the timing cover and block is usually because of the previously mentioned o-ring donut seal where the timing cover mates to the intake. A leak coming from the timing cover where it mates to the block would be an oil leak, not a coolant leak; and a coolant leak from where the water pump mates to the timing cover wouldn't end up in that crevice, it would usually find it's way down to the floor. If it were the thermostat housing, usually those leaks will end up in the front flange of the valley pan and travel all the way back to the distributor valley during driving.

I just find it weird you keep springing these leaks. You said you aren't overheating, but are you losing coolant from anywhere else? Like, a lot? Because unless these seal failures are due to repeated installer error, then SOMETHING is over-pressurizing your cooling system. What radiator cap do you have?

[10-4onthe79]

Hey, Thanks a lot for the response. See below for answers:

When I reinstalled my stock intake, I did lay down a 1/8 bead of optimum gray around the coolant openings on both sides of the gasket to help further seal, no leaks. - Did this when installing the intake

When you re-installed the intake, did you make sure to FIRST torque the draw bolt in the front that mates the intake to the timing cover, with the O-ring seal in between? - Yes, did this as well.

You have to torque that draw bolt first to pull the intake forward a small amount and make that seal between it and the timing cover. After that is torqued down (official spec if 15 ft/lbs, but I did it by feel and it was fine - don't overdo it, that bolt snaps easy), THEN you torque down the intake manifold bolts to 40 lb-ft. - Did this as well. Torqued them in sequence several times.

It also doesn't hurt to apply a bead of RTV at the mating surfaces of where the timing cover meets the intake, it's commonly pitted, at which point you can't fully rely or trust that rubber O-Ring. - Did this as well.

As for the thermostat housing, if it leaks again, try it with just straight RTV. That's how the service manual recommends to do it, after all. - Good to know, but I can find no areas that are wet/moist anywhere near the thermostat housing.

And then for the water pump, you mean the crevice between the timing cover and the block? - Yes!

I'm assuming this is a Pontiac engine. - Yeppers

Coolant in that pit between the timing cover and block is usually because of the previously mentioned O-ring seal where the timing cover mates to the intake. A leak coming from the timing cover where it mates to the block would be an oil leak, not a coolant leak, and a coolant leak from where the water pump mates to the timing cover wouldn't end up in that crevice. - Hmm, Interesting. Everything above that area seems dry as a bone. No wet spots or anything and I only see coolant after it sits for several days, maybe a week.

If it were the thermostat housing, usually those leaks will end up in the front flange of the valley pan and travel all the way back to the distributor valley during driving. - Never had that issue.

I just find it weird you keep springing these leaks. - Me too!!!!!!!!!!!!!!!

You said you aren't overheating, but are you losing coolant from anywhere else? Like, a lot? - No, only when it sits for a week or so and once it hits a certain height, it stops. Before when it was leaking from the top, that crevice would fill up and the coolant would spill over onto the garage floor. Now it just sits at that level, which I assume is equilibrium with the coolant level in the block. That's where I got the idea that it was coming up out of the front of the block/timing cover.

Because unless these seal failures are due to repeated installer errors, then SOMETHING is overpressurizing your cooling system. What radiator cap do you have? - O'reilly's special. I don't think that is the case because the hoses don't seem to balloon or anything. Radiator seems to be doing an awesome job as the coolant temp drops dramatically by the time it exits. (I can grab the lower hose going back to the engine.) Annnd the leaks don't happen when running, only when it sits.

Maybe I just need to go grab and LS engine  - I can post some pictures, but not sure how that works since photobucket isn't what it used to be. I could definitely try a new cap, but if it leaks when it sits, would it really help?

[nUcLeArEnVoY]

Hey, Thanks a lot for the response. See below for answers:

When I reinstalled my stock intake, I did lay down a 1/8 bead of optimum gray around the coolant openings on both sides of the gasket to help further seal, no leaks. - Did this when installing the intake

When you re-installed the intake, did you make sure to FIRST torque the draw bolt in the front that mates the intake to the timing cover, with the O-ring seal in between? - Yes, did this as well.

You have to torque that draw bolt first to pull the intake forward a small amount and make that seal between it and the timing cover. After that is torqued down (official spec if 15 ft/lbs, but I did it by feel and it was fine - don't overdo it, that bolt snaps easy), THEN you torque down the intake manifold bolts to 40 lb-ft. - Did this as well. Torqued them in sequence several times.

It also doesn't hurt to apply a bead of RTV at the mating surfaces of where the timing cover meets the intake, it's commonly pitted, at which point you can't fully rely or trust that rubber O-Ring. - Did this as well.

As for the thermostat housing, if it leaks again, try it with just straight RTV. That's how the service manual recommends to do it, after all. - Good to know, but I can find no areas that are wet/moist anywhere near the thermostat housing.

And then for the water pump, you mean the crevice between the timing cover and the block? - Yes!

I'm assuming this is a Pontiac engine. - Yeppers

Coolant in that pit between the timing cover and block is usually because of the previously mentioned O-ring seal where the timing cover mates to the intake. A leak coming from the timing cover where it mates to the block would be an oil leak, not a coolant leak, and a coolant leak from where the water pump mates to the timing cover wouldn't end up in that crevice. - Hmm, Interesting. Everything above that area seems dry as a bone. No wet spots or anything and I only see coolant after it sits for several days, maybe a week.

If it were the thermostat housing, usually those leaks will end up in the front flange of the valley pan and travel all the way back to the distributor valley during driving. - Never had that issue.

I just find it weird you keep springing these leaks. - Me too!!!!!!!!!!!!!!!

You said you aren't overheating, but are you losing coolant from anywhere else? Like, a lot? - No, only when it sits for a week or so and once it hits a certain height, it stops. Before when it was leaking from the top, that crevice would fill up and the coolant would spill over onto the garage floor. Now it just sits at that level, which I assume is equilibrium with the coolant level in the block. That's where I got the idea that it was coming up out of the front of the block/timing cover.

Because unless these seal failures are due to repeated installer errors, then SOMETHING is overpressurizing your cooling system. What radiator cap do you have? - O'reilly's special. I don't think that is the case because the hoses don't seem to balloon or anything. Radiator seems to be doing an awesome job as the coolant temp drops dramatically by the time it exits. (I can grab the lower hose going back to the engine.) Annnd the leaks don't happen when running, only when it sits.

Maybe I just need to go grab and LS engine  - I can post some pictures, but not sure how that works since photobucket isn't what it used to be. I could definitely try a new cap, but if it leaks when it sits, would it really help?

Okay, the intake install clearly isn't your issue, then. Maybe it is the water pump. I guess I can see where a leak from the *top* of the water pump would run back and land in that crevice between the timing cover and block. Honestly, the only time I've ever had coolant in that crevice is because I made a mess and spilled a bunch of it when servicing the thermostat housing. Even when my stat' housing leaked really bad, it never landed in that crevice, it would drip into that depression behind the front flange of the valley pan. Basically like this:


When you did the water pump, did you install the two gaskets dry? Generally, most people use RTV to support the gasket seal for the water pump. Ultra black is a good one for that. It's pretty necessary, since often the divider plate isn't always going to lay 100% flat against the gasket surface of the water pump, so you need the RTV for extra insurance beyond the bolts flattening it out as it's torqued down since it's thin metal. This is especially after beating the divider plate to tighten the clearance.

A radiator cap is a super simple thing to replace to see if it's the problem. I'm guessing you don't have residual pressure in the system after the car cools down, right? Like, once the car is cold after a night of sitting, you can easily squeeze the hoses, and removing the radiator cap doesn't result in a "hiss" of pressure? That may happen for a couple drives after you do a major service on the cooling system that involved lots of trapped air, but it should stop eventually.

Also weird that the leaks only occur when the system is under no pressure... you may have to do some fine-tooth sleuthing to see if you can find trails of coolant. Usually you'll be able to find them. Or pressure test the system again.

Or, think really hard about if you accidentally spilled and made a mess with coolant after servicing the system. Maybe that's all that coolant is in the crevice between the timing cover and block!

[10-4onthe79]

OK so I did more examination. But first more answers:

When you did the water pump, did you install the two gaskets dry? Generally, most people use RTV to support the gasket seal for the water pump. Ultra black is a good one for that. It's pretty necessary, since often the divider plate isn't always going to lay 100% flat against the gasket surface of the water pump, so you need the RTV for extra insurance beyond the bolts flattening it out as it's torqued down since it's thin metal. This is especially after beating the divider plate to tighten the clearance. - The engine builder did this part, so I'm not sure.....

A radiator cap is a super simple thing to replace to see if it's the problem. I'm guessing you don't have residual pressure in the system after the car cools down, right? Like, once the car is cold after a night of sitting, you can easily squeeze the hoses, and removing the radiator cap doesn't result in a "hiss" of pressure? That may happen for a couple drives after you do a major service on the cooling system that involved lots of trapped air, but it should stop eventually. - No hissing. Seems to be good, I do plan on picking up a new cap.

Also weird that the leaks only occur when the system is under no pressure... you may have to do some fine-tooth sleuthing to see if you can find trails of coolant. Usually you'll be able to find them. Or pressure test the system again. - Agree

Or, think really hard about if you accidentally spilled and made a mess with coolant after servicing the system. Maybe that's all that coolant is in the crevice between the timing cover and block! - I actually made an effort to soak all this up because I'm sick of seeing coolant, so I KNOW it was not there.. I wish it was a possibility!! 

So - I drove the car again and there were a couple of drops on the valley pan. I wonder if I didn't use enough silicone on the intake --> water pump? Maybe I have a really small seep? Soooo, I wrapped some really absorbant rope around that part and am going to wait and see. I also looked and I see what you mean about coolant shouldn't be coming up from the cover. Also, this time I have some coolant on the ground by the lower radiator hose. sigh. I usually don't have issues with this stuff because I'm VERY thorough and particular how I do things. the only thing I can think of is maybe I used the rtv too sparingly.  I'll let you know what I find out next. At least the heat index isn't in the 100s anymore now so I can somewhat enjoy working on it. Pics below:

[tajoe]

Lots of wording above, (so I haven't read everything), and I'm just looking at the puddle under the intake/waterpump housing connection, and to me it looks like a classic Pontiac only problem. You mentioned removing your intake multiple times, and (hopefully) using some sorta sealer on the doughnut gasket, but when you torq. down your intake, you "are" (?) tightening the long bolt pulling the intake into the waterpump housing "FIRST", B4 tightening all the other manifold bolts...right? this is the only way to seal that gasket. Not sure if this has already been mentioned.

[Airpowr]

I had multiple leaks I was dealing with, went to NAPA and bought their coolant dye and black light flashlight from Amazon . Made sure everything was dry, brought the temp up to get it all mixed up. And waited till the next day, found all my leaks even the hard ones. Make sure the car is in a dark area.

[10-4onthe79]

Lots of wording above, (so I haven't read everything), and I'm just looking at the puddle under the intake/waterpump housing connection, and to me it looks like a classic Pontiac only problem. You mentioned removing your intake multiple times, and (hopefully) using some sorta sealer on the doughnut gasket, but when you torq. down your intake, you "are" (?) tightening the long bolt pulling the intake into the waterpump housing "FIRST", B4 tightening all the other manifold bolts...right? this is the only way to seal that gasket. Not sure if this has already been mentioned. - Yep. Definitely did this. Not enough torque to break the bolt obviously, but nice and tight before torqueing the intake down multiple times.

I had multiple leaks I was dealing with, went to NAPA and bought their coolant dye and black light flashlight from Amazon . Made sure everything was dry, brought the temp up to get it all mixed up. And waited till the next day, found all my leaks even the hard ones. Make sure the car is in a dark area. - Good to know about this. Might go this route if my absorbent rope doesn't reveal anything. Thanks!

[tajoe]

Lots of wording above, (so I haven't read everything), and I'm just looking at the puddle under the intake/waterpump housing connection, and to me it looks like a classic Pontiac only problem. You mentioned removing your intake multiple times, and (hopefully) using some sorta sealer on the doughnut gasket, but when you torq. down your intake, you "are" (?) tightening the long bolt pulling the intake into the waterpump housing "FIRST", B4 tightening all the other manifold bolts...right? this is the only way to seal that gasket. Not sure if this has already been mentioned. - Yep. Definitely did this. Not enough torque to break the bolt obviously, but nice and tight before torqueing the intake down multiple times.

Well then, if you've used a liberal amount of sealer on that doughnut, torqued it as you mentioned, and the waterpump housing/intake connections aren't "totally" rotted out, then obviously it can't be leaking there. Only other logical explanation is coming from above, either the t-housing (like I think has been covered), or your hose connection, that you also addressed. I would think if it was leaking from above the doughnut gasket, you could see the water/anti-freeze stain dripping down.
 
If not from those, then maybe the water crossover ports in the head, where the frt of the intake gaskets seal, is leaking down into that valley. But if you've had the intake off multiple times, I'm sure you would've taken care of those areas.
 
And lastly, going out on a limb, the timing chain cover/waterpump housing to the block gasket. These aluminum covers are corroding away from age, and if one of the ports from them to the block are leaking, could it be pumping water up into that area? (I seriously doubt it)

[nUcLeArEnVoY]

nd lastly, going out on a limb, the timing chain cover/waterpump housing to the block gasket. These aluminum covers are corroding away from age, and if one of the ports from them to the block are leaking, could it be pumping water up into that area? (I seriously doubt it)

I'm actually dealing with a small leak at the timing cover gasket where it mates to the block. I removed the water pump yesterday in preparation for a new one (old one was a crapola stamped impeller Cardone unit with 0.2" divider plate clearance, no wonder I got warm at idle), and I all of a sudden witnessed a tiny leak start from behind the timing cover on the passenger side and run down the face of the block, near where the heater and lower rsd hoses connect (basically where the coolant opening is on the timing cover to block gasket). I didn't drain the coolant all the way like I should have, and I'm guessing it's because of loosening the big 3/8" long bolts that mate the water pump to the timing cover and then to the block, causing the timing cover to unseat in that area a small enough amount to let water leak. Would make sense given that the intake is literally pushing against the timing cover at the bypass connection where the o-ring is to make that seal, and without the two long bolts to sort of "push" back, this happens. The timing cover gasket has the signature blue color of a felpro so they can't be THAT old, and there was never even the slightest hint of indication of a leak until I loosened those big 3/8" bolts.

I went ahead and drained all the coolant from the block plugs, so she's empty. Gotta let the gasket dry a little bit... I hate paper gaskets. I'm really hoping when I put on the new pump and cinch it all back down to spec, it seals it back up. I haven't started the car yet, obviously, and my oil level hasn't increased, so if the leak does stop after I tighten it all back down, I'm gonna do an oil change just in case. Last thing I want is that leak going into the timing chain area and into my crankcase. If the leak persists after I button it all back up and add coolant, I guess I won't start the car and off the timing cover will go... really don't want to do that, but doing so could prevent future problems.

[tajoe]

I had a rotted housing years ago, and patched it with some kinda 2 part epoxy. Can't remember if it was JB or not, but I remember building it up a couple times over a few days, (weeks(?), and laying it on a sheet of glass, so it would set up flat. Had to do this a number of times, to fill in the low spots. But when it was done, it held for years, till the end.

[nUcLeArEnVoY]

I had a rotted housing years ago, and patched it with some kinda 2 part epoxy. Can't remember if it was JB or not, but I remember building it up a couple times over a few days, (weeks(?), and laying it on a sheet of glass, so it would set up flat. Had to do this a number of times, to fill in the low spots. But when it was done, it held for years, till the end.

Every time I tried a thermostat housing with a flat mating surface and a gasket, I got seepage.. hell, one time, I got a real bad leak. After every try, I'd sand it down again on a piece of glass. I finally bought a NOS thermostat housing with the correct sealing ring cast into the mating surface, and used JUST RTV instead of a gasket. Also block sanded the intake mating surface (stock cast iron) and filled the pits with JB weld. Not a single drop since.

[tajoe]

Can't say I remember any problem leaks, that weren't easily treatable, most the time. I like the Permatex type 2 non hardening sealer. Have had the best luck with that. It's a bitch to clean off, so on valve covers, would only glue the Fel-Pro rubber gasket to the cover itself, and none on the head rail. Could re-use them many times over. Intake gaskets, valley pan gaskets, oil filter housing gaskets, even oil pan gaskets, I could get away with blue RTV.  But on cooling systems, Permatex is for me.