TAC Tech > Mechanical

should my radiator fan run CONSTANTLY?


this may be a stupid question guys, but my radiator fan runs full blast continually when the cars running, it sounds like a b-52 is taking off...i know on modern vehicles, the fan kicks when the vehicle reachs the appropriate, and then turns off accordingly.  im not well versed in fan clutches, but mine appears to be old enough to be the orginal one (btw, i have a stock 79 403) i did some research on here and found out a way to check the clutch is to run the car while its hot, then cut it off and see if it still spins...i cut my car off and the fan stopped with the engine, any thoughts? everything on the car is pretty much OEM (cept for headers) and i do not want to do the electric fan swap as of right now

and i do have another question: my car runs around 200 degrees, which is already higher than i want it to run, well if i figure out a way to make my fan cut off at the appropriate times, then it would run less than it does now...which means the car would run even hotter....im pretty sure im either running a 180 degree therm, or not one at all (its been two years since i last fiddled with that) but i already have a new 180 sitting on the counter that is going into it, as well as a new non a/c water pump, and a new lower rad hose...think itll still run at 200 degrees or even hotter?

The fan clutch should be a "thermal" clutch". It will have a small thermo coil spring visible on the front face, if it is a thermal. The coil makes the clutch engage when heated by the radiator. If there's no coil, it's not a thermal fan clutch, and the fan runs all the time.
If you have a thermal, when the car is cold and first started, the fan will spin, but it's not fully engaged, so spins leisurely. Once the radiator warms up and radiates heat, the clutch becomes engaged and then the fan will speed up and started pulling more air. You can feel and hear this happen if you start the car and watch the engine warm up, and as the radiator heats up, the fan will suddenly become noisier and you can feel air being blown back toward the engine significantly. The fan stopping with a warm engine would be normal, since the fan clutch is engaged, so it would stop fairly quick.
If your thermal fan never engages like that, then you will be running hot.
But, if it's working properly, then there's no problem.
Of course, you must have your fan shroud in place for it all to work right.  

ok, thanks for your help...i didnt know there were two types...ok, i have the thermal...i couldnt get a clean picture of it, but my clutch sits in front of the fan, and on the radiator side of the clutch is a springy coil feeling thing, thats covered in oil, dirt and grime....it prolly safe to assume this is bad (since the egr, pcv were both the originals from the factory and were bad when i got the car)  i already have a new one.

but this brings me to my second point...my car already runs hot at 200, never runs under, never runs over...as i understand it 180 is the optimal temp (i dont run it at high altitudes, or in the winter and it doesnt have a/c) once i get my fan fixed and it doesnt run constantly...wont my temp go up?  i already have a new oem water pump on the way, and i have a new thermo stat and new rad hoses...if these dont turn the temp down ill get new rad....any chance the fan will actually be more effective with the new clutch?  and i have the factory shroud, in new condition already in place

Even though your fan turns now, I have a feeling the clutch isn't engaging, so it's not really pulling as much air as it should. The oil, dirt and grime on the fan clutch could due the fluid from inside the clutch fan leaking out, indicating it needs to be replaced. So, I'd go ahead and put that new fan clutch on and see if it makes a difference.

I noticed the fan clutch on my 79 403 had gone bad a couple weeks ago. It would start overheating just idling. I put on a new fan clutch and it's back to running cool now.

Don't forget that the factory gauge isn't really calibrated...You might try a mechanical gauge just to be sure, but if  yours always stays the same it's probably not overheating


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