Fan Clutch question..
 

I have a 1970 base 350. How do I check to see if the fan clutch is working properly? The fan seems to turn the same at start as it does when warmed up.

I did some research on my fan clutch. According to the part number, it seems that when I used some old parts during rebuild, the clutch that I used came off of a 1984 305. This might be a stupid question, but is this clutch useable on my car? I don’t have a lot of education on fan clutches. It seems to operate properly but I still have a slight heating issue.

There are several threads on the forum that discuss fan operation. One trick is to count the revolutions of the fan immedately after shutting the engine down - don't remember the count, but it is discussed in the threads. Good luck.

The clutch fans cover a variety of engines , some engage earlier than others by their thermostatic spring which faces the radiator. Even if the clutch is not specif to your car doesn't mean a new one will fix your heating issue.
What's your car doing ?

It will heat up to about 215 on the hwy at about 60mph, and stay there. When I slow down to a sustained 45 or 50 the temp stays high and will not decrease. In town the temp seems to stay around 195. Not sure what the problem is, 215 is not that bad and probably not hurt anything, but it just doesn’t seem right.

Drill 2-3 3/16 holes in the apron of your thermostat....and make sure it's rated at 180f.....

bet the problem is solved....

mrvette, I'm just curiuos, what does drilling the apron do? Allow better flow?

I thought that the stock thermostat was a 190*.

A fan clutch should spin free several times after you turn the engine off. It is designed to pull air through the radiator at slower speeds, especially at idle. It should slow down, relative to the engine rpms at higher speeds, factory installed (thermal) fan clutches have thermosats attached to the front.It should engage the fan at higher temps, even at higher rpms. Make sure your thermostat is good, it's probably best to either removed it and test it in a pot of water on the stove with a thermomoter, or better yet, replace it with a GOOD quality (stant or GM ) T-stat. Another important factor is to determine if the cooling system is working correctly. The waterpump impeller may be rotted out or loose, the radiator may be plugged or partially plugged. On radiators working properly, I usually see a temp drop of approx 30 degrees F using an infrared (Raytec) temp gun between the inlet and outlet. If the coolant travels through the radiator too fast or too slow, the raditor won't have be able to transfer the heat from the coolant to the air flowing through the fins.You also want to inspect the front of the radiaot carefully and look for dirt, vegitation, hair (dog,cat,etc) perventing air flow through the fins. Most importantly, use a infra-red temp gun on the thermostat housing, and make sure your 215f readeings are correct. Harbor freight sells inexpensive infra red temp guns, you may also want to experiment and see iinporanehow much the coolant cools while it is in the upper radiator hose, you'll usually see a 10-20f degree drop in the radiator hose, then drop another 30f across the raditor.

Three more points, make sure your water pump pulley is correct and the pump is turning the correct rpm, make sure your fan is turning the correct direction, if it's installed backwards, you'll be pushing hot air back through the radiator, last, while I beleive a 79 turns the corerct direction, serpentine belts systems usually turn the water pump backwards, if the waterpump or fan clutch is designed to turn backwards, well it'll never work correctly.

You have some good points but I have to correct you on this one. A fan put on backwards won't push the air in the opposite direction , it will just be less efficient .

I believe the idea is to allow any trapped air to escape past the therm.

Here is what I'd do and have done on my 79, in the following order:

1) ensure belts are tight
2) check hoses. Squeezing them should be firm not squessy
3) replace therm with a 180*
4) replace water pump
5) replace fan clutch

When my fan clutch failed, the check I did was to start the engine cold and immediately stop the engine and count the number of fan revs. Compare this number to fan revs after stopping the engine after it has warmed up to op temps. The revs on a warm engine should be significantly less.

1984 engines had 195F thermostats and fan clutches to match. If you want to run a 195F stat in your car, then you should expect operating temps over 200F except in winter.

If you want your engine to run cooler (ie, 180F), you will need to change the thermostat and the fan clutch. With a 180F stat in your car, your present fan/clutch will not turn on unless the engine begins to overheat. And, once the fan does come on, the engine will still stay in the 200's.

Also [for clarification], with the fan NOT engaged (running cold), the blades should spin freely for several revolutions when you turn the engine OFF. If the fan has reached the temperature for it to engage, then it will only turn once or twice when you shut the engine OFF. If the fan is HOT and it just spins when you shut the engine down, the clutch is no longer functional.

In general, this is a good post, but Roger pointed out one flaw, and there is another contained in the part I quoted. In engineering school, they taught me that the amount of heat transferred from a radiator is dependent on the temperature difference between the air and the radiator, and the speed of the flow of air over the radiator. The speed at which the coolant travels through the radiator has nothing to do with how much heat is transferred, at least not directly. In other heated debates on radiators, people have come up with all kinds of whacky situations to try to prove this wrong, but I have grown tired or performance comparisons to Argon atmospheres on Jupiter and the like.

:iagree:
I've read that if the fan continues to spin after shut down, the clutch is shot.
:thumbs:

:rofl: That was a good one.

I seem to remember someone writing in an earlier thread (a year or so ago).
Get the car up to temp, say on the highway, then sit in traffic. If the temp cont. to rise the clutch is bad. (my 79 was doing this very thing)

I went through my entire system recently. My fan was damaged from bubba not installing the shroud correctly, which I felt torched the clutch as well.
My rad is new so left that alone. Drained and flushed the fluid ( cheap job, 4.99 for the Prestone flush kit, prestone flush fluid and $20 or so for new fluid). You can do it in your driveway. Orig. fluid was brown and rusty. It took 10 gallons to get it clear and that was after it was drained.

Replaced the T-stat (180*) and gasket. Cleaned the housing as well. That was nasty too.

Next was the fan. I know they're not always loved here, but I put on a flex fan for $40. I have full intent on putting in an electric that my Dad handed me the day after I did all this.

Since then she's never gone over 190. My engine bay seems cooler as well. The HP increase didn't hurt either.

Food for thought!

I just had a cooling problem with my 76. It would get up to 260 and wouldn't come down. I took off the flex fan (that came on the car) and put the clutch from my 73 and a spare fan on. It then stayed around 210 even though the clutch was bad. I then bought two new clutches (one for 76 and one for 73), and replaced them. I got the heavy duty ones from Advance Auto. Now the temps on the 76 stay right around 180.

To the OP, do you still have your spoiler on the front of the car? For the temps to be going up while on the highway and down while in town, it sounds like there isn't enough air going across the radiator when at speed. If the spoiler is messed up, that will limit the air going to the radiator. The fan is probably pulling enought air around town to keep it cool.

The spoiler is still there and in good condition. The car had the A/C removed by a previous owner and I just reinstalled a new parallel A/C condenser. It's installed in the exact position as the original condenser. Would this account for the temp increase?