test fan clutch?

[don whitehead]

Anyone have any ideas on the best way to test a fan clutch to see if it is engaging properly. What is the temp at which it should engage,its a 283 270 mtr with 500 miles on rebuild. Has a 5 blade fan. The car heats up gradually, up to 210 only at idle!!, but everything else checks out. The temp is accurate. It runs ok over 2000 rpms. Thermostat is ok a 160 hi-po, new alum dewitts radiator, 50-50 mix, I have replaced the fan clutch once, maybe the replacements do not work properly? New waterpump too. Timing is right on, right plugs, dwell set right, engine all at spec.
Baffled!

[Duke W.]

Re: test fan clutch?

The fan clutch is controlled by the temperature of the air exiting the radiator. When the engine is cold the fan should turn quite freely. Check this and then again when the engine is hot after a lot of idling. Shut it down and immediately turn the fan. There should be a lot more resistance.

You should also verify the temp gage with an IR gun, a meat thermometer, or some other cross check. Could be your sending unit is not the correct calibration. This seems to be a common problem.

I would recommend that you use a 180 degree thermostat. Remember, the thermostat establishes the LOWEST operating temperature of the engine and is not a cure for overheating.

A 270 may tend to run a bit hot at low speeds in warm weather because it doesn't have vacuum advance.

Duke

[Duke W.]

Re: test fan clutch?

The fan clutch is controlled by the temperature of the air exiting the radiator. When the engine is cold the fan should turn quite freely. Check this and then again when the engine is hot after a lot of idling. Shut it down and immediately turn the fan. There should be a lot more resistance.

You should also verify the temp gage with an IR gun, a meat thermometer, or some other cross check. Could be your sending unit is not the correct calibration. This seems to be a common problem.

I would recommend that you use a 180 degree thermostat. Remember, the thermostat establishes the LOWEST operating temperature of the engine and is not a cure for overheating.

A 270 may tend to run a bit hot at low speeds in warm weather because it doesn't have vacuum advance.

Duke

[Joe L.]

Re: test fan clutch?

Don------

I've always found it difficult or impossible to test these fan clutches, especially if you're just trying to test the "engagement" temperature and the unit is in otherwise good repair. Completely failed and worn out clutches are pretty easy to determine.

A few considerations:

1) If you are using the current GM SERVICE replacement fan clutch for your application, GM #3916141, current examples of that fan clutch do "engage" at a somewhat higher temperature than original clutches;

2) If you are using an aftermarket-sourced fan clutch, especially a non-thermal variety, the type of situation that you're experiencing is quite common;

3) 210 degrees at idle is not really all that bad, as long as it doesn't get too much hotter than this.

[Joe L.]

Re: test fan clutch?

Don------

I've always found it difficult or impossible to test these fan clutches, especially if you're just trying to test the "engagement" temperature and the unit is in otherwise good repair. Completely failed and worn out clutches are pretty easy to determine.

A few considerations:

1) If you are using the current GM SERVICE replacement fan clutch for your application, GM #3916141, current examples of that fan clutch do "engage" at a somewhat higher temperature than original clutches;

2) If you are using an aftermarket-sourced fan clutch, especially a non-thermal variety, the type of situation that you're experiencing is quite common;

3) 210 degrees at idle is not really all that bad, as long as it doesn't get too much hotter than this.

[don whitehead]

Re: test fan clutch?

Thanks Duke,
I verified the temp guage , its fairly accurate. Will try and see if I can detect any change in resistance. Youu feel a 180 therm is in order? I realize that it controls the operating temp, you think 180 is better? The 160 has the larger opening which was recommended for that motor? Iam hoping that the temp will drop after the engine breaks in some more too. I have yet to run it on a 90 degree day, as its still cool in NJ. I worry that it might get higher.

[don whitehead]

Re: test fan clutch?

Thanks Duke,
I verified the temp guage , its fairly accurate. Will try and see if I can detect any change in resistance. Youu feel a 180 therm is in order? I realize that it controls the operating temp, you think 180 is better? The 160 has the larger opening which was recommended for that motor? Iam hoping that the temp will drop after the engine breaks in some more too. I have yet to run it on a 90 degree day, as its still cool in NJ. I worry that it might get higher.

[don whitehead]

Re: test fan clutch?

Duke, Someone also suggested using a 6 in fan pulley rather than a 7, any thoughts?

[don whitehead]

Re: test fan clutch?

Duke, Someone also suggested using a 6 in fan pulley rather than a 7, any thoughts?

[Duke W.]

Re: test fan clutch?

Again, the thermostat establishes the MINUMUM operating temperature. I don't know who recommended a 160, but the original as designed by GM was a 180. That's the recommendation I follow.

The 180 was choosen to reduce condensation in the crankcase, and it was compatible with ethylen glycol antifreeze. The OEMs used to use 160 thermostats with the old alcohol based anti-freezes as they tended to evaoporate with time.

Other 270 owners should be able to give you anecdotal evidence of operating temperatures. As I said, lack of vacuum advance will tend to make an engine run hotter at idle and low speeds, but I doubt if a 270 should operate that hot in your cool spring temperatures. There may be some other issue, and the first to consider is radiator cooling performance.

Radiators suffer from deposit buildup over time and it's tough to test. Water may flow through it freely, but the deposits significantly reduce heat tranfer performance. If you have an aluminum radiator, there's no way to repair it - replacement is the only option. If it's brass, the end tanks can be removed for inspection and the tubes can be rodded out.

What type of radiator do you have and what is it's history - age, repair/service history, etc.

Duke

[Duke W.]

Re: test fan clutch?

Again, the thermostat establishes the MINUMUM operating temperature. I don't know who recommended a 160, but the original as designed by GM was a 180. That's the recommendation I follow.

The 180 was choosen to reduce condensation in the crankcase, and it was compatible with ethylen glycol antifreeze. The OEMs used to use 160 thermostats with the old alcohol based anti-freezes as they tended to evaoporate with time.

Other 270 owners should be able to give you anecdotal evidence of operating temperatures. As I said, lack of vacuum advance will tend to make an engine run hotter at idle and low speeds, but I doubt if a 270 should operate that hot in your cool spring temperatures. There may be some other issue, and the first to consider is radiator cooling performance.

Radiators suffer from deposit buildup over time and it's tough to test. Water may flow through it freely, but the deposits significantly reduce heat tranfer performance. If you have an aluminum radiator, there's no way to repair it - replacement is the only option. If it's brass, the end tanks can be removed for inspection and the tubes can be rodded out.

What type of radiator do you have and what is it's history - age, repair/service history, etc.

Duke

[Duke W.]

Re: test fan clutch?

This is what I call "amateur re-engineering of the system" to solve a performance problem. When new I'm sure the system provided adequate perforance and some margin for degradation.

We've been through these discussions before. Guys put in low temp thermostats, "high flow water pumps", big fans, etc. but the problem usually persists. The last step is to replace the aluminum or rebuild the brass radiator. In every case that was discussed, I recall that this solved the problem. A new aluminum radiator is expensive, but all the other money spent just went down the drain.

Duke

[Duke W.]

Re: test fan clutch?

This is what I call "amateur re-engineering of the system" to solve a performance problem. When new I'm sure the system provided adequate perforance and some margin for degradation.

We've been through these discussions before. Guys put in low temp thermostats, "high flow water pumps", big fans, etc. but the problem usually persists. The last step is to replace the aluminum or rebuild the brass radiator. In every case that was discussed, I recall that this solved the problem. A new aluminum radiator is expensive, but all the other money spent just went down the drain.

Duke

[don whitehead]

Re: test fan clutch?

Hi Duke,
Thx for the response. Its a brand new Dewitts top=tank alum hi flow rad. This is what is puzzling me. When the car is moving, its nailed at 160 degrees. Brand new waterpump, belt tight, new engine block, manifold, pistons, rings, valves, balanced, I spared nothing! Gauge is accurate. Tuned on a Sun machine even. Put in synthetic oil after break in too.

[don whitehead]

Re: test fan clutch?

Hi Duke,
Thx for the response. Its a brand new Dewitts top=tank alum hi flow rad. This is what is puzzling me. When the car is moving, its nailed at 160 degrees. Brand new waterpump, belt tight, new engine block, manifold, pistons, rings, valves, balanced, I spared nothing! Gauge is accurate. Tuned on a Sun machine even. Put in synthetic oil after break in too.