C2 Fan Clutch Calibration

[Jeff B.]

I read an article today from DeWitts that described the Corvette cooling system in detail. Mostly stuff you would expect, but one interesting factoid was that 60's-70's fan clutches were calibrated for full speed operation at 190 deg, while the later clutches did not reach full speed until 210 degrees. They also indicated that most SR clutches have the hotter calibration. I'm using the service replacement clutch purchased at Corvette Central and it is advertised as the same as the current GM offered SR unit. I do experience an increase in engine temp at a idle up to 195-210 deg. I'm wondering if anyone knows what the calibration on the current GM service replacement clutch is, and if there is a properly calibrated clutch available.

[John H.]

Re: C2 Fan Clutch Calibration

I'm wondering if anyone knows what the calibration on the current GM service replacement clutch is, and if there is a properly calibrated clutch available.

Currently-available GM replacements (the GM #3916141 Eaton coil-type clutch and others) all have the later (higher temperature) emission calibration. They can be re-set to the 60's lower calibration by disengaging the outer end of the bi-metallic coil from the slot in its anchor tab and moving it counter-clockwise 180* to the other anchor tab.

[Jeff B.]

Re: C2 Fan Clutch Calibration

Well thanks John, what an easy fix and I don't have to buy a new clutch. There is nothing like a definitive answer, I guess this will be a short thread! I assumed that this was the case since I never really heard the fan speed up when I expected it should.

[Steve D.]

Re: C2 Fan Clutch Calibration

Is there a technique for restraining the spring while changng tabs? Any words of caution, or is it pretty straight forward?

Steve

[John H.]

Re: C2 Fan Clutch Calibration

Is there a technique for restraining the spring while changng tabs? Any words of caution, or is it pretty straight forward?

Steve

Steve -

Just pull the end of the spring out of the slot in the tab, turn CCW 180*, and insert in the other tab; if the other tab doesn't have a slot, just hook it on the edge of the tab.

[Steve D.]

Re: C2 Fan Clutch Calibration

John

Thanks. One other question/observation: shouldn't the thermostat calibration match the fan calibration?

[John H.]

Re: C2 Fan Clutch Calibration

John

Thanks. One other question/observation: shouldn't the thermostat calibration match the fan calibration?

Sure - midyears used 180* thermostats. Thermostats, by the way, have absolutely nothing to do with controlling higher-than-normal engine operating temperatures (unless they're defective); they only control MINIMUM opeerating temperature, to ensure rapid warmup and adequate heater performance in cold weather.

[Ronald L.]

Re: C2 Fan Clutch Calibration

John, This is a neat trick, is it expected to lower operating temps with an "all new" system?

[John H.]

Re: C2 Fan Clutch Calibration

John, This is a neat trick, is it expected to lower operating temps with an "all new" system?

Ron -

It shouldn't affect operating temperatures at all except at idle or low-speed traffic where the fan provides needed airflow; the fan contributes little or nothing to engine cooling over about 30 mph.

[Ronald L.]

Re: C2 Fan Clutch Calibration

John, I agree with that, did not break 180 last weekend cruising at 40!

Probably can't even prove this affects this A:B now the temperature dropped.

[Michael J.]

Re: C2 Fan Clutch Calibration

Actually, the fan clutch I bought from LIC earlier this year has a special insert in the box describing this adjustment proceedure for the coil on the clutch.