[Charlie Brengun]

So my car overheats when I let it idle. I know I need to address my distributor as it has no vacuum advance (old mallory unit).

With my previous electric fan setup the car would be OK, I changed it back to a used clutch fan setup and am wondering if the clutch is worn out.

How easy should it be to spin the fan when the engine is warm?
This video is what it does with the thermostat housing at about 180 degrees.

https://youtu.be/r3c09rKe4LE

Could this be the fan clutch that is done for?

[Trevor78]

Idling shouldn't be when it overheats, I'd be looking into why. If the temperature is getting up then the clutch should be getting fairly firm. Luckily they are cheap and easy to swap.

[i82much]

maybe lower the lockup temp.

http://midamericachevelles.com/tech/...tch_adjust.pdf

[Schurkey]

Lots of fan clutches get blamed when the radiator is shot.

A failed radiator can't transfer heat to the air. Therefore the fan clutch never gets hot enough to engage.

Fix the vacuum advance before screwing with anything else.

[geeteeohguy]

Originally Posted by Schurkey

Lots of fan clutches get blamed when the radiator is shot.

A failed radiator can't transfer heat to the air. Therefore the fan clutch never gets hot enough to engage.

Fix the vacuum advance before screwing with anything else.

This^^^. Fix the known issue first (no vac advance) and go from there. Overheat at idle is not enough air through the core. If it doesn't run hot at high speed, likely a fan issue.

[Formulas]

the clutch fan knows nothing about core eng temp it only knows what air temp is coming from the radiator passing over the clutch in a running state..
the clutch always turns the fan but at certain temps the clutch engages more solidly increasing fan speed to keep temps in a range

so sitting still like in your vid it should have minimal engagement

however at minimal engagement the fan should not rotate much after you let it go by hand

i would say yours could be marginal by how much it continues after a hand push

and if you replace it i would use the middle clutch the heavy duty one never seems to let up on its grip and the light duty one is made for cars without a/c i believe

the way to tell them apart is light duty just has fins on the front med has the exposed thermal coil in the center with more fin area and the heavy / severe duty ones have the exposed coil and about double the fin area as the medium units

since cooling was fine with an electric and you changed to a old clutch fan and now it overheats that would point to a recent change as the culprit

[Schurkey]

It is possible--but really unusual--for a car or light truck--to need a "Heavy Duty" fan clutch. The standard-duty clutch is all that's required with most automotive fans.

Even if the "Heavy Duty" clutch will physically fit, most fans aren't aggressive enough to force the clutch to release. They "cool better" because they DON'T release, therefore fuel economy suffers, they take excess power, they add to the load on the belt, and they make excessive noise. On higher-RPM engines, they can cause the fan to explode due to over-speed.

https://www.haydenauto.com/en/techni...q-fan-clutches (my emphasis)

Each fan clutch type is designed to simulate the performance of the original equipment clutch that it replaces. All fan clutches are for specific applications and should be applied only on the vehicle for which they are cataloged. Use of the incorrect fan clutch may result in poor cooling, excessive noise, reduced fuel economy or fan clutch failure.

• Standard Duty Thermal: Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch (1-1/2" of pitch). Flat plate impeller design with 30 sq. in. of working surface.

• Heavy-Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans (2 1/2" of pitch). Land and groove design with 47 sq. in. of working area allows higher operating RPM's.

• Severe Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 sq. in. of working area. Larger working surface provides cooler running and longer life expectancy.

[Charlie Brengun]

I'm sure this wasn't helping either, I was expecting a stuck thermostat not a restrictor. Anyway I had a 195F thermostat lying around. I have the day off Tuesday so that will be a good moment to see how it does with a thermostat in place.

[67drake]

Originally Posted by Charlie Brengun

I'm sure this wasn't helping either, I was expecting a stuck thermostat not a restrictor. Anyway I had a 195F thermostat lying around. I have the day off Tuesday so that will be a good moment to see how it does with a thermostat in place.

Don’t you love find mysteries on a “new to you” car?
I’m just starting to debug a car of my own that I feel the previous owner had no knowledge of car basics or common sense.