Fan clutch and fan questions


New member
Another rookie issue with my engine temp too high.
63 Tempest w a 65 Le Mans 327, 389 headers. Heating up at low speeds, and traffic. It's got a flex fan in it, no fan clutch. I drained and re filled the radiator, nothing too nasty in the radiator. Swapped out the 180 degree tstat for a 160 degree, then filled with 50/50. Still running hot. Wondering if I have the wrong fan? I don't race her, just weekend cruiser. Got good water circulation in radiator. After market aluminum radiator, is there a way to see if it's a 3 row or 4 row? Ill fitting aftermarket shroud, adding to the fun. Had the timing adjusted recently. Trying to start with the easy stuff. Thanks


Staff member
You need a thermal fan clutch and fixed blade fan and shroud.
What did you set the timing to?
If you have a vacuum advance distributor make sure the vacuum line has suction at idle and above idle.


New member
Had a carb shop here set timing, adjust carb. Vacuum had suction.
Had an idea that the flex fan was an issue. Seems like it's for racing. I'll try to find a thermal clutch fan. Appreciate the help, again.


Active member
Belleville MI
If changing to a clutch fan does not cure the issue, I suspect a water pump to backing plate issue. The Stock Pontiac water pumps used a cast impeller like below (note the pictures are from later 69-79 Pontiac water pumps but the same applies to the earlier pumps)
Most rebuilt Pontiac water pumps I have seen (usually bought at the local auto parts store) use a generic stamped impeller like below.

The stamped impeller design has 2 issues in a Pontiac V8
1- It does not move enough volume of coolant at lower RPM's
2 - It does not fill the gap well to the rear backing plate well. This also causes a lose of Volume, and allows the coolant to cavitate around the stamped impeller.

There can also be issues with the backing plate be corroded or pitted, not being fit well to the water pump impeller, and there is a seal that goes bad with age on a coolant transfer tube coming into the back from the engine block. (the later designs have 2 of those transfer tubes but you 1965 block should only have 1.) Below is a link to a site that explains it better than I can.