I am in a pickle as I have gone through and replaced everything in my cooling system and still have cooling issues at idle while driving. The car can start up and sit for a long time with no heating issues, but once you start driving it and either sit in stop-and-go traffic or put it in park the temp needle slowly starts moving to the H and will eventually go into the red (always shut off right before that). Any suggestions on what to try next would be greatly appreciated. The
What I have done:
-Replaced to a new 3 row 24” radiator
-New fan shroud
-New fan clutch (for A/C fan)
-New thermostat (tested to ensure it worked before putting it in)
-New Radiator Cap
-New water pump
-Properly set timing
-Bled the cooling system
-Rebuilt 351 W 2bbl
-Head gasket leak test through radiator test that came back negative
Does it ever get hot going down the highway? If not it means you are not getting enough air flow through the radiator. Check to see if there is resistance when you turn the fan when it is hot. Also check your idle speed. Make sure it is about 650 RPM or more. From the factory your car had a thermo vacuum switch to raise idle speed if it started to get warm. Verify that it is still there and working.
There is no overheating when moving down the road. The fan seemed to spin almost at the same rate cool (it is 95degrees out) as it did once it warmed up to operating temperature. When giving the fan a quick flick with my hand at the 12 o’clock position 1 to 2 blades would pass.
Very basic but sometines we overlook… Air pocket in the cooling lines? Did you bleed after filling?
My car used to behave the sane with direct fan which was sitting too deep in the shroud so I removed the spacer to move it half way in shroud, half way ahead toward the engine. That improved it quite a lot.
Coolant mixed 50/50 with water?
Get a point and read thermometer….see what your inlet and outlet temps are. The temp sending units now are all over the place….find an NOS one or even a old one as opposed to a new Standard or Drake Unit. Has the engine been over bored….are the pulleys proper…flow rate can adversely affect cooling….if you feel adventurous … test the voltage limiter on the back of the IP (analog meter only if original)…
I went through the same thing - my thread is the “Hot Cougar” one. What fixed it for me was replacing the original radiator with a 24" ACP aluminum one.
Couple of things I did along the way though:
Flushed the system, including the heater core, and I pulled both block drain plugs. I ran a hose and forced water through the core and didn’t stop until everything came out clean, including the drain plugs.
When refilling the system, make sure to take off the top heater core hose. That will allow air to escape the block.
Run the engine with the radiator cap off. Use a meat thermometer to test the coolant temp and watch when it starts flowing when the thermostat opens.
Check your total timing. I had an over heating problem with my 390.Tried everything possible to cool it down. Long story short the total timing was retarded. Set it to factory specs and it runs cool now. May not solve your problem, but worth a look.
So just to be safe I replaced the thermal vacuum switch as it was original. After driving around that didn’t help at all and the temp continued to climb until it past the first white marker line of the Hot side. It was then that I put it in park and revved the engine to about 1,300-1,400 rpm and the temp needle started to swing back out from the red and back into the safe section. Any other ideas?
Make sure the thermal vacuum switch is plumbed properly.
Center port to distributor. The port that is open when cool goes to the carb ported vacuum port. The other one to manifold vacuum. Unless you have a California car. You definitely need to consult the manual on that one.
Is your advance diaphragm leaking? If so, you will have lousy fuel economy, and the vacuum port switch will make the overheating worse because it will lean out your idle without advancing the spark when it tries to speed up the engine.
Are you running an original carb or an aftermarket carb?
I have an aftermarket carb (Holley 500 cfm street avenger (2 barrel). I did check the vacuum ports and it looked like the distributer and carb vacuum hoses were switched. I switched them back to their proper places (distributer in middle and carb on top). The aftermarket fan shroud I purchased melted today so I will need to wait for a new one to test the cooling. I will also try picking up a new fan clutch as the operation feels the same cool and at operating temp (spins the exact same). I will check with an infrared gun when I put these new parts on in a few days.
