[prexford]

I have a 1971 formula 400. It only overheats when the A/C is on. With A/C off and with a 160, 180 or 195 degree thermostat, car runs at 200. When I turn on A/C is gets up to 250. I have a new fan clucth, fan is on right, car is tuned up correctly. Overheats in summertime and winter.

It started doing it when I replaced my expansion valve and added a accumulator (muffler). I think that my condensor is getting soo hot that it conducts heat onto the radiator. What A/C componet is responsible from keeping the system from overheating?

Thanks for your replies,
Paul

[engineer]

heat removed from AC condenser goes right into the radiator, so inlet air temp to radiator is hotter so radiator is now limited, sounds like a radiator problem to me.

[Region Warrior]

Agree with engineer.
Thats why the factory used 4 row radiators on ac cars.

[prexford]

How can I tell how many rows I have? I took off the radiator cap and I can count 6 rows of tubes (water passges) across the radiator. Do I have a 6 row? If o, prehaps I'm not getting enough air flow through my radiator because it's too thick?

Lastly, can ou recommend a good, OEM looking 4 row radiator to buy?

Thnak you,
Paul

[george kujanski]

Overheats in the winter??????

Not enuf coolant flow or airflow thru the radiator. With all that cold air available there should be no cooling prob. Check water pump, look for blockages in the cooling system including the radiator. Thermostat not opening?

George

[68GeeeTO]

Did you ever get your overheating problem resolved? If so, what was the root cause?

My 68 GTO 400 is exhibiting the same symptoms, with the exception of it over heating when outside temps are 70F or less.

This is what mine does, overheating only when A/C is ON or OFF but, worse with the A/C ON and driving at freeway speeds.
When I get off the freeway, the engine temp comes down to normal.
I have a 160 degree thermostat, I can’t give you the exact temps because I’m going by the factory gauge. I know it runs hotter under the above mention conditions because it starts to spark knock and it will spit up a little coolant at the over flow hose when I shut it OFF. I know the fan clutch, needs replacing but the fan clutch should have no effect when I’m on the freeway because of the airflow at 70+ MPH across the rad and condenser. I’ve watched the coolant flowing through the radiator when the T-state opens, it flows very fast through all the cores and it even looks like it foams up a little because of the fast flowing coolant. The heater core is by-passed, and the radiator is a 4 core that has been re-cored about 5 or 6 years ago.
Any help is appreciated, Thanks in advance
Frank

[engineer]

suggest you start a new post. most don't read posts over several months old.

[pontiac 455ho]

my pontiac does the same thing with ac on it runs 195 with 180 thmostant highflow from milodon thenit goes to 240 turn it off and temp goes to normal ac is new and motor in new hope this helps
ps use royal puple ice for cooling syestem and royal purple motor oil thise will lower your temp a few degrees

[prexford]

I found that my problem was a stuck lifter that wore down the cam shaft lobe, thus burned oil and over heasted the motor. this might be extreme to what your situation is...I don't know. I also found that the car was hard to start because of the force on the camshaft with the stuck lifter. May try changing your thermostat to a 180 or 190, my 1971 400, the manual says a 190 themostat. if you have a 160, it will open sooner, thus not letting the water cool long enough inside the radiator. i tried a 160 when i was having the cam problem and moved to a 180 and cooling actually improved.

good luck

[68GeeeTO]

Paul,
Thank you for answering, as your problem was a camshaft, my cam is new and new lifters and rockers.

I am going to repost as engineer suggested

Pontiac 455ho, let see if we both can't get our overheating problem resovled, I will start a new thread.

Thanks to both, and prexford, I'm glad your problem is resovled, take care
Frank

[prexford]

The problem was the radiator. The over heating got worse with a/c on. this lead to car always running hot, which lead to the lifter getting stuck and the cam wearing out. I did'nt want to think it was my radiator, but it was. Installed a factory looking aluminum radiator and running cool.