New guy here with a strange problem, I have an 1976 pontiac 455/400. My problem is when I am driving at any speed the car wants to overheat, if I stop it cools down, this seems backwards to me and I have never seen anything like this. I have change the thermostat stat, and plan on changing the distributor because now it has an Untilizied system. Thanks for any ideas!

 

Is your fan installed backwards? When was the last time your radiator had been serviced?

 

Lower hose collapsing? How is timing and mixture?

 

Thanks for the replies, I will change the lower hose too see if that helps. I have a new distributor in route to me, after I install it I will update.

 

The lower hose could also need a spring inside it to keep it from collapsing under the vacuum caused by the waterpump. Just another thought.

Adam

 

Need to check the fan clutch also if it is not operating properly will cause a overheating problem.

 

If it is a hose collapsing you should be able to simulate that by running the car at a fast idle. This would provide the opportunity to do a visual on the lower hose also to see if it sucks in.

If it doesn't overheat at fast idle it could be the fan blowing backwards (as oldcutlass stated). If this were a multiple choice question on a test I would choose fan on backwards....

Another thing that made a monkey out of me when I was a young mechanic in the 1970's working for my brother was a fan belt that didn't set properly in the pulleys. This particular incident was a 1965 Mustang that would charge at idle but not at higher engine speeds. After farting around with the customers car for a while my older brother told me to shut off the engine and he easily rotated the pulley on the alternator. It turns out that the fan belt was too big or too small to fit in the pulley correctly and at higher speeds it would slip and the car wouldn't charge. The belt was tight and did not make noise at all. I installed a new fan belt, tried to turn the alternator pulley to see if it slipped (which it didn't), started the car and it charged fine. If this is the case with your car overheating you should be able to get the fan to slip (by hand with the engine off) easily. This is a long shot but very easy to check.

 

i had a vw do something similar at the body shop i worked at. we could idle the car al day long and maybe trip around the block and it was fine, but as soon as you actually drove it, it would quickly overheat,street or highway. system was full and bled properly. turns out the pump impeller on those cars are plastic and are prone to breakage. a new pump set it right. obviously, your impeller would be steel or cast but if the fan is rotating in the right direction, your system not airbound for any reason and the t stat checks out , i would check the pump for a possible loose impeller as last resort.

 

My experience with 455 Pontiacs is that they tend to run warm- I always felt like the 428 was as far as they should have taken that engine, but when Buick and Olds had 455s and Chevy a 454, couldn't very well get left at the gate, could they?

Pontiacs use a metal sheet between the water pump impeller and the back area of the timing cover. I've seen those get holes and cause overheating mayhem.

 

Thanks for all the help I changed the distributor,themo-stat,lower hose. She is holding at 220 no higher.
Now she has a carbs problem new carb maybe two years old,when idling wants to flood its a quadra jet. I have changed the fuel filter, still flooding!

 

installing the fan backwards will not change the direction of air flow,but it will change the efficiency of the fan,to change the direction of flow you would have to change the rotation of the fan.

 

generally speaking if your car runs hot stopped its air flow and if it runs hot driven its coolant flow.i had a car in my shop(olds powered) you could let it idle for hours but within 2 miles driving the temp skyrocketed.the radiator was plugged.maybe its plugged or the hose is collapsing.