Running HOT!

I have 2001 Pontiac Aztek V6, 200k miles. I had a intake manifold gasket leak, before i could get it fixed the heads blew. I replaced the heads(new), radiator, water pump, thermastat, and a few hoses. Car is still over heating. If I drive the car in the neiborhood and its fine, but its when I put it on the highway she gets hot. I took this car to 4 machanics, and no one can figure it out. Does anyone have any insite on why this may be happeneng. Thank you in advance for your responses.


When you say running hot can you provide more detail. Is is overheating? Are you judging this solely from the dash gage reading. If you can get your hands on an optical pyromenter and see what the upper radiator hose is when it appears hot and at normal dash gage readings. More and more techs use them. My plummer even used one when he replaced and set up a new water heater.

Make sure you have a 50/50 mix of antifreeze to distilled water in the radiator. This will give you better heat transfer.
Post back when you have more info.

Also make sure that the cooling system has been completely burped - no air. If you have bleeders, use them through several heat up cycles. You can also loosen the upper hose clamp, stick in a screwdriver to bleed. To the good suggestion of checking actual coolant temp, you might also want to check the temp sensor.

There is a bleeder right next to the water pump on this engine that needs to be used any time coolant is added to the radiator. Unfortunately, you also need a tool that is called a “spill free funnel.” They sell them on the tool trucks (snap-on, matco, mac) for about $20 or so. It’s a big funnel with adapters to fit on different radiators, and a 45 degree elbow for angled GM’s like your Aztek. Put on the spill free funnel, open the bleeder, and pour the coolant into the funnel. This is the only effective way to get all the air out of this engine.

I have a similar problem with a 2000 Alero V6, I replaced the intake manifold gasket, thermostat, hoses and still have overheating. Do your electric radiator fans run on high speed when your AC is on? If not they may be unplugged or a temperature sensor or relay for the fans may be defective. When the car is at operating temp at idle the cooling fans on the radiator should be running on low and them kick up to high speed (high speed to me is defined as NOISY) if you figure out what is causing it let me know I still have not found the culprit in mine.

Overheating, what’s strang about this is it wont overheat if the car is running and in park, but it will once you drive on a long stretch of road(highway). I replaced everything I could think of(fan relays, temperature sensors). And yes I did take it to a specialist to run diagnostics on the car. He couldn’t find a problem, but while he was doing this the car was in park. The fans kicked on and off when they were suppose to, hi and low. I’m all out of ideas.

The engine oil helps to cool the engine. Is the engine oil level on the mark?
Automatic transmission fluid is cooled by the radiator. Is the A/T fluid level on the mark?
The air conditioning coolant is cooled by a “radiator” in front of the engine coolant/ A/T radiator. Is the AC off, or on, when the engine is “running hot”?
Besides the dash gauge, have you measured the temperature across the radiator?