QuestionThe vehicle is overheating. The heat gauge fluctuates constantly from HALF WAY to just before RED. As the car
gets hotter the heater turns to blowing cold air. It then
starts to cool and the hot air comes from heater.
I replaced the thermostat (TWICE). Flushed the system TWICE
Pressure checked and checked for AIR Bubbles. Took the hoses off to make sure there was no blockage. A mechanic
checked the temp. on both sides of the rad and the rad itself and said that was fine. He checked for a head gasket
leak using the solution that changes colour if combustion gases are present and no leak was indicated. ANY IDEAS??
AnswerHi Eric,
From what you describe it sure sounds like the engine has a cracked head or head gasket problem. When that happens the temp. gauge will go to the hot range but cold air comes out the vents. And it will fluctuate rather quickly...It could go cold-hot-cold in a matter of 5 minuets. Also antifreeze will go past the radiator cap and fill up the overflow bottle even to the point of spilling onto the ground. That said there might still be a different cause so lets recap some scenarios some of which you have already done.
The coolant concentration needs to be between -34 and -60 degrees F. If out of this range then it can cause overheating. And the system needs to be full with all air out of the system. If this problem happened after getting the coolant flushed then maybe the 3 seal tablets weren't put in which helps seal small leaks before they become problems. DO NOT USE barsleak or anything else to pour in because it might not seal properly. The tablets can be gotten at any GM dealer.
The radiator cap must be able to hold pressure. For every 1psi the cap can hold it raises the boiling point aprox. 4 degrees. So if water boils at 212 degrees F then having a good 15psi cap on would raise it 60 degrees to 272 degrees which ordinary engine should never run. Also there can't be any leaks anywhere else in the system or the boiling point will be lower.
The waterpump needs to be able to circulate the anti-freeze. Waterpump impellers have been known to rust to the point of looking like a saw blade instead of a fan blade if cooling system flushes haven't been done. Or the blade could spin on the shaft and waterpump belts break.
The antifreeze has to be cooled by the radiator. It the tubes inside the radiator are restricted due to lack of flushes then the engine can't cool. Also if cardboard, leaves or other debris is found infront of, between or behind the rad./condenser then it can't cool either. Make sure both cooling fans turn on at hi speed.
The temperature gauge needs to be checked for accuracy. The best way is with an infra red thermometer and testing near the temp. sensor for the gauge as well as other points on the engine and red. Maybe there is a hot spot and it can be traced to a blockage/restriction.
And that brings us back to cracked heads or bad head gaskets which is what I feel you have. If the engine just started to overheat it might be tricky to catch a combustion leak the first time out. You might need to run the engine for 30 minuets so it gets good and warm before the exhaust gasses get into the cooling system. I might suggest that you purchase that test kit from Napa or other bigger auto parts store and run your own test for up to 1 hour of continuous running and see if you can get the color to change.
The Northstar engine has problems with the threads pulling out of the block for the head bolts so alittle more testing should hopefully turn up the cause of your overheating. Hope this helps, Bill
