I've been chasing an overheating problem forever now. The car is actually not overheating but continually runs hotter than its supposed to. I have a '98 Mistu GST Turbo with 89k. I've replaced pretty much everthing in the coolant system at least once. New radiator, waterpump(w/20k on it now) 2 oem thermostats and oem rad cap, and both temp sensors(gauge and ecu) and confirmed fan comes on once operating temp has been reached. The needle normally runs right in the middle of gauge and now runs 2/3 to 3/4 up gauge. I pulled the first oem thermostat and drilled 2 small holes, which helped and it only ran slightly hotter than normal. Then I purchaced a new 2nd oem thermostat and it runs hot again about 3/4 way up gauge. Also, once it does start running hot I can push in clutch and coast and temp immediatly drops to middle of gauge and then if I put back in gear it jumps right back to where it was. If I leave it out of gear and coast, it will drop down but slowing climb back up to 3/4 of gauge. Please help!
Forgot to mention. First oem thermostat that I mentioned was new as well and had same effect and 2nd oem thermostat, before removing and drilling the 2 small holes. Those this has worked the best I pulled it so I can try to fix the correct way instead of the bandaid fix. I also purchased a coolant pressure tester kit and found the system does hold pressure, although I have not tried this once the car has reached operating temp, not sure if that will make any difference.
February, 21, 2011 AT 2:03 PM
First check that you don't have air in your system. Turn heat on high, run engine from cold to operating temp with rad cap off. (Keep it at idle) Watch for air bubbles.
Also, when traveling at speeds on expressway, will it overheat then? You may want to check for a blown head gasket.
February, 21, 2011 AT 2:14 PM
Also, there's more than one way a head gasket can blow. The first way you've already eliminated by pressure testing the cooling system. That's when the coolant gets into the oil.
The other way is when the engine reaches temp, the metal from the block and head will separate slightly and on the power stroke, the cylinder will push exhaust gas into the cooling system. I've seen situations when a car is still drivable but only under highway speeds. And usually when you shut down the engine coolant will leak back into the cylinder. When you next start the engine you'd see white smoke out the tail pipe for the first few minutes as the engine burns it off.
February, 21, 2011 AT 2:40 PM
I've been meticulous about getting all air out of the system. With the oem (non drilled) thermostat it will overheat during any condition once driven. If I start it and just let sit it will reach opertating temp and maintain. Once drivin, street or highway it goes to 3/4 on gauge. With the drilled thermostat it runs fine on the street(wouldn't even know there was a problem) and on highway it usually ready slightly higher on gauge about, 2/3 sweep.
February, 21, 2011 AT 2:50 PM
Other than checking for belt tightness/slippage and flushing your system for any blockage, you might want to consider checking for a bad ECT or gauge. You could measure the coolant directly and see if it matches what the gauge is reading
February, 21, 2011 AT 3:10 PM
Well the waterpump is run off the timing belt, both of which were replaced about 20k ago. I have a program on my laptop and cable that I can hook up to the obd2 port and will read was temp the ecu can see, because it uses a diff sensor than the one for the gauge or rule that out. Otherwise, if it possibly a headgasket, can/should I do the pressure test after its heated up to possibly reveal a loss of pressure?
February, 21, 2011 AT 4:40 PM
As for the temp sensor, if the sensor is faulty, your scan of the computer will still read that faulty temp. But if the engine temp is different than the gauge reading, then the temp sensor for the gauge or the gauge is faulty.
As for the water pump, it's ran off the drive belt, not the timing belt. Big difference. And do not attempt a pressure test when the engine is hot! U can purchase an exhaust gas leak detector to test for the presence of gas in the coolant.
February, 21, 2011 AT 5:30 PM
Ok, i'll figure out if the gauge is working properly later today. If so, is this a good leak detector to try, or would you recommend something different.
That leak detector is fine. But keep in mind, I'm not saying this is your problem. I'm just giving you other places to look. After all, it's pretty hard to help someone diagnose an issue when I'm not there looking at the car myself. All I can do is give you suggestions according to what you've attempted already.