I have a 1997 Sunfire GT, 2.4L, 223k miles, that overheats at idle. When the AC is on the radiator fan works normally. When the AC is off the fan does not turn on. Historically the temperature is in the middle of the temperature gage. If I don't turn on the AC, the temperature spikes to the yellow area.
I've read the Haynes manual and all of the radiator fan related posts but haven't found an answer to this problem. The fan works when hooked directly to the battery. The relay checked ok. I've replaced the ECT (engine coolant thermistor) because I didn't know how to test it and it was only $12. The water pump and thermostat are 9 months old but don't seem to an issue (upper radiator hose is firm).
If I unplug the connector to the ECT, the radiator fan will come on, but I loose the temperauture gage (obviously). This following link seems to share most of my symptoms, but doesn't say what the fix was. The problem seems to be that the fan is not commanded to turn on by the PCM or because of a continuity problem.
http://www.j-body.org/forums/read.php?f=11&i=124941&t=124941
Some more background if it helps. Fan motor was replaced 2 years ago. First overheating incident occured a month ago and I found the connectors to the fan were loose and the connection was intermittant. Since it has been hot out, the air conditioner has been on all the time and I didn't notice a problem until the outside air temperature has cooled. The radiator fluid was replaced when the water pump was fixed along with the reservoir cap. It's still a good little car and I would like to keep it a little longer.
Any help would be awesome.
check the cooling fan relay?????
JBO since July 30, 2001
My 98 cavy did this exact thing. Word for word, Except I would magically lose a little water every month or so. Turned out to be blown head gasket. Fan worked normal after I repaired the failure.
Your WHAT hurts?
Thanks for the response. I managed to get a friend to come over with his computer and was able to confirm that all of the electrical components were working and were being commanded by the PCM. The fan finally came on at 225 F and shut off at 224 F. My buddy convinced me to replace the thermistat even though it had just be replaced within the year. I bought an OEM thermistat and my problem seems to be fixed after a couple days of test driving. Just to satisfy my curiosity, I took the old thermistat, put it in some boiling water and it only opened about 3/16". I guess there was enough flow through the radiator with the AC on to keep the engine temperature at normal, but not enough to cool it with the car at idle until the temperature reached 225 F. Hope this helps someone else out there.
you should have gotten a jet thermostat.....it helps your engine stay cooler since its a high flow thermo
From the factory the ECU does not turn the fan on until 223 degree's and shuts off at 218 degree's. This is very hot, and most cars do not get up that high. A lot of people seem to think there car is over heating but really not.
FU Tuning
Mine does the same thing,i have a scan gauge2 hooked in to watch all the sensors.My fan kicks on at 224, then shuts off after a few min,then turns back on at 224,but after cycling like this it finally keeps the fan on.Just a stupid tune from gm i guess.
I will say if your car is running at the temps to keep the fan comeing on and off, then something else is up. I'm in Fl with hot temps and my car never hit the fan. I have to be in traffic for 15-20 minutes stopped to get that, and usually it hits it cools down and takes another 10-15 minutes to get back.
Maybe a sticking stat.
Edited 1 time(s). Last edited Thursday, October 08, 2009 8:04 PM
FU Tuning
