For the past month my car has been overheating.
It happened the first time on a long drive about 5 months ago and never happened again until 4 weeks ago. The car overheated at the end of an hour long drive to DC when I got to my destination I poped the hood and checked the coolant level and saw that the coolant was a brownish color so I figure the worst (bad head gasket or a crack). The not overheat on the way home from DC. After that I made an appointment to take it to the shop. For the next few days (one or two long drives) the car does not overheat.
The shop guys take a look at it and do a leak down test and a carbon test. They spent a while letting the car run and test driving trying to figure out what was wrong. They found nothing wrong and the car did not overheat. I asked them about the suspected oil in the coolan and they said it was just a little dirty but it sure looks brown. The following day I drive to DC and the car overheats on the way home.
Now the car is overheating almost every time I drive it over 30 minutes. The temp slowly starts to go up and then once it is just past the illustration for the thermostat I turn on the heat full blast and within a few seconds the temperature returns to normal. Some times it will go back up some times I can turn the heat off and the car will be fine for another 15 min.
If i am traveling down hill and the car overheats I have tried putting the car in neutral and coasting (at about 60mph) and I have noticed the temperature go up. It seems to cool off the best with the car in 5th gear at 58 mph (~2500rpm).
If the car is overheating and I come to a stop occasionally the thermostat will slightly pulse up and down.
Oh and when the car is overheating I have stopped to check if the fans are running and they are.
I would prefer not to put any money into this car but I need to wait 1 to 3 months before buying a new car.
My thoughts now are to replace the 'dirty' coolant, the oil, and the thermostat and hope it fixes it or lasts a few more months.
Any one have any other ideas on things to check?
Thanks for the help,