Last week during a hot/long day on the road, my engine temp gauge started fluctuating between 1/2 and almost 7/8 on the gauge. The weird thing was that it was fairly stable most of the time, but every 10 minutes or so, it would heat up, and spend bout 15 seconds at the high mark before dropping down again. It didn’t seem to be related to rpm, A/C operation, or driving intensity. When I got home, and let it cool down, I checked the coolant level. I couldn’t see any coolant in the radiator, but the expansion tank was nearly full. I guess the low coolant level can explain the symptoms above, but I can’t figure out what is happening to the coolant.
I took the car to a mechanic and had a pressure test, which didn’t show any leakage. I had a new thermostat and radiator cap installed. They flushed the system, and tested the hose between the expansion tank and radiator. After driving the car home, the coolant in the radiator had already dropped to the point where I couldn’t see it, and the expansion tank was 3/4 full. So, I guess the $350 I just spent was in vain. Now, I am planning to keep track of the levels of both reservoirs (and refilling the radiator of course) to see if the fluid is leaking, or if it is just not returning from the expansion tank. Hopefully this bit of knowledge should help locate the problem.
The successful pressure test leads me to believe that it isn’t leaking externally. However, I’m wondering if there is a small enough leak that wouldn’t be detected by the pressure test, but is significant enough that it would allow air in when the engine cools instead of pulling the fluid back from the expansion tank.
Anybody see anything like this before?