Friday night my check engine light came on, but I experienced no change in the feel of the car, performance, or engine noises. The car operated without change for several hours until I was driving home, then it began to overheat. I pulled over the car, checked all fluid levels (they looked fine), and when I got back in the car the check engine light was now off. The overheating issue persists, however. The needle is usually just below the half-way mark when the engine is warm, but it begins to creep up now, coming to rest at about 85% to the max mark. If I rev the RPMs to 3.5-4 x1000, the needle will immediately fall down to about half way, and then begin creeping up again (probably takes less then two minutes to go from half-way to
85%). Sometimes the car runs fine for hours before this starts, sometimes it starts minutes after the car warms up. Sometimes it will be overheating, and suddenly cool down and be fine. I just noticed this last night, and it may be coincidence, but it seems that as long as my heater is on full, the engine will be cool, and if I turn off the heater, or move the slider all the way to cold, the engine overheats again. While the heater is on, the air coming out is hot (possibly hotter then it was before, but maybe I'm imagining that). It seems like the kind of problem you would remember if you've run across it before, so I'm hoping someone can help. I had the water pump and radiator hoses replaced about a month ago.
Thanks.