2000 Civic LX, Automatic, 220,000 miles. On the way home from work Monday, I noticed the temp gauge was creeping up to H while sitting at a red light. Started moving and it dropped. I drove about a half mile until I could pull over. Popped the hood and the electric fan came on. Temp was creeping up again. No visible leaks that I could tell (road was damp so almost impossible). I gave the car some gas and revved to about 3,500 RPM and in just a few seconds, the gauge dropped to normal. I mean dropped, like you flipped a switch. The rest of the way home, it stayed at the normal position and the fan was off. I popped the hood at home and before I could get it open, the fan came on again and the temp started creeping up. I revved it up again and held it and the same thing; temp dropped like flipping a switch. I turned the car off and had supper and then plugged in my OBDII bluetooth adapter. I wanted to rule out a faulty gauge. The car got to 215ish and the fan came on. It kept creeping up to 235. I gave it gas and it immediately dropped back to 215ish, within 10 seconds and stayed there as long as I kept the revs up.
I haven't had time to look at it anymore but I'm taking a half day at work and going to look into it. I'm starting with the thermostat. I'll remove it and check it on the stove to see if it's opening. Meanwhile, I thought I'd run the car to see if it overheats with the thermostat out. It's due for a timing belt/water pump in the next 10,000 miles (last one was at 135,000). If it overheats with the thermostat out, it almost has to be the water pump or a head gasket failure right? Is there anything else anyone would recommend looking at while I'm checking?
To add: I had a heater hose fail about 20,000 miles ago and while I had the system drained I replaced the thermostat (Advance Auto, could be the problem) and flushed the system with distilled water until it was clear, then added 1/2 the total capacity of full concentrate. If it is more than just a thermostat, I'm probably not going to fix it. I have 4 vehicles and this one is just my beater/spare. The wife will cry, as it's her "baby" (but she drives the CR-V, go figure) but we really don't need it. Any advice is appreciated.
I haven't had time to look at it anymore but I'm taking a half day at work and going to look into it. I'm starting with the thermostat. I'll remove it and check it on the stove to see if it's opening. Meanwhile, I thought I'd run the car to see if it overheats with the thermostat out. It's due for a timing belt/water pump in the next 10,000 miles (last one was at 135,000). If it overheats with the thermostat out, it almost has to be the water pump or a head gasket failure right? Is there anything else anyone would recommend looking at while I'm checking?
To add: I had a heater hose fail about 20,000 miles ago and while I had the system drained I replaced the thermostat (Advance Auto, could be the problem) and flushed the system with distilled water until it was clear, then added 1/2 the total capacity of full concentrate. If it is more than just a thermostat, I'm probably not going to fix it. I have 4 vehicles and this one is just my beater/spare. The wife will cry, as it's her "baby" (but she drives the CR-V, go figure) but we really don't need it. Any advice is appreciated.