Engine Cooling problem
1995 Honda Civic Automatic 116000 miles
I have a 1995 Honda civic DX coupe with 116K miles on it. Bought it about 15K miles back last year. About a couple of months back, I had gone out of town. It was a hot summer day, so the AC was on and there was a lot of uphill driving. The engine started heating up. I let the car cool down, checked the radiator and the resrvoir and saw it was very low on coolant. So bought coolant (Zerex pre-diluted, which mentioned Honda as one of the brands it would work for) from a gas station, and topped up the radiator and the reservoir (to the MAX level). Drove back home (about 50 miles), and there was no problem.
After that, for the next 2 months or so, was driving only in town (I live in a small town, so even the longest drive is maybe 5-6 miles at a stretch). No problems with overheating or anything.
Then last weekend, I was on a long trip again. Another hot day. Was on the highway and it was fine. We didnt have the AC on, and the windows were rolled down. Took an exit for some coffee, and the temperature gauge started climbing up. Checked the coolant level and it was fine (in fact coolant in the reservoir was above the MAX mark). I noticed that the cooling fan wasnt working. So I assumed that was the problem. Let the car cool down, continued with my trip on the highway. The temperature was OK as long as I have driving at 55 and above.
But an hour later, when the traffic slowed down due to road work, the gauge started climbing again. Luckily, the traffic didnt last long, so we were back at high speed and the gauge went to below the midpoint. Whenever the car overheated, I would pop up the hood and the fan would usually not be working.
So I googled fan troubleshooting tips and found advice on several forums. Took the connector off, shorted the pins and the fan started running, so the fan motor was OK. One possible reason being mentioned was thermoswitch and/or thermostat being bad. It was mentioned on a couple of forums that I should check to see if the lower hose was cold. It was not. After keeping the car in idling for 10 minutes, both the upper and lower hoses were hot. The upper one was hotter, but the lower one was hot too. So I took this to mean that there probably wasnt a problem with the thermostat or thermoswitch.
Next, I read that air pockets could be stopping the fan from coming on, so I should purge the system. Did that. Fan came on twice while the car was in idling with the reservoir cap open. So I thought now that the fan was working, things were fine.
Took it for a test drive. Took an exit and slowed down after 45 mins of driving, and there we go again. The gauge started climbing up. Popped open the hood, and saw the the fan was actually working. Both the lower and upper hoses were warm (though like I said, the lower was was a bit less warmer). Yet the gauge kept creeping up. Drove back again, maintaining high speed and the temperature remained fine.
So here are my questions -
1. Is it still possible that something is wrong with the thermostat or thermoswitch? The fan is coming on now, and the lower hose is not cold. I read somewhere that if the thermostat is busted, the engine will pretty much start overheating in minutes, and won't cool down even if you are at high speeds. Dunno if this is right.
2. There are no visible leaks. The coolant level is fine. I dont see any leaks from the water-pump either, but could that be a problem?
3. In general, what else, apart from fan problems, could cause this intermittent at-low-speeds-only overheating? Wherever I saw people saying that they had this problem, the people responding invariably said it was a fan problem. But now that the problem is occuring despite my fan running, what else should I check?
I am taking the car to a mechanic today for a diagnostic check, but would also appreciate some inputs here in case he cant figure it out.
Thursday, February 8th, 2018 AT 1:01 PM