Mechanics

OVERHEATING - CAN'T FIGURE IT OUT

1998 Honda Civic

Engine Cooling problem
1998 Honda Civic 4 cyl Front Wheel Drive Automatic 223000 miles

So there are a few factors that I think may contribute to my 1998 Honda Civic EX and the overheating problems that I am having. Here is a detailed history of the problem from when it first began to occur:

1) About a month ago, the water pump went out on my car. It began to overheat, even on cold days. Also, the heat in the car stopped working around the same time that the water pump broke. After one or two times driving the car (and it overheated within 5 mins) I realized it couldn't be driven anymore. The timing belt and water pump and gaskets and seals were all replaced by a certified mechanic. The car seemed to run perfectly fine around town.

2) About a week ago I was making a 2 hour drive at highway speeds (65-75 mph) and noticed that the temperature gauge began to fluctuate between normal and hot. As it was on " H", I pulled over and opened the hood to find that the overrun reservoir had boiling coolant, but no leaks just a bit of steam. Without accelerating or idling, the gauge continued to fluctuate. The heat in the car also continued to not put out any heat (or at least very little warmth). I finished the rest of the trip without a serious overheat, but the heat gauge constantly fluctuated from normal to hot temperatures moving up and down quite rapidly.

3) I replaced the thermostat. Still not blowing any hot air, I have no heat. The gauge continues to do the same thing. The fans on the radiator are turning, the water pump and thermostat are brand new. The head gasket is not damaged (as there is no oil in the coolant or visa-versa).


I was told it could be my heating core, but that would not explain the problem of overheating. It may explain why I have no heat, but I've been told that the overheating is being caused by something else. I am absolutely stumped, and I don't have the money to experiment and keep buying parts that aren't going to fix my car. Any ideas what the problem might be?
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Shagadelic
January 12, 2010.




Hi Shagadelic,

Fluctuating temperature readings and heater not working correctly are usually caused by insufficient coolant in system. After replacement of the water pump and later thermostat, was the system bled of air?

Do you have coolant losses at radiator with the recovery tank overflowing at times?

For the head gasket to be bad, it does not necessarily mean there must be oil in coolant or coolant in oil. The head gaskets are of the metallic type so it would not leak badly to cause thus.

With cold engine, remove the radiator cap and cehck the coolant level. If it is low, top it up and with heater turned to maximum, start engine. Top up coolant if the level drops and when coolant level stabilises, close radiator cap and bleeding should be complete.

When the head gasket is only slightly bad, it might take quite a bit of running before coolant losses are detected. If you run the engine for short periods, it might take a few days before you are able to notice any coolant losses.

KHLow2008
Jan 15, 2010.
Hello KHLow2008,

Thank you for the advise. After installing the new thermostat the air was not properly bled out of the coolant lines. I followed your directions to a " T" and bled the coolant lines. I even tried it one more time just to verify that there was no air in the lines. This fixed the problem that I was having with my car overheating, and the temp gauge bobbing up and down, however, I still have no heat.

Since my last post, I have driven the car on quite a few long trips, and quite a few short trips (about 1,500 miles). There are absolutely no coolant leaks, as it is topped of and remains that way.

The car is running perfectly, with the exception of no cabin heat. There have been no overheats, the temp gauge is working properly. After the car is warmed up and at normal operating temperature I get a VERY SLIGHT bit of heat, but not nearly enough to heat the cabin. To be honest it is hardly noticeable that that heat is on. But about two months ago, the heat worked TERRIFIC. If I turn the heat completely off for a few minutes while the car is running, and then turn it back on I get a surge of warm air for about 30 seconds before it becomes cold again.

Oh yeah, I also checked the heat/cold valve and verified that my heat/cold lever is properly working, so the valve isn't stuck. And when I turn it to cold the air does get slightly colder, but the heat is still not working. I have also check the upper and lower radiator hoses and both of them are getting hot. Does it sound like it might be my heating core?

New thermostat. Fans work. Coolant system has been bled. New water pump. Both radiator hoses are getting hot. Still little to no heat. What have I missed?
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Tiny
Shagadelic
Jan 31, 2010.
From the latest information provided, the cooling system is good with no coolant losses so we have to get to the heater problem.

When heater is turned ON, are both heater hoses hot?

Does the control valve open fully?
Are the air mix door and control valve cable adjustment correct?

KHLow2008
Jan 31, 2010.

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