crazed4macs

Hey guys, new to the site and looking for some advice. I'm hoping the information I provide is ample to begin possibly diagnosing a problem. Car does not overheat at idle, fan is working. Temperature begins to rise after about 20 minutes of highway driving. Flip the climate control to heat and engine temperature returns to normal. I've pressure tested the system and carbon monoxide tested for head gasket. Holds pressure and no exhaust is leaking into the coolant. Started with thermostat, changed out with 170 degree oe replacement. Problem persists. Coolant resevoir seems to get low rather quickly, and I have hot heat. Water pump? Any suggestions would be awesome. Also a 98 ex.

Cheapshot1979

Crazed,

#1 Since you replaced the thermostat, did you idle the car with the radiator cap off to force air out of the system? Once bubbles are gone drive the car and get the thermostat to open to pull coolant into the motor. This could in turn show that you have low radiator fluid thus needing you to add more coolant. Don't add it to the coolant reservoir, add it directly to the radiator. Once system is free of air bubbles, add coolant to the appropriate mark on the reservoir bottle.

#2 If the water pump has failed it could be that the motor is overheating and boiling the coolant off, thus showing low coolant.

#3 What type of coolant are you putting in your motor?

#4 Have you tried flushing out the radiator?

crazed4macs

Yes, I did idle the car with the cap off long enough to trigger two fan cycles as per the manual. Topped off radiator and filled reservoir to max mark. Drove it for about thirty minutes and all seemed well. Right now, I'm using water to replace what I'm loosing because it's so frequent. I have not tried flushing the radiator. I noticed this morning, after I topped off the radiator and reservoir that my heat isn't nearly as hot as it once was..

Cheapshot1979

Alright, so sounds like the thermostat that you put in is operating correctly. Next I would look at the one of three things.

#1) Flush the radiator and the motor

If the anti-freeze channels inside the motor are plugged, it could cause the coolant to move slower through the motor and cause it to overheat.

#2) The heatercore

If the heatercore is bad, sometimes the heatercore will actually leak inside the cabin onto the passenger side floorboard. If you are smelling anti-freeze inside your car I would pull the glove box out and start looking for leaks around the heatercore. Your carpet may also be damp or wet depending on how bad the leak is.

#3) Bad headgasket

The most common headgasket failure leaks externally, so it is usually clearly evident. It is however possible that the headgasket could also have failed internally, allowing coolant into the cylinder or into an oil channel. Pull the oil dipstick and look for discoloration of the oil. If the leak is small enough it could be burning off inside the cylinder as well.

Once you have actually tracked the problem down, I would put the correct thermostat back in as well.

Hope this helps, if it doesn't then i'm at a loss. Cooling systems are pretty simple, not too many options left after that.

crazed4macs

Thanks a lot. I appreciate all the feedback. I'll try flushing the system and poke around for other symptoms. Like I said, I had a honda mechanic pressure test for leaks and carbon monoxide test the radiator for a head gasket. Everything checked out there, thermostat was an easy cheap way to start attacking this thing. He was pretty clear he didn't think it was a head gasket as they get them quite a bit. Once I have it nailed down or uncover something unusual, I'll get back with some info. Thanks again.