Honda civic overheating no apparent reasons, confusion

It seems as though my car can’t be fixed. I have a Honda civic 03 with 150k on it. I have taken it to several mechanics, I fell into the trap of throwing parts at the car by the recommendation of mechanics. First a mechanic thought it was a bad radiator, but it still overheated. Then, I took it to another mechanic who said he couldn’t get it to overheat then tested it with the chemical test (negative) and tested the cooling system and thought it was a bad thermostat, it still overheated. Burped the system, nothing changed. They determined it was a pinhole leak in the head gasket and that it would need to be replaced.I was weary about this so I took it to a master tech to examine it, he determined that it was a bad head gasket, yet he didn’t explain how he knew this. So I found a trusted repair business (been in business for years, great ratings everywhere) quoted me around $1000 to get a new head gasket installed (including possible milling/re-surfing). This mechanic is detailed about every aspect of investigating/diagnosing the problem and is very precaution about installing a head gasket, trying to save me money and future hassles. He told me over the phone that they can’t get it to overheat after hours of letting it run and some driving, this is the odd part it doesn’t seem to overheat when stationary, only after it has been driven for awhile. He did a hydrocarbon test (negative again) and no pummels of white smoke, although I’ve heard this isn’t always a sure sign that it isn’t blown. I told him that it has overheated on me several times before, I told them that the car needs to be driven for awhile. For example, when I drive it to school about 60mi for 45 minutes it overheats and I have to stop and pour in antifreeze. It seems to overheat after about 60mi especially when I stop after the trip and start idling in traffic. What is going on here?

they are going to keep it till Tuesday and see if they can get it to overheat.

If the vehicle has an automatic transmission, there’s a transmission fluid cooler located inside the radiator.

If the transmission starts to run hot, this can cause the coolant in the radiator to start to run hot which then causes the engine to overheat.


It’s automatic. You think it’s the transmission fluid cooler gone bad? I think it might be that I had a bad radiator installed but idk. When I got this car it overheated, took it to the mechanic got a new radiator installed and it began overheating again. So maybe the original problem was the radiator and I just got two bad radiators installed?
I heard it could also be a bad water pump but there isn’t any way to tell these things it seems, unless its’s opened up.

You don’t understand.

There’s a transmission fluid cooler within the radiator.

If the transmission is fluid is overheated, it overheats the coolant which then causes the engine to overheat.

So, it doesn’t matter if you switch out the radiator or not.

If the transmission is overheating the engine will overheat.

And vice-versa.


If the transmission is overheating, could a separate transmission cooler be added to take the load off the radiator? This would be a stop gap measure.



How would one first determine this and fix it?

One would take an infrared temperature gun, and point it at the transmission fluid cooler line going into the radiator to see what the temperature of the transmission fluid is.


A separate transmission cooler isn’t real expensive.

Interesting. I wasn’t sure what a transmission cooler was actually until now. Is that something which would exclusively heat up when driving and not stationary? that’s the odd thing about this that the mechanics keep saying, it doesn’t overheat while stationary for hours but driving after 45 it does.

That’s because with Honda transmission, unless it’s put into gear, the pump within the transmission doesn’t operate to build pressure which doesn’t create heat.

In order to do fluid exchange on a Honda, it’s required to put the transmission into gear so the pump engages to pump the old fluid out so the new fluid can be added.


Another thing is I hear this intermittent squealing noise when it’s cold or moisture in the air. Heard this could be due the idler pulleys going bad which would take out the belt and cause it to overheat. Also heard the squealing noise could be due to my water pump?

Or worn out serpentine belt?

If the belt doesn’t look worn, it probably is.


I don’t see how it could be the head gasket at this point because there is no milky dipstick, no pummels of white smoke and came up negative both times with the hydrocarbon test. The car just overheats for some reason then the coolant is forced out the reservoir. I guess if it was a pinhole leak or a blown head the coolant would just leak into where the oil is and then blow out as white smoke from the tailpipe, right?. I go through so much antifreeze that it seems impossible that it could be the head gasket because the tests would come up positive.

Overheating is a condition where you want figure out the cause as soon as possible.

Because, continued overheating damages the engine/transmission.


I just wish I could figure this out. With what I said above how could it be the head gasket? just wondering your opinion. Could it be a head gasket when i’ve put tons of antifreeze into it but no milky dipstick, white pummels and came up negative twice with a hydrocarbon test.

Could it be a head gasket when i've put tons of antifreeze into it but no milky dipstick, white pummels and came up negative twice with a hydrocarbon test.


@insightful how?

Just a question but how do you know it is overheating? Do you have a temp gauge or just a light going on. If you have a gauge is it a gradual climbing of the needle into the red zone or more immediate.

Also the usual suspects like lower radiator hose, water pump or internal blockage.

It may need an alignment check. If toe in or thrust angle is way off it will cause both engine and transmission to work too hard. See if the air dam is still attached under the radiator. There’s so much more to check on.