Dangerousjordan

01 Civic LX, 157k, auto with an allegedly new radiator from previous owner. New cat from me. It WAS overheating at random when idling until I put a new multiplex control unit in. But now it can idle indefinitely with no problems. However it still will overheat on the freeway at higher speeds. It gave off a p0128 code. Nobody with that code has mentioned overheating yet...

Thanks guys

ezone

Radiator can't shed heat, or the heat isn't getting into the radiator.

Low coolant level?

Thermostat that can't open all the way?

Are the condenser fins full of bugs and debris? Maybe it needs a good washing. Lean the radiator back so you can get a hose nozzle inbetween and blow everything toward the front of the car.


Usually a thermostat issue......But could be a coolant temp sensor, or the overheat problem is related to it.....and if nothing else solves if, there is a reflash for some 01-02 Civics for that code.




I'd probably look hard at the thermostat and coolant level first, those are easy.

Dangerousjordan

Thanks, whenever it gets too high I have to add coolant, presumably due to the radiator cap doing it's job. All to say the coolant is high enough.

ezone

If you keep having to add more coolant, you have a serious problem.

Plus, overheating leads to head gasket problems, and that engine already has head gasket problems to begin with.

Dangerousjordan

Interesting update... The thermostat that was in there had been modified to flow freely, no spring or anything, just the least needed to sit something in there. Now I'm even more confused as to why it will randomly overheat on the freeway... Anyways I installed a new one from Napa. This does however explain the pending code that has to due with not heating up by a certain point.

ezone

See if it still overheats on the highway now that you have a stat in it.....and if it does then you need to monitor what else happens at the same time.

Does it stay normal until the radiator gets low, THEN it overheats?




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Now that you have a (hopefully) working thermostat, you need to:

Fill the radiator and burp it thoroughly as per usual FSM instructions.
Fill reservoir to the MAX line and mark it if you wish.
Let engine cool down, refill reservoir to MAX line.
This level should become stable and consistent after a couple warmup and cooldown cycles.

The level in the reservoir will change with engine temperature changes but it should always return to the starting point when the engine is cold.

The system is designed to keep the radiator completely full at all times.



If it overflows the reservoir and the radiator gets low, then you're probably looking at a head gasket.
If the head gasket problem is the typical very slow leakage it might take several hundred miles before enough coolant is displaced out of the radiator to make it run hot..... but at the same time the reservoir level would be slowly creeping upward as liquid is displaced, so check it every morning before taking off.

Dangerousjordan

Overheating issue appears to be solved by the new thermostat. Thanks guys. I've got a 2 hour drive ahead to confirm this but it handled a 45 minutes drive through hills on the freeway like a champ last weekend so I feel pretty confident.