I have a 1999 Honda Accord, my engine is heating up when the car is not running, I recently replaced the thermostat thinking this was the issue however the problem continued. I checked for any leaks and there is none, I do need to replace the catalyc converter, I don't know if this issue has any relation with the the engine overheating. Any clues? please let me know.

 

I've moved this to General Tech.

What is the car doing. You say heating up when off. The science will say yes that is true but I'm guessing there is something going on.

At the same time you talk about overheating. I'll assume when the engine is running.

Need a little more information - also is this a 4 or 6 cyl.

 

How do you know the car is overheating when turned Off? Are you watching temp gauge w/ keyswitch On?

Cooling fans should come on w/ engine off (earlier models to 97 for sure, but less familiar w/ 99) to prevent temp from rising above 225F. This heating would still show as a significant temp increase and is normal. All cooling systems get hotter when engine is turned off and heat from combustion soaks the engine warming the non-circulating coolant (slight circulation due to convection).

good luck

 

Check the fuses for you cooling fans, they should be in the fuse box under your hood but could be inside the car. Also hook straight power to the fans to see if the motor is still good on them.

 

Thanks for your help, sorry for not being to clear. I meant was when the engine is on, when the car is moving temperature is normal, if I stop at a red light, or traffic jam on the FWY temperature starts rising and goes back to normal when the car starts moving again. The main issue I think I have is the radiator consumes the water too fast, I have to put water every 3 or 4 days, When I filled it with water it works fine but 3 or 4 days after the water level is low is when the car starts heating up. I checked for leaks and no leaks at all.
Car model is a '99 accord LX, 4cyl, manual transmission.

 

That's typical behavior for a car that's low on coolant: OK on the highway but a rising gauge at idle.

The water is going somewhere. External leaks are sometimes hard to find if it's a pinhole leak and the coolant is evaporating before you can see it. Another possibility is an internal coolant leak. A cooling system pressure tester is a good way to find pinhole leaks. Auto parts stores loan them out.

 

X2 - There is a leak somewhere, find it.

Thanks Roader