Rep Power: 0

Did a compression test today, 2003 civic ex, 160k

1: 185
2: 195
3. 195
4. 200

I then added a small bit of oil to the cylinders through the spark plug hole, and retested (I have heard this is a way to detect piston ring failure.)

1: 210
2: 220
3: 210
4: 225

Backstory,
I have been losing coolant with no visible leaks. I am thinking that it is the headgasket, however after this compression test I am not sure what to think?
I drained the coolant and oil and there was not visible mixing of the fluids. It seems that my coolant is just disappearing.

The car will only overheat after 2+ hours of highway driving, and even then only when I slow down or just idle. The fans kick on with the ac, so I know they work.

I'm starting to think a possible thermostat issuse? or bad water pump maybe?

Any help would be appreciated.

Thank you.

 
Rep Power: 811

compression test is not the way to go. when i had a small gasket leak and burning thru coolant, the compression test showed normal all were around 200psi +/- 10psi. if you are losing coolant and it disappears without a leak, chances are very good there is a small leak that seals up once the engine warms up. i never had any overheat or white smoke, nothing. but the coolant would keep disappearing and i did see some white deposits on two of the plugs. and sometimes a minute of misfire when cold starting the car. thermostat and water pump wouldnt cause those problems (unless waterpump is leaking coolant). you could try a combustion gas test on the coolant to see if its contaminated. and if you open the radiator cap and the coolant bubbles constantly for over 30 mins, its def a small gasket leak.

 
Rep Power: 233

Classic symptom of a bad headgasket. Sorry bro.

 
Rep Power: 0

I bought the car recently and was planning on changingthe gaskets, seals, and belts anyway so it's not to huge of a deal. My main concern was that I would replace the headgasket and still have the problem. I'll change it Out and see what happens.

 
Rep Power: 811

when you change the gasket out, make sure and take the head to a machine shop for cleanup, testing, and milling the bottom for a straight edge. otherwise yes if you just replace the gasket it will leak again for sure. most shops (like carquest machine shop) only charge around $100 for "the works" on a head to get it ready to install.

 
Rep Power: 0

no its either waterpump or thermostat, you may have a leak from one of the hoses, hows the condition on the hoses?

 
Rep Power: 312

You can check all the hoses and stuff but 99% it`s the head gasket.