Rep Power: 0

Hello folks - I have an '03 Civic EX with D17 engine, 5 spd and 205k miles.

Been a great car... until the last couple of months. What used to be a very infrequent overheat at idle after highway runs has turned into a very predictable loss of coolant without visible leaking and eventual overheat once the coolant is low.

As long as I top of the radiator every 100-110 miles with coolant, I have ZERO issues. However, the overflow bottle stays full, which is odd.

Compression test- Left to right, facing engine -195 - 167 - 167 - 180
Cooling system pressure test-
Pressurized to 30 PSI. Dropped to 27.5 in 15 minutes.

I have not witnessed the small bubbles in radiator indicative of headgasket failure. There is nothing odd about the exhaust.

It sure seems like a headgasket, but I am hesitant to pull the head until I am sure. How else can I diagnose? Thanks for the help!

 
Rep Power: 519

What I do is similar to a cylinder leakdown test, but I apply full shop air pressure to each cylinder instead of a regulated low pressure.

I use a funnel in the radiator neck, add coolant so the level is in the skinny part of the neck, then pressurize individual cylinders with shop air pressure (170+PSI) and watch for any miniscule change in the coolant level.

(You can probably just fill the coolant up to the skinniest part of the rad neck and watch for it to rise and spill over, instead of using the funnel.)

This has not failed to reveal any breach for me yet, but the test may need done on both a cold and hot engine (If it doesn't show the problem on a hot engine, then try it cold later).

HTH

 
Rep Power: 314

^ Hmm.. to those that don't have access to shop air at 170psi you will need to check for exhaust gases in the coolant system. It's a pretty simple test you just need to get the proper tool which you can probably rent. However, an overflow that is filling up generally means your head gasket is gone