JacobD

Hi everyone, I'm looking for any advice I can get here.
2005 1.7L 5 speed manual.

Coolant is being pushed into my reservoir tank but not flowing back into my radiator.
This only seems to occur at highway speeds (3000 rpm ish) for extended periods of time.
Driving 2 hours or more on the highway is almost guaranteed to overflow my coolant reservoir, whereas driving to and from work (10 minutes on the highway at a time) my car will last two weeks before the reservoir is filled and I need to recharge my coolant.
After a while, my heater core stops pushing cabin heat.
My car has begun to overheat twice so far. Each time I've caught it very quickly, pulled over, and been able to recharge my coolant.

Here's my current diagnosis:
This is being caused by gas (exhaust gas or something else) entering my coolant somehow. It fills up the heater core first (highest point), displacing coolant into the reservoir.
Over time the air pocket grows and eventually it causes a full air lock that stops coolant flow, causing the car to overheat.
I know my coolant is building air pressure because even when cold, opening my rad cap releases air and bubbles coolant out. If there were no air, there would be very little pressure in a cold system.

I believe this is caused by a leaking head gasket. BUT...
There are no other symptoms of a leaking head gasket. My oil is perfectly fine (no coolant in the oil), my coolant does not show any signs of oil shimmer, my exhaust comes out perfectly clear, and when running with the rad cap off, there are no constant bubbles appearing. (There are usually a few, but I believe they're the air pocket clearing itself).

History:
Four months ago I replaced my timing belt and water pump. I do not think I charged my coolant effectively after the timing belt job, and it caused my car to overheat a few days later.
This MAY have caused a failure which is now giving me these symptoms.

What I have done so far:
I've changed my rad cap and thermostat. A faulty rad cap could let coolant out but not back in. This doesn't really explain where the air comes from, but it's worth a shot since it's cheap.
A faulty thermostat could be causing the overheats and giving me some weird symptoms. The new thermostat seems to be operating properly.
I've taken my car into my mechanic friend, where we ran a handful of tests.

• Each cylinder passed a compression test. Lowest was 185 psi.
• Rad holds pressure
• Rad holds vacuum
• Block test kit (blue fluid bubbler) passes over and over again.
• The engine is not giving any codes while driving. No misfires, nothing out of the ordinary.

His diagnosis was "The only thing I see it being is a really bad air lock".
I don't agree with it. We charged the rad under vacuum and the problem recurred in 2 weeks. If it was a bad air lock, the air would expand under temperature as soon as the engine is hot and push the coolant out immediately each time.
An air lock also wouldn't be more or less affected by long periods of highway driving.

I've strained my mind over this, and the only thing I keep coming back to is the head gasket probably has a very small crack in it that only expands under full temperature and high RPMs
The water pump runs faster, pushes higher pressure, forces the crack open more, and we get exhaust gas entering the coolant.

However, I've tried the block test kit over and over and I can't get it to fail. I've even tested the indicator fluid on raw exhaust gas and it turns yellow, just to make sure I don't have a bad batch of indicator fluid.
Something is clearly wrong with my Civic, but I can't find out what, so I can't fix the issue.

If anyone has had similar experience, or sees something that I might not have tried yet, please let me know.

Thank you!

Zedt3

Headgasket is the issue. Stop wishing on fairies and pixies. That's the problem, always is the problem with these engines.

Fix it or sell the car.

pcbabb

iTrader: (3)

I second the headgasket. VERY common issue on d17's

brijar92

JacobD, did you get your head gasket replaced? You were going to let me know how the job went.

Thanks,
James

JacobD

Changed the head gasket one month ago. Symptoms seem to be gone.

brijar92

Thanks Jacob, congratulations. I'll be giving this a shot soon myself.