Other potential but not nice is hole in water jacket ie walls.

 

As above really. He said they checked for gases in the coolant, and pressure tested the system. Everything was ok.

 

As you know I'm mechanically dyslexic! Can you elaborate what this means and how you'd check it, please?

 

^^^ Cracked barrel below piston ring travel in the bore.
It may act like a pump.<and may not show gas in the test>

Any water in your oil <could drain and refill with the oil taken out <just to check it>

That's after jacking the front up for re bleed btw ..

 

simon, as i said to you (a couple of times ; p ), i had the same issue, even when they took the head off and checked it sait it was flat, had the tiniest bit skimmed off, changed the head gasket for a cosworth one and it was fixed.

might be time to speak to someone to whip the head off?

 

Yeah, if it's pressuring up like that (and quickly, presumably) there's only really one source of (brake mean) effective pressure that could be causing it.

I cannot understand why it wouldn't show up on a sniffer or pressure test, though. Maybe only leaks in VTEC?

 

Bled the system this morning and had a 10 minute pootle to town. Temps where they should be (around 88-90C).

I'll keep an eye on it, but it does seem to be worse when VTECing a lot i.e. track days.

I do have a list of things that need doing once my new run around arrives, and it'll be off to TGM for this and the rest of the list.

Thanks again, all.

 

I had similar problems with mine.

Getting through coolant at quite a rate, but no leaks under the car. Occasional steam from expansion bottle in traffic, then overheating, big problems, check coolant level and there's nothing there.

In the end, I'd bled, re-bled, faffed and generally banged my head against a brick wall. So when the MOT and service came due, I gave it to my local trustworthy independent place and asked them to find the leak, which they duly did.

It turned out to be the thermostat gasket - £11 of part and £110 of labour, would you believe... They had a pig of a job finding what the issue was. It only leaked when up to temp and at high-ish revs (or up to temp and with the pressure testing gizmo on it).

The difference between your experience and mine was that on some days the expansion bottle would look full and on others it would be bone dry.

The failure mechanism appears to have been initially an inward leak at the thermostat housing gasket, the air then expanding as it gets heated and pushing out coolant into the bottle. As the level drops, this changes to hot air/steam being bubbled through the coolant in the bottle and boiling it away (hence the steam from the front of the car).

The garage said that when they got it hot and pumped up the pressure to find the leak, all was fine initially, then it went catastrophically, making it super easy to find, albeit it was not easy to get at!

All in al, service, MOT, fault diagnosis and fix for a smidge over £300, so I'm happy.

 

Get a sniffer test done on your coolant. If it comes back negative, that'll be the expensive things dismissed.

It does seem to be an air bubble trapped.

 

Not got a inlet manifold coolant bypass on it by any chance,
just a thought !!