Head cracked???
 

OK so the symptoms I'm getting are pressure in the cooling system after literally cranking the car for 5/10 seconds without firing up. (which only happened because the iffy accordion hose came off the turbo again) Not enough pressure to make the hoses hard, but pressure nonetheless & I'm thinking if a HG was leaking that badly there'd have to be coolant burning (not happening), and also after the engine'd run for a few minutes it would end up blowing a hose off or forcing all the water out of the cap.

This is not happening & in fact once the car's started and begins to warm up the leak appears to get less and less until once up to temp & burped, you'd swear there was nothing wrong. This is making me wonder if there could be a crack in the head which is opening up when cold allowing the compression loss into the coolant & closing as the head expands thus reducing the symptoms.

I'm pretty sure it's not just an airlock as I've burped it a couple of times & had the heater working nicely, plus how would the cooling system get pressurised without any heat if it were an airlock? That & there's the bubbling sound from the heater on startup sometimes...

Now, bearing in mind that the car has had a complete refurb. on the head could it be that the gasket was simply installed badly & is causing this (why would a blown gasket get better with heat?) or could the head have cracked?

Either way I'll be stripping her down & finding out for sure but I was just wondering how prone to cracking between a combustion chamber & water jacket the heads are & if it's really worth me having the thing crack tested or just re-skimmed, fit a new gasket & hope for the best?

Cheers, Dan. :confused:

Quite simply, you won't know until you get the head off the block and look. A bad HG is still just as likely. It is possible that you are burning coolant and it is also possible that the hole is small enough that combustion gasses are getting pressed through but there's too much resistance for coolant to come through at this point. The reduced pressure as the car warms up is only indicative of a small leak and that as the head, block and HG expand from heat the leak that is being pressed closed enough seal sufficiently.

At this point don't worry about it, it's pointless and it's distracting.

I guess you're right, whatever happens I'm still having the car & whatever it turns out to be is whatever I'll fix.

Just one thing, I did a compression test last night (cold as that's when the problem seems worst, I'll do hot today) and all came back at 145psi except number 5 which was 130psi, exactly 10% so just about within "acceptable" range & not what I would have expected from such an apparently big leak.

I think I'll look into sealing products for the moment (such as K-seal, which is designed with bi-metallic engines in mind) and if the problem persists I may run something like that through the cooling system to try and stop further erosion of the gasket/head.
At least that way I can get some use out of the car & identify/correct any other issues before spending big money on the motor. (If I have to do the HG I'll probably get the head & block lapped & go with the MHG solution with ARP bolts, that way it should last a bit better & I can tune without worrying too much...)

Don't start pouring in "sealants" everywhere... they can cause a lot more trouble than they help and generally, they only serve to hide symptoms of much bigger problems. There is no magic cure and it's not worth putting even more components at risk.

A compression test when the engine is completely cold could be thoroughly off. Number 6 may be sealing just fine but it may need to be a bit warmer to do so... it's not uncommon and that is why they say to test it warm.

I'm getting confused... so many people with projects... I thought you were in the process of doing the HG?

No I'm the one in the process (now completed, yay!!!) of swapping an old Mitsi Pajero for an "abandoned" MA70 which had already had a full rebuild, minus new turbo... :)

Anyhow, progress report-: Done a hot test which came out as all being 155-160psi & so in theory all good. Also given it a thourough bleed through with the front raised off the ground a good 15". The thing is though, there's still a constant stream of tiny bubbles coming through (creates a foam that looks like the inside of an Aero bar!) into the rad top.

I wasn't about to put sealer in willy-nilly, was just considering trying this if the compressions were showing a BHG simply to get some use out of the car to find any other faults before stripping the engine again, as the comps. seem fine I'm not going down this road.....yet...

Anyway, the compressions being good & no smell of exhaust in the bubbles (plus the discovery that the cooling system only really seems to gain pressure over & above water expansion when the turbo spools up) leads me to wonder if a worn turbo could potentially leak boost into the coolant, seeing as it's partly water cooled?
The turbo is pretty worn, with more play than I think there should be & some impact damage to the vanes. So could this be the case I wonder?

EDIT-: OK I just looked over a cutaway view of a 7M-GTE which showed a cutaway turbo & from that (not brilliant) view, it doesn't look like there's any possibility of boost being transferred from the compressor cartridge to the coolant. I could be wrong & hope I am because replacing an already worn turbo would be a lot less painful than doing the HG & then still having to find the cash for a new turbo anyway... :barf:So, anyone know definitively if a worn CT26 could leak boost to coolant?

No, unless the turbo housing is cracked, the coolant passage is sealed. If you're getting more air pressure in the coolant system when you boost it's probably the HG. Get the pH tested.

What's an Aero bar? N/m, it's on Wiki: http://en.wikipedia.org/wiki/Aero_(chocolate)... See... I can look things up! So, which kind/flavor does the foam look like? If you've got foam in the coolant, it's contaminated. Clean water doesn't foam and anti-freeze additives are formulated to prevent foaming. You should check your oil, if there's anything that looks like chocolate pudding it's contaminated as well (look under the oil cap). If it is just discolored the coolant could be loaded with rust, but I've never known rust to cause foaming.

Even if the compression were still looking poor I'd recommend against using any form of magic block & gasket sealant.

Yeah that's what I thought from the cutaway pic, still there was some hope there...

There's no obvious cross-contamination of oil/coolant although a small amount could well be getting transferred.

I'm more or less 100% it's BHG now anyway as the coolant's started showing tiny flecks of silvery metallic & brown fibrous bits that look to my eye like tiny pieces of head gasket. :yum:

I'm going to do a chemical test if I can get hold of the stuff from my dad's work (I'm not paying for it now I'm convinced it's only gonna tell me one thing!) and if not then I'll just bite the bullet & start ripping the motor apart again. On the positive side, at least this'll give me a chance to see first hand how well the other work has been done.
The place is a reputable shop but I'm just thinking somebody (i.e. the guy who re-assembled it, who no longer works there... :gtfo:) didn't realise how hard these things are to bleed properly & the resulting hotspot has caused the problem I'm now loaded with. Either that or the head's only torqued to 58, we'll see when it comes out in the wash. Anyway you look at it I'm ahead though, the new 17" wheels & tyres fitted are probably worth as much as a Pajero with no MoT or tax, so the way I look at it is I've got a sickly-engined but otherwise mint Supra (I'll post some pics up when I've washed & waxed her) thrown in free for good measure!

P.S. the bubbles were pretty much clear (mainly because I've not been wasting antifreeze on testing the car, was going to refill with proper cooland had the HG turned out OK). Just the consistency of them, small tight packed bubbles about 1mm or less in diameter, reminded me of Aero bars. I'm guessing you don't have the privilege of light bubbly chocolate in the U.S. unless under some other guise...