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[mikeh]

Now have cap with valve (thanks Razzo) and can produce constant coolant dribble at will.
Its not coming from the HBV and not leaking into the 'V'. The source seems to be back of engine on passenger side.
What's next to come off for a better look or any ideas where its coming from.
Thanks,
Mike.

[albitz]

Core plug is possible.Might be worth using a mirror and a torch to see if it helps locate the leak.

[mikeh]

Ok, thanks for the reply.
I'll try and make a mirror on a stick.

[RobG]

Now have cap with valve (thanks Razzo) and can produce constant coolant dribble at will.
Its not coming from the HBV and not leaking into the 'V'. The source seems to be back of engine on passenger side.What's next to come off for a better look or any ideas where its coming from.
Thanks,
Mike.

HG is favourite in that position

[mikeh]

Still not sure where leak is coming from but I have a bigger problem now - water in oil.
I knew I had an oil cooler problem as there were traces of oil in the header tank.
Could pressurising a cold cooling system (about 1 bar) force coolant into the engine oil?
Thanks, Mike.

[Andy H]

Still not sure where leak is coming from but I have a bigger problem now - water in oil.
I knew I had an oil cooler problem as there were traces of oil in the header tank.
Could pressurising a cold cooling system (about 1 bar) force coolant into the engine oil?
Thanks, Mike.

It shouldn't unless the heat exchanger is already weakened in some way.

The heat exchanger is made from multiple sheets of stainless steel welded together. It is very difficult to weld stainless steel to produce welds with the same characteristics as the components being welded. The chromium tends to migrate away from the weld to leave mild steel.

If you do have both rotten headgaskets and a failed oil cooler then it was probably caused by old antifreeze being left in the system long after its corrosion inhibiting properties had disappeared 

[Andy H]

Just re-read your post.

If your oil cooler is already faulty then, yes, 1 bar cold pressure test could force coolant into the oil

[mikeh]

That's encouraging. Thanks for the reply.

[MaxV6]

having suffered from a mystery leak like this 2 cars ago....   i've always kept an eye on such threads,  have to say, it would seem the most common cause is head gasket at rear passenger corner of engine...   

there are other causes, like transfer pipe o rings, and HBV, and so on, but the majority of cases seem to go though all those and then find it was the head gasket all along....   

sorry not to be cheerful with an instant fix....   

[dbug]

Just sorted this very issue today - 2.5 V6 Estate
Strip off plenum, inlet manifold and spacer plate - DO NOT drain cooling system before doing this.

With cap fitted to coolant reservoir, seal one of the cooling pipes removed from throttle body (pinching it closed will do), and blow down other to pressurise system. 

In my case leak was right hand side back of engine, traced to b*ggered seals on coolant bridge (use a good light + mirror + feel to identify leak source).  All sealing areas cleaned up and bridge refitted with new seals.

Also cleaned out breathers while I was at it - a good mornings work 

[amba]

Looks like this could be contagious

Driving home this morning was greated with lots of steam and coolant level warning

Pulled over and steam pouring from under plenum and water dripping down back n/side of engine.Mangaed to top up and got car home.Did logical thing first and replaced hbv with new spare had in stock for some time,but on replacing and starting engine again water still leaking so looks like will require day off tomorrow and pull it to pieces and pressure up the system.

Hope it is same as yours dbug as have a set of coolant washers ready for my exhaust manifold change so may bite the bullet and do the lot in 1 hit ...well assuming it is the coolant bridge or some other pipework around the back.

Please let it not be core plug or worse as have been almost clinical with coolant condition over the years of my ownership and would like to see another year or so from the car.

[andyc]

I had the very same problem last year and finally got it down to either the core plug in the back of the head behind the coil pack or the head gasket.

You gussed it, the head gasket. Left hand bank at the back. So that ended up being both head gaskets, bolts, stat, oil, oil filter, coolant, belt kit, water pump and aux belt plus a belt cover and a rad. (kindly donated by TB)

On top of that both manifold down pipe bolts snapped and had four snapped manifiold studs in the heads so a weekens work ended up being a weeks work

Cheers
Andy   

[amba]

I really didn,t want to be reading that andyc.

From the amount of steam and the fact that when water gets to temp it seems to be rising from the plenum and under the joint to the inlet manifold I am hopefull it will be the coolant bridge or pipe around there that has let go and is only doing it under pressure.Lots of coolant running down the back of engine but again only when pressurised.

Will get the pump on it in the morning after removing all the top end stuff and have a good look around as sure it will be evident when pumped up

I am thinking its pipe etc as it let go without any warning and up till then had no evidence of any coolant leaking....water pump/cambelt etc all done less than 10k ago by DLK so fingers crossed

[JamesV6CDX]

Should you not be able to do the work yourself, I am happy to do head gaskets for an excellent rate

[amba]

Thanks for offer James.

Will have a really good look in morning and get some pressure into the system which hopefully will show the culprit.

Perhaps you could drop me a pm with some indication of what costs are likely to be assuming "worst case senario" as I don,t live just around the corner either.