Hiya
If I list the symptoms - can somebody check my logic? Also is there a common location where the head gasket fails on the mk3 GTI's? Engine in question is the 8v AGG - about 80k miles.
1) Oil residue in the air box - despite cleaning
2) Oil being blown out of the oil filler cap
3) "Blowing" noise from the airbox when there is any load on the engine. Exhaust has been checked twice and is 100% ok.
4) Gurgling / running fluids sound when the oil cap is removed when the engine is running. By this I don't mean the puff-puff-puff sounds of the compression cycle. Sounds like air is blowing through fluid (oil!?).
5) Possibly a very slight water loss - but this could be a minor radiator leak - so not so worried about this one
6) Lumpy idle
7) Its very hard to drive smoothly when hot and in traffic - i.e. start stop - low RPM. Never sure whether it'll shoot off or stall when I pull off.
8) Cylinder compression was 165,165,145,145 (PSI)
9) No mayonase. No oil in the water. No overheating.
Have checked the PCV breathers - all clear. My hypothosis is that the gasket is starting to give between 3 & 4 and into the oil channels? Is this a common failure?
Local garage is not convinced - mainly I think due to (9).
Cheers much!
James
Edited by Javalin on 23/11/2009 at 20:45
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Doesn't sound like head gasket at all, the symptoms point to either a blocked crankcase breather system or engine wear.
A leaking head gasket will give pressure in the cooling system sufficient to blow the water out of the overflow/filler cap and or oil in the water and water in the oil.
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Hi PeterD
Thanks for the response. Surely the HG can fail into the oil channels too?
The PCV pipes are all clear.
This is a very recent thing - so probably not engine wear?
James
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i would want 170 a pot so the head or rings might need an overhaul
take car to an mot station and ask if they can do an emissions test or better still a sniff test of your overflow bottle
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Hiya
(sorry meant peterN not D!! Oops)
OK - its in the garage ATM - so I'll enquire when I go get tomorrow.
>i would want 170 a pot
??
> the head or rings might need an overhaul
oh. Expensive I guess.
James
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It's a gti it will have been driven hard and they take it im sure it's rings just passing 80k on a 97 plate are you sure that is correct?
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It is indeed possible for the head gasket to leak into the oilways, but I have never heard of it happening without water leaking in as well. The area of the head gasket with water flowing through it is about 100 times that of oil - possible but unusual, What you are getting though is combustion gasses into the sump, broken rings could well be the problem.
Edited by Peter.N. on 23/11/2009 at 23:37
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Just spoken to the garage who've been looking at it. They recon their machine got 180psi +/- 10% across the 4 cylinders. Something is not right with this story - if there is good compression then where is the blowing air comming from?
Any thoughts welcome. Tempted to get second opinion at VW?
James
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Could it be the camshaft has moved a tooth or two wrt the crank, so that valves are open at the wrong time? Might account for the intake noise at least...
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hiya,
good thought. I've checked recently and it was spot on (cam & crank and flywheel). I've not checked since - but a good idea.
Wouldn't that show as low(er) compression though?
ta
James
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Wouldn't that show as low(er) compression though?
Peak pressure would probably still be the similar i'd guess?? But thinking more, it wouldn't come close to accounting for all the oil/crankcase issues. An 80k engine shouldn't show serious head or bore wear... The failed piston ring sounds favourite, but it's odd that it should have gone back up to full pressure again. Be interesting to hear whether the pro's have heard of rings temporarily mending themselves in this way...
Edited by dimdip on 24/11/2009 at 12:18
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This all sounds a trifle odd, with compression like that at cranking speed you wouldn't expect a lot of blow by, does the brake vacuum pump discharge its output in the crankcase breather system?
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>This all sounds a trifle odd
indeed.
>with compression like that at cranking speed you wouldn't expect a lot of blow by,
no.
>the brake vacuum pump discharge its output in the crankcase breather system?
Petrol's don't have a vacum pump do they? Does the ABS system have a pump? Brake vacum connected to intake manifold as far as I can see. Brakes work extremely well.
Thanks chaps,
James
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>Be interesting to hear whether the pro's have heard of rings temporarily mending themselves in this way...
but here's a thought.... If the car wasn't used for a week or more (which it hasn't been as I thought HG was failing) - would some oil seep into the cylinders and temporarily seal the rings??? It seems better when not used for a bit on reflection... Will have to drive it more before taking it anywhere else to be examined...
James
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Breather pipe from sump splits & the breather chambers do clog up inside causing oil in the air box & lumpy idle. Ensure breather chambers are spotless.
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ok. Not seen a breather from the sump - but will check tonight.
Have booked it into VW tomorrow for a second opinion. Will mention breathers and such.
Cheers all!! :-)
James
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i suspect breather problems, piston ring problems are not common but they can fail. The easy check for a garage is a cylinder leakage test. Compressed air is fed in via the plug hole whikst the cylinder is on the firing stroke & the engine locked by putting in 5 th gear. Excessive piston blow by will be detected in the breathers & the measured air loss. If the head gasket has blown across an oil return gallery you will also get excessive air in the breather system. To distingquish between the two you then put oil in the suspect cylinder, if the leakage is reduced the rings are sus but if no change the rings ok.
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Sorry about the vacuum pump goof - I've run diesels for so long I have forgotton what a petrol engine is like.
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