Burning Oil

[mashbury]

Hi all,

 

My 2001 115bhp Tdi PD is burning lots of oil..we are talking 450miles/litre. This is after I (otherwise successfully) took the head off and skimmed it to cure the overheating problem. Symptoms are, no blue smoke on start-up or when still cool, but after a few minutes, and increasingly as it gets warmer, get smoke. Much worse if I have been idling for a while, clouds of smoke, then dwindles to hardly noticeable as I drive along.

 

After much headscratching I have concluded that these symptons are consistent with faulty stem seals. I had replaced them all (plus guides) when the head came off, but maybe didn't fit them down on the guides properly.

 

Does anyone know how to, or have experience of, changing the stem seals with the head on? Has anyone experienced them coming away up the stem?

 

Is my diagnosis of valve stem seals correct?

 

Thanks

[howey]

Howdy

 

not sure if this itself would cause oil burning but if you have had the head off, i presume you removed the injectors, did you replace all the stretch bolts for camshaft and injectors? these bolts are once only use and i have heard the injectors can rattle in the head and ruin it...but like i said i aint sure if it would cause engine oil to be consumed? are you sure the turbos not drinking it?

 

(by the way i am a newby, do i need to post 3 times to be able to read the tech threads?)

 

cheers

 

Howey

[Amarok]

Hi,

if you had just replaced the seals and not the guides I would think yes BUT with the guides done at the same time to be totally honest I wouldn't have thought there was enough of a gap between the valve and the new guides to get a lot of oil down to the engine. Also if the engine stands overnight oil has a chance to drip drip drip down the valves so I would expect a cloud of smoke on first start up.

 

It is not a combination of oil leak and the breather blocked or blow by via the breather ??

 

Was the smoking bad after the rebuild or has it got progressively worse over time ?

Edited October 25, 2011 by Amarok

[sparky Paul]

Amarok's right, stem seal failure gives smoke on start up, which clears soon after.

 

Smoking when hot is more likely to due to oil passing up the bores, I would check for blow-by and consider a compression test.

[mashbury]

Thanks for the replies chaps.

 

1) Howey, I must admit I did not change the injector stretch bolts, but I'm pretty sure the injectors are seated well enough. What makes me think this (apart from getting over 45mpg) is that any oil that started to get down past the injector body would get to the fuel feed and return cross-drillings first..and there is no sign of dirty oil in the fuel return line.

 

I first thought it was the turbo, spent

[Amarok]

I managed once to change the oil seals with the head on (Ford Escort MK3 XR3i blast from the past) I managed to get some rope in through the spark plug hole and with the piston forcing the rope which in turn forced the valve shut I managed to do it BUT it was bl00dy awkward and compressing and uncompressing the springs was fun and if I dropped a collet well game over !! ;) Edited October 28, 2011 by Amarok

[sparky Paul]

I managed once to change the oil seals with the head on (Ford Escort MK3 XR3i blast from the past) I managed to get some rope in through the spark plug hole and with the piston forcing the rope which in turn forced the valve shut I managed to do it BUT it was bl00dy awkward and compressing and uncompressing the springs was fun and if I dropped a collet well game over !! ;)

 

Yes, I've done that too, it's fiddly but it does work. I ended up improvising a tool to compress the springs, fixing the fulcrum by an old head bolt in various positions. An assistant armed with one of those extendable magnetic pick up tools to retrieve the collets is also very handy... it's one of those jobs where you could do with three arms.

Edited October 29, 2011 by sparky Paul

[mashbury]

Well, I think I now have the answer. Seems a bit extreme, but may help others. This came from a VW-trained mechanic, who seems to know what he is talking about.

 

Basically I put a tight re-furbished head back onto an 200k mile old block, and this mismatch of `old' and `new' has caused the problem. The increased compression and more power, mainly from the head skimming but also from lapping in the valves, new guides etc has caused the rings to fail, noticeably the oil contol ones. The increased temperature caused by the original overheating problem would also have stressed them (it caused the head to warp after all). He has apparently seen this quite a bit. The rapid failure of the rings over a few thousand miles is typical, and is consistent with my oil consumption having increased steadily since the rebuild. I took the opportunity to really clean out the inlet tracts of all gunge etc. and the performance of the car is noticeably improved (even SWMBO commented on it!).

 

In other words my worn but serviceable rings have gone caused by fitting a well refurbished head.

 

Maybe this is one of the reasons VW say that the diesel head cannot (= should not) be skimmed?

 

I have endured a lot of angst and wasted a lot of time/ money chasing this one: I took the head off again, and replaced the turbo unnecessarily.

 

So lessons are:

1) Don't drive the car any distance once it has overheated, even if it after appears to be (nearly) normal

2) Don't skim the head unless you really have to (I did detect some distortion, but I may have got away with just new gasket).

3) Change the water pump with the cambelt

4) Check the electric overrun pump is working (mine had packed up more or less at the same time as the water pump)

5) Don't refurbish half an engine (old sack/ new wine)if the car is a high miler. I should have replaced the rings while the head was off(or worse had to check the pistons /bores)..which is hardly worth all the effor

 

One-off experience, but may help others.

 

PS Other thing he said was always use the pukka PD oil and change at recommended intervals...which we all do of course.

[sparky Paul]

Lots of manufacturers say you can't skim, but you have to play it by ear when it comes off. Oversize head gaskets are sometimes available if there is no room to manoeuvre.

 

You can usually get away with a light skim on most heads, and a little more with some, but if there is any evidence of distortion or surface pitting, you really have little choice. Putting a warped head back on is a waste of time and effort IMHO, unless you are offloading the vehicle sharpish. It's highly likely that the gasket will be pinched tight somewhere, and this will cause it to fail again, later on.