940 smoking/burning oil

[Laird Scooby]

Originally Posted by griston64

Hi Dave

Service book for UK suggests 10w 40 semi which is what I've always used.And also just bought to do a change next week. Is 15w 40 better for the engine ? Or an older engine ?

Cheers, Mark

Spot on Mark! In an older engine going slightly thicker (even up to 20W50) can help to reduce oil burning. Go back to the 140 series of the early 70s and 20W50 was the recommended oil.
Manufacturing tolerances have tightend since and the OHV B20 sprouted an OHC arrangement, fuel injection and turbos so the oil was made more suitable. In some climates, even with all that, 20W50 is still the recommended oil.

Most of the time, red blocks don't seem to liek fully-synth as it was more or less witchcraft when the redblocks were first designed. Even in my Rover that's a much more modern design than the red block, fully synth isn't recommended and if someone uses it, fuel economy, power and oil consumption suffer.

My line of thought on this one is the oil the OP used was too thin and has caused him problems, hence suggesting 15W40 to help get things back on an even keel. If it's still burning oil after my suggestions, he's going to need to start taking things apart.

[aardvarkash10]

lots of high detergent cleaning products have been used, so I figure that a lot of carbon and build-up has been removed and has exposed old, tired seals.

On over-run, the oil is only likely to be coming from one of two locations - valve stem seals, or rings. Stem seals are a relatively easy problem to solve, rings less so.

[Laird Scooby]

Originally Posted by Jelle9990

Here is the plugs! Don’t know why it doesn’t wanna upload the picture from cylinder 3, but I looks like the others soo I guess it doesn’t matter too much

Those plugs look fairly normal, no signs of oil fouling but the gaps look a bit large like about 1.1-1.2mm. Could be camera angle i suppose but try setting them back to 0.7mm as they should be. If nothing else it should run smoother.

Originally Posted by aardvarkash10

lots of high detergent cleaning products have been used, so I figure that a lot of carbon and build-up has been removed and has exposed old, tired seals.

On over-run, the oil is only likely to be coming from one of two locations - valve stem seals, or rings. Stem seals are a relatively easy problem to solve, rings less so.

That all came into my thinking on the oil i suggested as well Ash.

Thing is, if the smoke is white then it's burning oil after the combustion chamber, if it was blue it would be burning oil and petrol together in the combustion chamber, hence my thoughts about the turbo oil seals. I suspect because of the excessive pressure in the crankcase caused by the blocked breahters, the oil pressure has risen and blown past the turbo oil seals and into the intercooler so is pulled through on maximum vacuum i.e. the over-run when there will be no petrol anyway due to the fuel cut-off.

I coulod be wrong but it's a theory worth exploring and certainly a logical one.

[aardvarkash10]

missed the white smoke bit. Still too early here and a french toast/bacon/cream/peaches breakfast had me focussed!

[Laird Scooby]

Originally Posted by aardvarkash10

missed the white smoke bit. Still too early here and a french toast/bacon/cream/peaches breakfast had me focussed!

I hope the peaches and cream weren't on the same plate as the French Toast and bacon?

[aardvarkash10]

Originally Posted by Laird Scooby

I hope the peaches and cream weren't on the same plate as the French Toast and bacon?

Of course they were! Very continental/US approach to breakfast.

Home-made pork pie for lunch too! Gotta love being locked down.

[Jelle9990]

Soooo first move is to clean intercooler(pipes also?) and check the PCV again? If that doesnt work out, 15w40 semi synthetic?

No one wonders why there isn’t coming ANYTHING in my catch can?

[griston64]

Originally Posted by Jelle9990

Soooo first move is to clean intercooler(pipes also?) and check the PCV again? If that doesnt work out, 15w40 semi synthetic?

No one wonders why there isn’t coming ANYTHING in my catch can?

I wouldn't be to worried about the pcv tbh. My breaker on 220k ran as sweet as anything with no smoke and the pcv pipe was pretty much blocked solid.

I would check pipes that go into your intercooler first. If they are really oily ( not just a normal smearing ) it would suggest the turbo. If not I would say it's valve seals.

[Laird Scooby]

Originally Posted by Jelle9990

Soooo first move is to clean intercooler(pipes also?) and check the PCV again? If that doesnt work out, 15w40 semi synthetic?

No one wonders why there isn’t coming ANYTHING in my catch can?

What Mark said in the post above explains why there's little or nothing in the catch can - there shouldn't be. I was suggesting recleaning the PCV as a precaution but my big suspicion is the intercooler and pipepwork to/from it.

So far most things point to the turbo seals, perhaps they were compromised as i outlined further up because the crankcase pressure forced the oil into a higher than normal pressure and blew past them, causing the original smoking.

I'd still suggest 15W40 semi-synth in place of the fully synth as generally speaking, red blocks don't seem to like fully synth. Also given the heavy cleaning you've done with engine flush etc, as Ash pointed out, it may have taken some of the carbon away that was helping to seal things on an older engine.

[griston64]

See notes re oil

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