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Old 21-09-2010   #1
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Losing oil through crankcase breather.

Hello all.

I bought a 20 year old motorhome which was losing oil through the breather at the front of the engine when travelling at 60mph+. The previous owner had disconnected the breather pipe from the air filter and instead, vented it off into a little home made catch tank. I presumed the engine was just a bit 'worn' and had the motor factory re-conditioned.

Now, the re-cond engine is now in, it runs fine but still has exactly the same problem. I have done 5,000 miles on the new engine and during this time have put about 8L of oil in her. I have checked the oil separator and the gauze was clean.

What can be the cause of this oil loss? Could something else be causing excess crankcase pressure? I would expect to lose a tiny amount of oil in the form of vapour through the breather but in my case it is excessive. The engine doesn't smoke (apart from a few seconds from cold) and otherwise runs well.

The engine is a 1990 2428cc turbo diesel in a 4000kg Hymer.

Any ideas appreciated..
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Old 21-09-2010   #2
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Re: Losing oil through crankcase breather.

Have you checked each cylinders pressure?
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Old 21-09-2010   #3
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Re: Losing oil through crankcase breather.

I had ruled out loss in compression because the same problem had existed before the engine rebuild as well. Now that you mention it though, I will book it in for a compression check just to be sure.
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Old 21-09-2010   #4
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Re: Losing oil through crankcase breather.

What height is your can installed at if too low it will spew oil anyway.

Exhaust blockage could feasibly cause it.
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Old 22-09-2010   #5
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Re: Losing oil through crankcase breather.

I have a length of pipe coming from the small oil separator at the front of the block. This pipe loops up higher than the height of the cylinder head and then trails back down to about the level of the oil filter.

Corkman, if you say exhaust blockage could cause this then maybe something wrong with turbo? Is there a way of testing exhaust back pressure?
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Old 22-09-2010   #6
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Re: Losing oil through crankcase breather.

Quote Originally Posted by Kernow man View Post
I have a length of pipe coming from the small oil separator at the front of the block. This pipe loops up higher than the height of the cylinder head and then trails back down to about the level of the oil filter.

Corkman, if you say exhaust blockage could cause this then maybe something wrong with turbo? Is there a way of testing exhaust back pressure?
First question:
You say you put 8l of oil in 5k miles but how much oil have you removed from the catch can? Has the catch can been filling up?

Second question:
What diameter is the pipe to the catch can, could there be a siphonic action going on?

In relation to a possible exhaust blockage, it could be the turbo yes but much more lightly that the exhaust is rotten and the wadding and soot it blocking it.
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Old 22-09-2010   #7
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Re: Losing oil through crankcase breather.

Yes, the catch tank fills up at the rate I put new oil into the engine. I don't put the caught oil back in to the engine as the home made system is open to the elements. I am 100% sure all my oil loss is through that breather.

The breather pipe diameter is the standard size which fits on to the oil separator, its about 30mm give or take.... I can't see how there could be some siphonic action going on there. I think oil is coming out in very small amounts until the engine is under strain, overtaking, hills etc.

I am curious about your blocked exhaust idea. Have you known such a thing? I mean, for a motor to start up easily and run ok but to have an exhaust blockage? I suppose I should get a garage to investigate all these things. It is good though to get a list together of things to trouble shoot before I take it in.
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Old 23-09-2010   #8
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Re: Losing oil through crankcase breather.

I was thinking by logical elimination if your sure the engine has been rebuilt properly and tested then the things that are the same are the exhaust , manifolds, turbo. As the revs increase the exhaust valve stays open for a shorter and shorter period of time also as your foot goes to the floor more gases have to exit the exhaust in that time. If the exhaust velocity is reduced the gases don't completely exit and the cylinder remains pressurised.
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Old 23-09-2010   #9
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Re: Losing oil through crankcase breather.

I am going to get all these things checked out. Compression test, Exhaust, manifolds and turbo. Then I am going to report back here! I don't want folk racking their brains too much if I have missed the obvious. At least I have a few things now to eliminate!
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