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OM 642 blow by

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Old Apr 12, 2024 | 11:16 PM
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wannawagon
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
OM 642 blow by
2008 GL320 with huge blowby. Only got about 180kkm on it. In Australia so no DPF

I have had a few of the om642 motors (normally higher km) and never had this issue

I have put a catchcan on it (years ago) and can feel pressure in the hoses (from pcv) but the oil filler cap has way more pressure.

I have to travel a few hundred km to get home so have routed the catch can vent out the right wheel arch so as to limit oil going into turbo (and intake) and have bought a heap of oil

No visible smoke out exhaust

I remember looking at a gl320 years ago at auction with similar high crankcase pressure but i just decided to pass on it so never knew diagnosis

any thoughts appreciated
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Old Apr 13, 2024 | 10:38 AM
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1922 Ford Model T / no OBD
How big is it?
Will napkin stay on fill hole while engine idling?
How about cardboard?
My OM642 has 216k miles and blowby is minimal.
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Old Apr 14, 2024 | 01:07 AM
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Originally Posted by kajtek1
How big is it?
Will napkin stay on fill hole while engine idling?
How about cardboard?
My OM642 has 216k miles and blowby is minimal.
sorry about delay. The blowby is pretty bad. When I remove filler cap I hear a pop and oil is pushed up the dipstick tube. If I put a rag over it I think it will just create more mess

I am going to try and vent from pcv straight to atmosphere and see if reduces back pressure. I remember the catch can I put on has a screen which may have been blocked

pretty sure the cause of the obvious leak was the dipstick moving out a little. Like if you pull it out a mm oil pours out.
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Old Apr 14, 2024 | 10:36 PM
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From: New Hampsha
'17 GLS450, '14 GLK250, Grandpa's Roadster
Originally Posted by wannawagon
When I remove filler cap I hear a pop and oil is pushed up the dipstick tube.
I'm confused. Wouldn't removing the fill cap relieve any pressure in the crankcase? Seems with the cap on the dip stick would be pushed out, along with the oil. Am I missing something?
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Old Apr 14, 2024 | 10:42 PM
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Originally Posted by John CC
I'm confused. Wouldn't removing the fill cap relieve any pressure in the crankcase? Seems with the cap on the dip stick would be pushed out, along with the oil. Am I missing something?
should have been a comma in there. If cap is on the oil comes out the dipstick tube if not fully in housing.
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Old Apr 15, 2024 | 12:26 AM
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1922 Ford Model T / no OBD
That's pretty obvious signs of something wrong with pistons, or rings.
You can run smoothest test, to pinpoint the cylinder and take snake camera to look inside.
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Old Apr 15, 2024 | 01:47 AM
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Originally Posted by kajtek1
That's pretty obvious signs of something wrong with pistons, or rings.
You can run smoothest test, to pinpoint the cylinder and take snake camera to look inside.
not sure on “Smoothest” test. Is that a compression test?

The lack of blue smoke out the exhaust is a bit baffling to me.

thought if I had scored bores I would have oil smoke.

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Old Apr 15, 2024 | 02:11 AM
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Originally Posted by kajtek1
That's pretty obvious signs of something wrong with pistons, or rings.
You can run smoothest test, to pinpoint the cylinder and take snake camera to look inside.
not sure on “Smoothest” test. Is that a compression test?

The lack of blue smoke out the exhaust is a bit baffling to me.

thought if I had scored bores I would have oil smoke.


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Old Apr 17, 2024 | 11:20 PM
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From: V E G A S
1922 Ford Model T / no OBD
Good scanner will make the test for you.
there are 2 of them
1 simulated compression test
2 injector test
You need #1 for sure.
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Old Apr 17, 2024 | 11:27 PM
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Originally Posted by kajtek1
Good scanner will make the test for you.
there are 2 of them
1 simulated compression test
2 injector test
You need #1 for sure.

Will chase up a better scanner - wow didn't think a scan could do compression - many thanks
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Old Apr 18, 2024 | 04:34 PM
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From: New Hampsha
'17 GLS450, '14 GLK250, Grandpa's Roadster
Originally Posted by wannawagon
wow didn't think a scan could do compression
It doesn't actually measure compression pressure. It measures angular acceleration and deceleration of the crankshaft while cranking with the starter and deduces compression from that.
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