Thread: 240d blowby
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Old 06-27-2013, 01:59 PM
ah-kay ah-kay is online now
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Join Date: Mar 2009
Location: San Diego
Posts: 3,099
You need to measure the compression to see how bad or otherwise is the engine. Blow by normally is caused by low compression; worn cylinder or coking of the rings. Soaking with MMO is not going to cut it if the coking is bad, definitely not with worn cylinder. Thicker/heavy oil is a band-aid.

I have rehabilitated a OM603 engine with terrible blowby by removing the head and oil pan, pushed out the pistons from the bottom. Soaked the piston in solvent to remove all the carbon coking. Lightly honed the cylinders and then put the rings back in. I replaced all the oil rings as some were broken when I pushed the piston out. I reused the top rings. The compression was 50psi before and they were 260-300psi ( measured cold ) across all cylinders after the mini overhaul. It was all done with the engine in car. I have done 7K miles on the engine after the overhaul and it is running like a champ. No blow by to speak of. It is using a quart of oil per 1K mile. It is acceptable to me as the engine has 349K miles. I could not have done it without the help of this forum as I am not a heavy duty engine guy. It is a lot of work but it was a fun project for me. It does not beat playing golf but the satisfaction you get after fixing the engine is priceless. This is my experience and it works out well for me.

Good luck.
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

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