Hi,

car has quite a high amount of blow by.... when the oil cover on the crankcase is closed there will inevitably be some oil seeping through it...... the oil pan has just been dropped and no mater how much silicon is used there is a occasional patch of oil on the floor..... and the oil pan is wet so I know it leaks from there,

I've told my dad that the pressure escaping through the cylinders caused by worn piston rings comes through and builds up so the heavy pressure contained there will cause it to leak eventually

Am I right or wrong?

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1975 240D W115 version 3 (Australian car )

You are correct. It is mixture of worn / tired rings and worn cylinder walls that allows the combustion gases to pass into the case.

If the engine has a history of neglect, some of teh rings could be stuck in the piston grooves as well.

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Increasing base pressure is a posibility. Make sure the crankcase ventalation system is in good condition.

Yes it does puff off smoke...... when I showed that to my dad he thinks every car has that and its normal
as for the leak he thinks he knows better than me there as well nothing much I can do about that

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1975 240D W115 version 3 (Australian car )

Some blow by is normal, and it is normal for well used engines to have more blow by. I don't know your particular engine but it has provisions to deal with the blow by, so it does not build pressure in the crankcase. Before I would worry about the serious stuff, I would make sure the crankcase vent system is not plugged up, as Barry has already pointed out.

could you elaborate a little on what you mean by "the rear main seal" would that explain why oil manages to seep through the oil pan?

I guess another reason to back up the fact that there must be some pressure building up in there is that the oil cap is extremely difficult to open after you've run some time and no matter how much you try to close it tight some oil will always end up around the cover


The ventilation system has no blocks.....

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1975 240D W115 version 3 (Australian car )

If there is oil showing along the oil pan sides it could be the front main seal. Remember oil always blow and travels to the rear when driving.
Check the front of the oil pan right below the front seal for oil there and wet behind the balance wheel.
Oil leaking from the rear oil seal only will blow back over the trani

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

If it is sticky piston rings it might be possible to free them up as in the thread below.

Marvel Mystery oil results sticky rings
Original thread also has + response
Compression Test...how low is low.....

Just the facts:
A compression test and a leak back test could tell you a lot and also give you an idea what needs to be fixed.

My Father had a gas car that would blow Oil past the Oil Pan Gasket if you left the Crankcase Breather on. If you drove without the Breather (not an overhead Cam so not so much Oil would come out) it was fine with the exception that the fumes would bring tears to your eyes.
In his case it was worn Valve/Valve Guides.

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84 300D, 82 Volvo 244Gl Diesel

Just a thought but could it be bad/worn valve seats?
how had is it to do the "pour some diesel on the valve and see if it goes through" thing?

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1975 240D W115 version 3 (Australian car )

Worn valves and valve stems are a very small blowby factor. Probably insignificant in even the worst cases.

Even when a valve leaks, the valve stems never experience any pressures remotely close to 'peak pressure' that the rings experience.


Using liquid is an effective means of testing for leaks.... but its hard to gauge the quantity with the head on block.

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