Oil leak and vacuum leaks -- what is the connection
 

I have read that solving a vacuum leak can stop an oil leak. Why? I thought the diesel engine doesn't develop vacuum and the vacuum system is totally separate from the engine. Why would a vacuum leak cause an oil leak?

Ok here is my guess................. and take it as that, strictly a guess.

The only connection I can see between those two issues in regards to a CTD is

In the Dodge application, vacuum is provided via the vac pump attached to the power steering pump. This pump vents to the inside of the crank case. remmeber that a vac pump is really a compressor too, if it sucks somewhere it has to blow somewhere right???

So if you have vacuum leak issues, the vac pump is going to constantly be drawing air in through the leak and exhausting in the cran case... This can cause added pressure inside the crank case and create leaks.

Also the vac pump seals are known to fail and create leaks. I have replaced mine in the '99 two years ago.

I hope my guess is somewhat helpful.

Wouldn't the crankcase breather take care of the added pressure?

take this with a load of salt.


You have the crankcase breather exhausting the crankcase, but you have a vacum pump exhausting into that. So now the vacum pump ( just for simplicity) adds 2 psi to the crankcase at over what it would have without it venting into the crankcase. Now on top of that you have the pressure being generated by the movement of the pistons. Can the crankcase vent exhaust all of that at the exact instant its created, maybe not so now you have kind of a constant pressure in the crankcase.

And if you have vacum leaks then its quite possible it may be adding even more pressure than just 2 psi. and even if its not adding actual psi its just the volume of air that it cant get rid of fast enough so it ends up generating psi because of what its putting in the crankcase and the movement of the pistons.

Does this make sense to people other than me. I kind of lost myself on it but dont know anyother way to explain it.

I understand what you are saying and this is what I thought myself. I bought my truck on 4/28. It had a bad leak and the cruise control didn't work. I found that the hard plastic line had broken clean off. I dug the broken part out of the rubber boot at the actuator and hooked up the line. My cruise now works and the oil leak seems to have become much better.

It is hard fro me to believe a 1/8" line could allow enough air into the engine through the vacuum pump to create pressure when there is a large vent tube to allow the air to pass through the engine.

BTW why does the pressure side of the vacuum pump vent to the engine and not just to the atmosphere?

Because, when the vacuum system is operating properly, the vac pump pumps very little air. Oil pressure feeds into the vacuum pump to lube the shaft and seal the pump vanes and drains into the timing case. Finding a way to make an exhaust without leaking oil would have been an engineering challenge so they decided to exhaust to the timing case through the same hole that oil drains through too (its a decent size hole, big enough for both air and oil). A common problem with our vacuum pump is the shaft seal at the rear of the vac pump. It is a single lip seal and wears a groove into the shaft, and after time it starts to leak. Oil goes out and air comes in, a double whammy.

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