Why does oil only leak when driving?

[AnarchyX]

Ok so I've got an '02 GMC Envoy that loses about a quart every 1,000 miles. Fortunately it's being lost through leaky gaskets and not because of engine related issues. She hasn't lost a step in regards to power/acceleration, mileage, etc., and she's been like this for about 40,000 miles out of 194,000 so far.

That being said, I'm just wondering why it doesn't leak when parked. I don't mind not having the puddle of oil in the driveway of course, just wanting to know for my own sake really.

Thanks

 

[Lead Shoes]

Depends on what seals are leaking, if they only touch oil when the car is on, that would be the reason.

Have you ever looked into exactly what seals are leaking?

 

[sasilverbullet]

There are quite a few places on engines where a leak may only show up while the engine is running - valve cover gaskets, main seals, etc.

 

[Hokiefyd]

Oil generally doesn't leak when the engine is off because oil must be contact with the leaky gasket to leak through it. This happens during operation because oil is splashed about inside the engine. When parked, it's sitting in the sump, presumably below the level of the gasket.

This may not apply to a cylinder head cover gasket, especially on a V-type engine, where the bottom rail may always be bathed in oil. A leak here can and will drip at all times, and not only when the engine is running.

 

[default]

All the oil is pooled in metal pockets in the head, the lifters, the oil pan, and the oil filter when it isn't running. When you start the engine, oil starts flowing, draining and spraying everywhere, and in the case of the front and rear main, applying pressure to the seals.

 

[AnarchyX]

I see no leaks on top of engine, and my mechanic says there's no leak on rear engine seal. He did mention though that the valve cover (front of the engine) was leaking a bit.

If that is the only place it's leaking could that be the reason why?

 

[Lead Shoes]

It would be a VERY significant valve cover leak to make 1qt per 1000 miles... you likely would have caught fire by now with that much oil going onto the manifold while running.

 

[[email protected]]

I had a 2002 Envoy too. Have fun replacing the valve cover gasket!!! The whole intake manifold has to come off (MAJOR PITA). Mine started leaking around 125000 miles and I didnt replace the valve cover gasket til around 150000 miles. Would go through 2.5 quarts or so between 7500 OCI's. Synpower isnt cheap!! was more economical to just fix the leaks and keep adding expensive synthetic oil in the sump

 

[cchase]

Originally Posted By: Brenden
It would be a VERY significant valve cover leak to make 1qt per 1000 miles... you likely would have caught fire by now with that much oil going onto the manifold while running.


I had to add a quart of oil every 250 miles to someone elses car once due to a cracked valve cover. The car would not drip but boy was it spraying it around while driving.

 

[mrflex65]

I know this is a long shot,but perhaps it might be the oil pressure sending unit? Had that happen to a couple of my cars, but that was years ago....

 

[Trav]

+1 Definitely worth looking at.

 

[SwampSurvivor]

Originally Posted By: Brenden
It would be a VERY significant valve cover leak to make 1qt per 1000 miles... you likely would have caught fire by now with that much oil going onto the manifold while running.


Friend of mine has a Santa Fe 2.4 with a very leaky valve cover gasket.

You can see it running out while it's running. Thing always smells like burning oil and goes through a quart in about 750 miles from leaking.

No fires (yet)

 

[TFB1]

Originally Posted By: Brenden
It would be a VERY significant valve cover leak to make 1qt per 1000 miles... you likely would have caught fire by now with that much oil going onto the manifold while running.


Agreed, if it were leaking enough to use a quart in 1K mi, you'd have oil drips hanging off the bottom of the engine leaving some spots... If it were getting on the exhaust their'd be some smell and probably smoke...