so i have a pretty bad oil leak. if the car sits still with the engine running no oil leaks out. if the car is driven then it starts to leak.
I have an old hot rod buddy that says if it only leaks from driving then it is the oil pan gasket. If it leaks from just an idle then it is the rear main. IS THIS SO?
it is coming from back of the engine out through the bell housing.

 

that's a pretty terrible generalization to make about an oil leak.

having just replaced my rear main seal, i am fairly certain that's what you are looking at. if the oil is really coming out from where you say it is, then you most likely have a leak at the rear main.

 

Sounds like it. Check valve cover gaskets too, if it fell apart at the rear of the cover it could do that as well.

 

My car does the exact same thing since I changed the pan and gasket. It is the rear of the oil pan gasket leaking on mine and probably on yours.

 

How is an oil pan gasket any more of a terrible generalization than a rear main seal?
They are both probable solutions to the problem, and i would even venture to say an oil pan gasket is more likely than the rear main seal.

 

nice misunderstanding. his friend said that driving leaks are caused by oil pans and idling leaks are caused by rear seals. that is over-simplifying things.

and if his rear main seal is stock, it is MUCH more likely that is the culprit than the pan gasket. if he already has a newer style rubber rear main seal, then yes of course, i would bet its oil pan gasket too.

 

actually its fairly logical. the rear main leak happens as the crank is spinning, if it's not leaking at idle than its likely not the main. Leaking while your driving is probably a result of the oil being pushed to the back of the block due to momentum, but could be the pan or valve covers. So, this generalization is not that far off base.

 

It's probably the oil pan but just for giggles, don't rule out any leaks from the top finding their way to the bottom. Different engines have different issues. Leaks can come from oil senders, valve covers, intakes and more.

Be sure to check the crankcase vents. If the crankcase can't breathe, it will cause leaks. Blowby WILL find its way out.

 

Hmm,
His friend said driving ONLY and idling ONLY. that's different than what it appears you have interpreted.

Tell me how a rear seal could leak driving only?

 

the crank doesn't spin at idle?! well shoot, i just learned something new today