rear main seal or oil pan leak

[cameyer]

I have had a small oil leak on my 64 k10 and it has been getting progressively worse. My leak is coming from the back of the engine and is dripping off the bottom of the bell housing. There is also oil dripping from the 2 larger bots at the back of the oil pan. The oil is also all over the starter front drive shaft and oil filter. I have wiped all the oil off to try and trace the leak but i have no clue how to tell if it is the rear main or the oil pan. Can anyone help me figure out what is causing the leak?

[TopFuel1966]

My money is on the rear main seal. Remove the bellhousing (standard trans) or the torque converter/flexplate inspection cover (automatic). That should tell the story.

[T Smith]

Check the oil sending unit beside the distributor, very common to be leaking here and running down.

[Ronald29609]

The 350 I just rebuilt is leaking from the back of the motor. It hasn't been started yet. The crankshaft is .030 under on the mains. The seal came with a Felpro gasket kit.
Is there a special seal to use with an .030 under crankshaft?
There's a one piece neoprene pan gasket and a new pan so I don't think it's a pan leak.
Any help for a retired guy? I haven't done this kind of work in awhile.

[ACK]

The PCV on my 250ci wasn't hooked into the exhaust manifold when I purchased my truck, so it spewed oil from everywhere like a sieve. I hooked it up properly and replaced both the oil pan and valve cover gaskets, it's been tight as a drum ever since.

[cg285]

Originally Posted by Ronald29609

The 350 I just rebuilt is leaking from the back of the motor. It hasn't been started yet. The crankshaft is .030 under on the mains. The seal came with a Felpro gasket kit.
Is there a special seal to use with an .030 under crankshaft?
There's a one piece neoprene pan gasket and a new pan so I don't think it's a pan leak.
Any help for a retired guy? I haven't done this kind of work in awhile.

they don't usually turn that part of the crank

[brokenspoke]

Trace the oil up from the botton of the engine.....it could be rear main, oil pan gasket, intake manifold rear gasket, distrubuter gasket, valve cover gasket, pcv, oil sender....all the noted could wind up as you described

[brokenspoke]

BTW I would start at the top cost wise and work down.....valve cover cork gaskets start leaking slow and increase with age....I would change them out...cheap enough

[tincan1966]

Originally Posted by Ronald29609

The 350 I just rebuilt is leaking from the back of the motor. It hasn't been started yet. The crankshaft is .030 under on the mains. The seal came with a Felpro gasket kit.
Is there a special seal to use with an .030 under crankshaft?
There's a one piece neoprene pan gasket and a new pan so I don't think it's a pan leak.
Any help for a retired guy? I haven't done this kind of work in awhile.

You shouldn't have oil that deep in the pan that it would run out if not running.

[tincan1966]

Another possibly way to identify leaks would be to place a large piece of cardboard under the engine area. Start the truck and run it at about 1500 RPM for a few minutes. Let it idle and see if you have any notable steady drips. A rear main seal leaking will normally show as a steady drip while running.

Most of the time, a rear intake seal failure(on V8 engines), valve covers, and oil sender issues will drip after the engine is shut off, as it is residual oil running down the sides of the engine.

As mentioned before, make sure your PCV is working properly and that you have a crankcase vent, as well-either a filter type or a vented oil fill cap. The I-6 engine are notorious for oil leaking around the side covers after someone replaces the oil fill cap. Use of a non vented type on these engines creates pressure inside the crankcase and will push oil out of any small crevice it can find. The V8 will generally leak thru the front seal(behind harmonic balancer) in the case of a plugged PCV.

Just a little input from my experiences, hope it helps.