Can't fix oil leak showing in rear oil pan area

[Jack O.]

Hi everyone,
I've made several posts in the past describing an oil leak I have showing in the area of the rear main seal/oil pan. I've replaced the rear main seal and the oil pan gasket more than once and am fairly convinced that it is neither of these two things. I'm getting ready to tackle it again this time ensuring that I have a good seal between the rear of the intake manifold and engine block. I was also told by someone on this message board that my problem could be an oil galley plug at the rear of the engine. Is this a possiblity someone could elaborate on? I assume this plug is accessible by removing the flywheel. I'm working on a '69 427.
Thanks again,
Jack

[Mike M.]

Re: Can't fix oil leak showing in rear oil pan are

there is a soft plug behind the flywheel that can leak. unlikely though. good luck.mike

[David B.]

Re: Can't fix oil leak showing in rear oil pan are

Jack,

Since you have already done the other leak areas, are you sure it's not coming from the front of the transmission case? The countershaft is a potential leakage spot and is a whole lot easier to fix.

Dave

[John M.]

Re: Can't fix oil leak showing in rear oil pan are

I used to have problems with oil leaks in my front engine dragster, once the engine is together remove the PCV rubber and duct tape it shut, put a air fitting in a oil cap (valve stem) and put 2 to 4 PSI in the engine you will find the leak..it should hold for 5 minutes or so.......Thanks John

[Joe L.]

Re: Can't fix oil leak showing in rear oil pan are

Jack-----

In addition to the rear main seal, rear pan seal, and rear intake manifold seal previously discussed, there are 4 possible leak sources from the rear of a big block. First, is the large soft plug at the rear of the cam. Second, are the 2 1/4" pipe plugs just above the cam soft plug. Third, is the pipe plug found on the lower, driver side of the block for the main oil gallery used on all Mark IV big blocks (except ZL-1). It's unusual for any of these to leak but it can happen, usually due to improper installation of the plugs. With the flywheel removed, it should be relatively easy to ascertain if any of these are leaking.

[Jim P.]

Re: Can't fix oil leak showing in rear oil pan are

My leak was from the rear cam plug. The plug is similar in size and shape to a "freeze plug." It is located on the rear of the block just above where you would normally find a leak for the rear main seal. Unfortunately, you have to remove the transmission to get to it.

[Jack O.]

NM: Thanks everyone for the help! *NM*

[Verle R.]

Re: NM: Thanks everyone for the help!

I assume you have checked the back of the intake manifold and the distributor. Those leaks normally flow down the side of the bell housing but could show up on the bottom.

Verle

[Clem Z.]

it could also be a leak between the block and the

rear main cap if it was not sealed correctly when the engine was assembled

[Dave Sly]

Re: Can't fix oil leak showing in rear oil pan are

Don't forget to check the oil pressure sending hole in the back/top of the block by the distributor. You might also have some oil coming from the draft tube connection in the rear block (not likely). Both of those may not leave much of a trace on the top of the block, however, they will leak down in the crack between the rear of the block and the bellhousing.

Dave

[Joe L.]

Re: Can't fix oil leak showing in rear oil pan are

Dave------

I think you're referring to a small block. I believe the engine involved here is a big block which doesn't have the oil pressure fitting in the same location as a small block. Also, big blocks didn't use the rear-mounted breather tube.

[Michael B.]

Re: Can't fix oil leak showing in rear oil pan are

Oil leaks flow down, so look up for the source. You might try the UV dye route if your having problems locating it. Check all the stuff high including distributor gasket, intake manifold and even the valve covers.

Although possible, I have never seen the rear oil galley or cam plugs develop a leak. Either they seal or they don't. They don't "wear out" causing a leak.

There are specific sealant instruction for the area between the block and rear main cap. Too much or not at all can cause leaks. Follow the instructions. I always push one end of the seal about 1/4" into the block and match the cap seal to it. This keeps the parting lines of the seal and cap from aligning and helps prevent leaks. Make sure the seal is lubricated before startup.

Also might mention that over tightening the oil pan can cause the areas around the bolt holes to pull in towards the block. If these areas are not flattened back before the new gasket is installed they won't allow the pan to seat fully on the new gasket.

[Michael B.]

Re: Can't fix oil leak showing in rear oil pan are

Oil leaks flow down, so look up for the source. You might try the UV dye route if your having problems locating it. Check all the stuff high including distributor gasket, intake manifold and even the valve covers.

Although possible, I have never seen the rear oil galley or cam plugs develop a leak. Either they seal or they don't. They don't "wear out" causing a leak.

There are specific sealant instruction for the area between the block and rear main cap. Too much or not at all can cause leaks. Follow the instructions. I always push one end of the seal about 1/4" into the block and match the cap seal to it. This keeps the parting lines of the seal and cap from aligning and helps prevent leaks. Make sure the seal is lubricated before startup.

Also might mention that over tightening the oil pan can cause the areas around the bolt holes to pull in towards the block. If these areas are not flattened back before the new gasket is installed they won't allow the pan to seat fully on the new gasket.