Engine leak - Part II

[67Fleet]

Well, seems my oil leak is getting worse. I still haven't been able to isolate exactly where it is coming from, but it is somewhere on the back of the motor on the driver side between the valve cover and just above the oil filter housing. (that's why so hard to find the exact spot, it's so darn hard to get my eyes back there to see anything!). Last night I drove the truck to Old Town for the cruise and got back and there was oil all over my exhaust pipe and this morning when I checked underneath, there was a small pool the size of a shop towel on my garage floor.
Today I looked at everything I could, cleaned up a lot of crud underneath while I had it jacked up, changed the oil/filter, and did a compression test on all the cylinders to see what I was dealing with.

The good: No antifreeze in my oil, it didn't appear to be contaminated at all.
The bad: The leak seems to be getting progressively worse and I don't know the root of the problem. May have to pull the motor or have a leakdown test done.

Here's the cylinder compression test results (without firing orders, I'll try and map it out how I did it)
back of motor
pass side driver side
182psi 183psi
188psi 180psi
190psi 169psi
190psi 187psi
front of motor


The one cylinder 2nd back from front on driver side is a concern since it was so different. Any ideas from all this info on what my leak problem could be? Since there is only 1 cylinder drastically different, and no antifreeze in my oil I think I can rule a blown head gasket out. Something's probably cracked and I'm screwed. That's my luck.

[powell72]

That compression seems good to me, your always going to get a range in the reading when your dealing with hydraulic lifters. I would spray the back down with some brake clean and then let the truck run and stick a small mirror back there so you can get an idea where it is. I wouldn't get too bummed yet, it could still be something fairly easy.

[Billla]

Ok, let's think about this for a minute - you've got a leak but it's running fine otherwise? I wouldn't be worrying too much about engine condition...just on finding the leak. If something was cracked you would be dealing with other more significant issues than an oil leak IMHO.

Can you get a light and mirror in to look at the rear of the block above the bellhousing? Should be able to get in there lying across the engine to have a look. Two common leak sources there are a) the distributor, especially if it's got an adjustable collar and b) the oil pressure sender (electric) or tap (mechanical).

If it's clean above the bellhousing...the only things I can think of are the rear cam plug or the rear main seal. These are both not good, but I would expect you could get a pretty good look by removing the lower bellhousing shield and getting a light up in there.

[Hart_Rod]

Napa sells a chemical that you put in the oil that can only be seen with an ultraviolet let. Put it in the oil, run the engine for a little while, turn lights out and look for leak.

[mblackburnjr]

Oil pressure sender would be a good guess. My buddy replaced an intake once and cracked the sender rt at the bottom near the block. His symptoms were alot like yours. Hope ya find it!

[Longhorn Man]

Run your finger around the head under the valve cover... if your finger comes back clean, then do the same on the top of the block right behind the intake manifold.
Those seem to be the top 2 places in my experiance.

[clay68c10]

A telescoping mirror and drop light are your friends! Does the intake manifold have the rubber end seals? I don't think you would get a big leak but it's something to check as those are prone to squeezing out and leaking.

[Billla]

Originally Posted by clay68c10

A telescoping mirror and drop light are your friends! Does the intake manifold have the rubber end seals? I don't think you would get a big leak but it's something to check as those are prone to squeezing out and leaking.

I never use the rubber seals, so I forgot all about this.

[Longhorn Man]

oh yeah, the intake can create a MASIVE leak. We're talking spraying the firewall type leak.

[dwaite72lnghrn]

Has anything been done to the engine lately? This could point to something. Valve covers, rear intake, oil sender and lastly check the PCV valve is working. If it is stuck closed pressure will build in the engine and cause big oil leaks. If it is stuck open it will suck oil into the carb.

[ed455]

There are at least THREE pressurized oil ports plus the intake gasket. All on the drivers side. There's the one in the back intake sealing surface and one down on the horizontal surface just above the tranny mounting surface and one on the vertical surface just below it and usually one down by the oil filter. As previously stated by others, rear intake gasket seal is a common leak. Just fixed that one on my neighbors Chevelle Saturday. If your sending unit is in one of those ports, it is a common leak as well.

Your compression is just fine and oil leakage is almost never a "engine problem." You should be able to quit worrying about a bad motor and concentrate on finding the leak. If it's an oily mess already (as you describe), you have GOT to clean it up to find the leak.

[ed455]

Oh, and if it's intake leaking, DON'T use the stupid rubber seals that come with the intake gasket. Big bead of black RTV is what I use and never have leaks.

[Steelawork'n]

What year is the engine? Did you switch from the canaster type oil filter to the spin-on? If you did, there is still a seal you have to replace behind the adapter every time you change your oil. If you don't, eventually it will leak really bad.

[67Fleet]

Originally Posted by Steelawork'n

What year is the engine? Did you switch from the canaster type oil filter to the spin-on? If you did, there is still a seal you have to replace behind the adapter every time you change your oil. If you don't, eventually it will leak really bad.

Not sure what year the motor is. I do know it has late model Vortec heads. It does have a spin-on filter.

I am pretty sure it is coming from the top of the bellhousing on the driver side, right in that top corner since I thoroughly cleaned that and then took it for a test drive. Came back and ran my finger around that area and I got oil. Is that the rear main seal? If so, what all is involed in fixing that? I know just from people talking about it that it is a complete PITA.

[ed455]

Originally Posted by 67Fleet

Not sure what year the motor is. I do know it has late model Vortec heads. It does have a spin-on filter.

I am pretty sure it is coming from the top of the bellhousing on the driver side, right in that top corner since I thoroughly cleaned that and then took it for a test drive. Came back and ran my finger around that area and I got oil. Is that the rear main seal? If so, what all is involed in fixing that? I know just from people talking about it that it is a complete PITA.

If it's coming from the TOP of the bellhousing area it's NOT the rear MAIN seal, but more likely the rear MANIFOLD seal. What's involved in fixing that, it removing the intake manifold, cleaning the old gaskets and seals off the block and heads and installing new gaskets and RTV front and rear of the intake. Once the intake is off, you be able to see the other pressurized oil ports and maybe your oild pressure sending unit, depending on where it's installed.

Ed


.

[shifty]

go get some of that UV-reactive stuff to add to your fluids. just put some in your oil, then put a blacklight on it. it will show where your leak is coming from. don't forget to keep a mirror handy.

[Steelawork'n]

I agree with the intake seal. I'm also wondering if you have a small head gasket leak because of the 169 psi on the driver's side. If it was me, I'd do the right side HG while I have the intake off.