Hard to find oil leak -GMC 2.8L - need help

A while back I posted a message asking for advice on replacing the valve cover gaskets on my 1985 GMC S15 (2.8L V6) which had been leaking oil. Well
the valve cover change (new Edlebrock covers, Carquest rubber gaskets) has been done and was sucessful, at least as far as I can tell. The problem now is that the VC gaskets apparently were not the only source of the oil leak. Apparently there is another leak on the top of the motor, on the back. This presents a problem for me since I cannot even see this part of the engine - its about 6" from the firewall and is covered with hoses, the distributor, etc. I did manage to look a little with a mirror and also get my hand back there and feel around and as far as I can tell there is a seam that appears to be the source of the oil. My question for the experts is what gasket could this be? I was thinking maybe the junction of the head and the block, could this be a possibility? All I've ever heard about head gasket leaks say that this means a coolant/oil exchange but I'm not showing any signs of this, just the oil leak. I've never seen the motor out of the vehicle so I don't know whats back there. Its not the distributor shaft, I can see that good. Could the manifold gasket failure or head gasket failure cause an oil leak back there? I've had a compression test done and compression is good on all cylinders, although not perfect. Please give me some advice as to where this leak could be, also if anyone has a close-up photo of the top back of this engine or one similar please email it to me so I can see what I'm looking for. The manual photo is not very helpful.
Thanks,
Casey snipped-for-privacy@hotmail.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I had a similar vehicle which required my replacing the intake manifold gaskets, the front and rear portion of which consists only of a bead of silicone gasket sealer. Common source of leaks. Mine leaked in the rear of the engine like yours.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Probably the intake manifold to block gasket is leaking.
--
Bruce
Westminster, Md
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well
now
leak.
This
engine -

appears
block,
say
oil
on
where
What is the evidence of a leak? Are you seeing oil underneath the vehicle? The 2.8 had a history of rear main seal problems. As old as yours is I'd almost hang my hat on that.
--

-Mike-
snipped-for-privacy@alltel.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mike,
The leak that I see (or have felt) is definately coming from the top rear of the motor, and runs down onto the front of the transmission, and onto the hot exhaust pipes below, where it sizzles and smokes like all get-out. It actually pools up in various pockets behind the manifold area. I can wipe it clean, but after a few minutes of running, it's pooled up again. This has caused a huge oil slick down the back of the motor and onto the transmission and oil pan. As for the rear seals, I cannot say for sure that they are not leaking also, as the entire back and underside of the motor seems to be covered in fairly fresh oil. Another thing that makes me suspect the manifold gasket is the fact that this engine overheated once years ago and I beleive the leak began shortly afterwards and has gotten gradually worse. How can I identify a rear seal problem? Would a rear seal leak come from the junction of the engine block to the transmission or is there another area to focus on?

vehicle?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

of
it
transmission
I'd go with the manifold gasket first as well in this case.
--

-Mike-
snipped-for-privacy@alltel.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
CNB wrote:

You may have an intake gasket leak, but it was/is very common for these engines to leak from the distributor shaft o-ring seal. The o-ring seal sits right above an oil gallery and is exposed to full line pressure. You might want to start by removing the distributor and checked the seal. If it hasn't been changed for a while, you will probably find something that is hard and cracks apart when you remove it. You can get the new updated seal from GM, it is a brown/tan color. This new one does not seem to deteriorate like the old seals did.
Ian
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The problem with the distributor shaft seal was also a problem on the newer 2.8s and 3.1s

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for the tip. I did see the place where the shaft goes in the block and all appeared dry in that area, but if and when they do the manifold gasket I'll get them to change out the distributor seal as well.
Casey

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Probably the area between the intake and the heads on the rear of the engine. The 2.8 uses part of the intake as part of the valve cover seat. That is the seam you found. You may as well plan on pulling the VCs, intake and resealing the top end. I hope the engine is in very good shape other than the leak. If not you may want to consider replacing it. The 3.4 will bolt in and give you some extra performance.
-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I just called a local machine shop where I was quoted $375 for a manifold gasket R&R job. That actually sounds a little low to me, since I have paid almost double that just to replace the VC gaskets (before doing it myself a second time). The engine still has good compression readings on all cylinders and as far as I know is in good shape. A brand new 3.4 would be nice, though.

News==----
Newsgroups
=----
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

a
Heh, if I'd paid $700+ for a valve cover gasket replacement, I certainly wouldn't admit it publicly. Sheesh........
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hairy,
I looked back at my receipt and it wasn't nearly as bad as I'd thought. The $700 included many other things including a compression check ($90) replacement of both front brake rotors ($70) and replacement of many vaccum hoses, not to mention the cost of all the parts.
The actual labor charged for the valve cover replacement was $240.
Now the proposed $375 for the manifold gasket replacement seems to fall right in line where it should.
Casey

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Casey,
the intake manifold is sealed with a bead of rtv sealant its probably old an leaking. I had a 85 blazer with same eng I can relate to little space issues. recommend you put new rtv back there to do this you must take out intake manifold whih may be more than you want to do. If its not leaking bad let it be and just check your oil every so often Bryan
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.