I have a '98 2-door Tahoe, and have some oil leaking from the motor. Due to a blown head gasket a little while back, I put in a brand new 5.7 crate motor about 5,000 miles ago. The new engine runs amazing and if it weren't for leaving evidence in every spot the truck has been parked in, you'd never know there was a problem. I have no check engine or low oil pressure lights. Both my inspection as well as the inspections from a few shops have shown that the oil is coming from somewhere in the upper rear against the firewall in the area of the oil sending unit. Underneath the truck, there's oil coming down both sides of the motor towards the back by the start of the bell housing and from up high. The amount of oil that drips to the ground when parked overnight is typically about the size of a silver dollar, so it's not horrible, but it adds up. Everything points to a slow, seeping leak. Before anyone asks, no, it's not contaminated. Just straight, pure oil. I've pulled, replaced, and re-sealed the threads on the oil sending unit and its elbow twice since that is the thing with the highest pressure back there, and that hasn't fixed it. The distributor gasket feels dry. I'm wondering if the "Form-a-gasket" crap that they use for the rear seal on the intake manifold is what's leaking. My next step is pulling the intake manifold to get a better looks and re-do the liquid gasket back there. Has anyone else run into this issue, and if so, what was the fix? Any recommendations? Thanks in advance!
'98 Tahoe Mystery Oil Leak
- Thread starter awalts
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east302
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Other than valve cover gaskets (which I imagine you would have seen leaking) the wall at the intake/block seems reasonable.
I guess try to dry it off the best you can and see what you can see with a mirror before yanking that thing off. With that much oil, it should be easy to spot if you can get an eye on it.
The RTV, technically, is supposed to sit for a certain period before getting wet. The bead isn’t supposed to be that large, maybe 1/4” wide (but I’d have to check the manual) and extends slightly under and onto the top of little tab of the intake gasket.
I guess try to dry it off the best you can and see what you can see with a mirror before yanking that thing off. With that much oil, it should be easy to spot if you can get an eye on it.
The RTV, technically, is supposed to sit for a certain period before getting wet. The bead isn’t supposed to be that large, maybe 1/4” wide (but I’d have to check the manual) and extends slightly under and onto the top of little tab of the intake gasket.
I agree with @east302. You should be able to dry the back of the intake off, from top or bottom, and then watch with a mirror. If it is coming down both sides, I would not think that both the valve gaskets are leaking at the same time unless, they may have both been sealed wrong as well. Have you contacted the engine supplier about this?
Yeah checking it with a mirror is a great idea. Definitely hard to get to though with the distributor sitting right there. Might need to remove the hood to get a clear line of sight. In terms of contacting the supplier, I have not. I don't suspect an issue with the motor itself. A lot of stuff had to be moved over from the old motor to the new one such as the oil sending unit, the distributor, and the intake manifold, so I think it is much much more likely I just messed something up when moving those things over. And those are my thoughts exactly on the valve covers. I'd need to have both valve gaskets leaking at the same time to get oil dripping down both sides, so that's not high on my list of probable causes. I suspect the RTV application at the rear of the intake manifold as the culprit. Feels a little wet in both of the upper corners of where the manifold meets the block, but I'll try and confirm with a mirror.
YukonGTmaster
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I would suspect the rear wall as well. When I did my lower intake gaskets the Youtubers recommended carrying that sealant bead up the wall and just under where the edge of the manifold gaskets squish down. Have you considered adding some dye, and checking with a UV light? I would also look at the warranty on that motor.
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Before you take it apart go to the parts store and buy a small bottle of die and put it in the oil. Get one of the cheap UV flashlights while you are there. Run it for a while to get the die circulated in the oil and then take a look. The die glows bright green with the UV light and you should be able to see where it is coming from. Other than the intake there is a 1/4" pipe plug that screws into a hole in the deck surface on the drivers side right near the top rear of the block. It is partially covered up by the cylinder head. If they didn't seal that plug correctly it might be leaking but that's pretty rare.
If it turns out to be the intake I have had the best luck with either "The right stuff" gasket maker or Permatex Ultra Black.
