91 ZR1 - Latest Issue

[TealZR1]

See Pic - just developed an oil leak coming from the read end of the oil pan - leaves a decent size puddle of oil after it's done. Looking closely appears to be a pin hole developed? But possibly a bad gasket. See pic and let me know of any suggestions to look for. 62K miles. Thanks

[A26B]

Pan bolts tend to loosen over time. Tighten all M8 pan bolts to 23ft-lbs. The remaining 3 M6 bolts in the very front are hard to get to without removing the K-members. Proper torque for them is 89 in-lbs.

Try tightening all of the M8 pan bolts first to see if that helps. If you still see any leaks at the front of the pan, then pursue the M6 bolt tightening process.

If leaks persist, it will require a new pan gasket.

[Paul Workman]

I feel your pain! One other source USED TO BE seepage from the breather box and hoses, under the plenum. New gaskets and blue Loctite and hoses eliminated that. No more oil collecting in the valley after that, so nothing going down the drain tube...

That leaves the rear main seal and the pan gasket, I guess. :censored:

[TealZR1]

Thanks Paul and Jerry. And Jerry, I understand you're the gasket king which I may be a calling.
The car literally went one day with no drips of oil to last week a good size puddle larger than a hand every time I take it out for a drive. The leak is in the back of the oil pan. Could this be an issue with a bad gasket coming out of nowhere and going bad quickly? Thanks again

[QB93Z]

Another possible source of that much oil is the rear crankshaft seal. Jerry has them.

Jim

[32valvesftw]

Clean that area really good with WD40 and then see where the leak is coming from. Mine went away after retightening the pan bolts, there is a torque sequence that needs to be followed.

[jss06c6]

You really need to clean it up well, then drive it and check it. Critical that you find the source, then we can fix it. My '91 developed a leak at the oil pressure sending unit at the front/passenger side, which blew back across the pan and left a good puddle..

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[TealZR1]

Thanks JSS, mine does develop a good size puddle that came out of nowhere three days ago. I cleaned it up well and the drip ends up at the passenger side rear oil pan. However, I do not have access to a lift and cannot see where it started. At this point a guess.but with this big of a puddle, it has to be worse than a bad gasket or loose bolt on the oil pan

Can I visually access the oil sending unit from above? About where do I start looking for this unit?Thanks in advance

[TealZR1]

I am the original Poster - After getting the car up on the lift at the shop, appears the oil leak is coming from the "oil vent/drain tube" on the oil pan. Did I read that comes from somewhere/something under the plenum? The pic shows it could be there. Thanks
:salute:

[Dynomite]

I am the original Poster - After getting the car up on the lift at the shop, appears the oil leak is coming from the "oil vent/drain tube" on the oil pan. Did I read that comes from somewhere/something under the plenum? The pic shows it could be there. Thanks
:salute:

That Tube is what is called.....the Valley Drain.

You have to remove the Plenum, the Coils, and the Starter to get to the Valley Drain (to clean everything). Good to know your Valley Drain is not clogged. Under the Plenum could be Injector Housing gaskets (tighten Injector Housing Bolts), Crankcase Cover (tighten Crankcase Cover Bolts or new gaskets).

If any bolts appear loose when re-tightening......I just remove the bolts, clean the threads and apply blue Loctite before re-installing the bolts. If I replace the gaskets........I Clean the surfaces and use a bit of Permatex on the gaskets (both sides) for a good oil seal.

I also Block TB Coolant at the Injector Housings and use nothing on the Plenum Gasket since no oil or coolant is involved in that seal.

It is all in my signature ;)

[TealZR1]

Thanks Dynomite, so it appears from what you are saying, I just need to pull the Plenum and start doing the work you recommend for the repair Possible to partially pull the plenum, prop up from the front without disconnecting all the hoses in the back to get to where I need to go? I did that several months ago to fix the famous vacuum leak in the front. Thanks for your help!

[Dynomite]

Thanks Dynomite, so it appears from what you are saying, I just need to pull the Plenum and start doing the work you recommend for the repair Possible to partially pull the plenum, prop up from the front without disconnecting all the hoses in the back to get to where I need to go? I did that several months ago to fix the famous vacuum leak in the front. Thanks for your help!

It would be very difficult to do what I suggested without complete removal of the Plenum which you are almost there anyway. Pull the DIS plugs including the 14 pin Connector with 1/4 inch bolt on rear of plenum and MAP connectors (vacuum and electric). Disconnect the Two vacuum lines each side of plenum possibly including the Purge canister vacuum. And I disconnect the fuel lines (open the gas cap when you disconnect the fuel lines). There are a couple vacuum lines to front of plenum also depending on year. And a couple or three more electric connectors on front of DIS depending on year. And obviously the other external connectors (coolant, Vacuum, electric in front of Plenum and Throttle cables).

Some information for you.......

TOP END RESTORATIONS SUMMARY
Post 62 - 1990 (#2067) LT5 Top End Rebuild (C5 Z06./Wilwood Brakes, SW Headers, Aluminum Radiator) (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581658776)
Post 76 - 1991 (#1427) LT5 Rebuild (C5 Z06/Wilwood Brakes, SW Headers, Ron Davis Radiator) (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581690539)
Post 119 - 1990 (#3032) LT5 Top End Rebuild (Fluidyne Radiator) (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-6.html#post1584987825)
Post 133 - 1990 (#0072) LT5 Top End Rebuild (Ron Davis Radiator) (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-7.html#post1585219749)
Post 230 - 1995 (#0186) LT5 Specific Top End Rebuild (C5 Z06/Wilwood Brakes, Fluidyne Radiator) (https://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-12.html#post1590759172)
Post 261 - 90’ (#8550) Corvette (L98) Modifications (SW Headers, Ron Davis Radiator) (https://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-14.html#post1592505529)

[TealZR1]

Latest Latest Issue-

Just got back from the shop where the car is. Now it won't crank over (all lights are on and getting plenty of power) Can this in anyway be related to the plenum oil leak that is supposed to be draining down the Valley Drain. Perhaps some oil contaminating the starter? A coincidence the starter just went bad? When it rains...
Thanks
:Eagle:

[Dynomite]

Latest Latest Issue-

Just got back from the shop where the car is. Now it won't crank over (all lights are on and getting plenty of power) Can this in anyway be related to the plenum oil leak that is supposed to be draining down the Valley Drain. Perhaps some oil contaminating the starter? A coincidence the starter just went bad? When it rains...
Thanks
:Eagle:

Could be but cannot imagine a couple inches of oil in bottom of valley. You can push start if you have to move the Z....second gear and pop the clutch with key on.

But yes....on the Plenum removal.......always recondition the starter Solenoid points and check starter bearings. Also recondition the Valley Drain and other items mentioned in post above.

[TealZR1]

Could be but cannot imagine a couple inches of oil in bottom of valley. You can push start if you have to move the Z....second gear and pop the clutch with key on.

But yes....on the Plenum removal.......always recondition the starter Solenoid points and check starter bearings. Also recondition the Valley Drain and other items mentioned in post above.

Thanks Dynomite - replacing starter and while plenum is off hoping to repair the oil leak replacing gaskets and tightning bolts as you suggest. Welcome to the ownership of a 26 year old ZR1! Similiar to my 89 Porsche 928 with repairs it seems

[jss06c6]

Keep the faith and smile.. That LT-5 sounds incredible when it's winding up on the road! Small stuff for our '91's. Gotta love working on this piece of art.. I've really enjoyed tuning this engine. Like having two engines under one hood with 16 injectors and a "two stage" intake manifold. Not another one like it on the planet.. Good luck and keep us informed on your progress. Good it's not the oil pressure sending unit.. your repairs are, comparatively easier than that little dude..

[msuhanek]

My ZRI is now in the shop. The mechanic says there is a combination of oil and coolant in the valley drain. He will clean out the valley drain but where could the coolant come from? Thanks


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