Stephenms

I was replacing my hood latch cable and retainers today when I decided to check up underneath my 1987, just for giggles. I've never seen an oil leak like this on any of my cars. The entire rear of the engine. It's not the caked on oil that's pretty dirty from rocks, sticks and kids. It looks like fresh oil. Every two months I'm adding about 2 quarts. The oil drops mostly on the driver side but IS on both sides. My oil filter is covered in it, the torque converter housing is covered in it, the oil pan, nothing on my starter (thank god)

I did replace my intake gaskets not even a year ago. I used a Fel-Pro gasket set that DID NOT come with China wall gaskets so i used black silicone. My vacuum readings are normal for a stock L98 so I wouldn't assume the China wall on the *** end of this engine is failing already. The valve cover gaskets were replaced at the same time. The oil pressure sender was replaced and looked clean. I notice when I take a sharp turn or hit high speeds, I can smell it burning off of the exhaust when I come to a stop or slower speed. The rubber grommet that sits on the passenger side, that recirculates air from the intake into the valve covers or visa versa, leaks oil, and pretty bad too. Crank case ventilation? Is that what it's called? I believe my oil cap does as well.

I am currently thinking of rear main. It's never been replaced and I'm sitting at 108k miles. Unless that recirculating grommet really leaks like a sieve. I guess it could be the rear of the intake leaking, I see oil above the rear main, but the good vacuum makes no sense to me.

Just curious on your thoughts. I'd much rather replace my intake gaskets than a rear main, gives me an excuse to buy new injectors as well. I did spray everything down to pin point where it's coming from AGAIN but man these leaks are hard to keep up with. I will check if my local part store has oil dye as well. When I replaced my intake gaskets a sprayed everything nice and shiny and the oil is back in those spots again, around the rear of the intake and such.

Joe C

a quart per month, is a lot of oil leak! my first guess would be the rear china wall. second, valve covers, third, oil pressure sensors. I know you said you've recently addressed the china walls/intake and VC's, but as they say "s***" happens. long shot - check the oil sensors mounted behind and left of the distributor. I would not suspect the rear main at this point. also, it sounds like you need to replace the VC grommets, and give that oil cap a good look. how is the PCV valve? one quick question - did you use RTV, or a rubber gasket on the china wall? rubber gaskets are strictly a no-no, and when using RTV, strict procedures must be adhered to - all surfaces MUST be squeaky clean, and a 24 hour cure. the "right stuff" seems to be a popular favorite (an quick set RTV type product). good luck...

Stephenms

Pressure sensors are squeaky clean, PCV and grommet was replaced, valves cover gaskets are clean. I cleaned the intake ports and such very very well, with very fine sand paper, a scrapper, and lots of rags. I used black RTV on front and rear. At the time I was hesitant on the rear, I just felt there wasn't enough back there but I guess I decided it was enough after a day of pacing around. I did the 24 hour wait period, then went s retorqued all my bolts, then put the upper intake on.

Basically I cleaned most of the intake stuff off, everywhere around the distributor and part way down, very well. Now that there is oil back in those spots tells me it's intake, AGAIN. But why the good vacuum? I will get new grommets tomorrow just because. And I've been trying to track down an oil cap. All the Auto part stores have a metal cap that does not work, it's not even close yet it's listed as a direct fit for my car. I'll just replace the rubber seal around my current plastic locking cap.

I appreciate the response, very much! It's funny, I told myself "this isn't a job I want to do twice so let's do it right and by the book" looks like I wasn't careful enough😂

Joe C

did you do a good solvent wipe on the china walls and intake manifold mating surfaces before applying the RTV, and did you run the RTV, about 1/2 inch, up, on and under the intake manifold gasket? one thing to check - just above the oil filter, there is a wire-braid ground wire that loops down and goes to the frame (under the battery). does it appear the oil is wicking down the ground wire and dripping on the LH exhaust pipe? BTW, a rear china wall oil leak may not necessarily affect the vacuum readings.

Stephenms

I did not use any solvent, just elbow grease. I applied RTV on the China wall, a small amount around the coolant ports so the gasket wouldn't shift when installing the intake, I don't recall going up the side of the intake, but again, that was a year ago. I do remember feeling uncomfortable with the amount of RTV I had on the China wall. I don't know what I was thinking. I guess I convinced myself it was enough.

As for that ground strap, it's not very thick is it? I noticed it when I was looking at my oil soaked oil filter, but yes, it does have oil on it along with the wire for my O2 sensor.

Joe C

I can't stress enough about having ALL surfaces squeaky clean prior to applying RTV. use acetone or lacquer thinner, and clean the mating surface of the intake (lots of people miss this). pay close attention to the corners of the block (china wall) to cylinder head. make sure those corners are clean and oil free. when you think you have it clean and oil free, go over it one more time!!! i'm fairly sure, running the RTV up, 1/2 inch on to the intake gaskets is covered in the FSM. if you are not sure you have enough RTV, don't second guess. a good 1/4" bead should do it. there is a popular belief about dimpling the china wall, but that is not necessary - having it clean and oil free is the key. sorry that you may have to go through this a second time, but as I said, s*** happens. write it off as a learning experience. again, good luck -

Stephenms

I had spent an entire day cleaning off the surfaces of that intake, I guess perhaps the tools I used didn't do such a good job. Now, I will confirm in the next week if it is in fact my intake, I'm almost positive it is. When I do this over again, should I purchase a new gasket set or can I use my existing Fel-Pro gaskets? Do I have to be cautious with the lacquer thinner? I will most likely do an oil change and purchase new injectors since it'll all be apart. When I apply the RTV, I should apply obviously on the China wall, then up the rear side of the intake going OVER the intake gaskets?

Since I'm going in there a second time, should I replace my hydraulic lifters as well? I know a few of them tick, but nothing drastic. Or should I just top off with some Lucas and wait until they really need to be done.

I appreciate the responses.

scrappy76

Replace the gaskets. do not re-use them especially intake. Run the bead a 1/4" thick along the wall and up 1/2" each side under the new intake gaskets. If you have the coin, would not hurt anything to replace the lifters.

Stephenms

Okay I will be sure to get another gasket. Is Fel-Pro okay?

As for lifters, I have never replaced them before. Just curious on pointers for them. Or if I should just wait. I have the coin right now so I'm just debating. Kinda nervous. I'll flip through my service manual to see what's said about it.

As for the intake torque pattern, my service manual doesn't say to go from middle out. I think it said front two, then all the way down the left bank, then down the right bank. Is that correct?

Stephenms

I'm working out of a 1987 Corvette Service Manual. I have both the SM and Electrical Wiring book.

I will look more into lifters or if it just needs an adjustment. I will be purchasing Fel-Pro gasket sets for the intake. And a set of Bosch 3 series injectors. This should be a fun weekend👍

Joe C

it appears that the intake tightening sequence is the same for 85-88 L98 engines - not sure why it changed for 89-91 - ????

Stephenms

The sequence in your book makes more sense to me, inner bolts working outwards. I mean, it's the same L98. Both aluminum heads. Maybe they realized that's a better tightening sequence? Think I could cause more harm than good buy not following my SM?

Joe C

my experience is limited here. we need some more input from more experienced wrench benders. I've only done engine work on the 1985, 1990, and 96 LT1 model C4's. I tend to agree with you - the 90 sequence does make more sense, and I wouldn't think it would make a difference, but don't go on my word.

Stephenms

Would love some input on this! Does it make a difference? Given I understand the intakes run a bit different but the LT1 pattern makes more sense. If not then I'll just follow the book.

I have ordered hydraulic lifters as well so they will be installed this weekend along with new intake gaskets. I know the saying "don't fix it if it ain't broke" but my lifters make slight noise, could be failing soon, why take the intake apart a third time to replace them, right? Right. Disassembly begins tomorrow night. The lifters will be soaking in 5w-30 oil for the next 24-48 hours.

John A. Marker

May I make a suggestion. The china walls have always been a issue with the SBC including the L98. Years ago the gasket manufactures gave you a rubber gasket with little tabs that fit on both sides of the china wall. They still blew out over time. Then they went to Silicone and that tended to last longer.

I ran across this years ago and have been doing it for years since. Take a metal center punch and use it to dimple the surface of the china wall. This gives the Silicone or other sealant something to grab on to. When I have done this, the china wall seal lasts much much longer. I progressed to doing the same dimpling to the intake where it meets with the china wall.

I would also suggest using Permatex The Right Stuff. You don't have to let it sit 24 hours to cure like Silicone and it can be cleaned up with lacquer thinner.

DGXR

With all that oil coming out of all those places, especially the oil fill cap, it seems to be pushing out of everywhere so I would check the PCV system. Also check for blow-by, or at least do a compression test. Excessive blow-by could pressurize the crankcase beyond what the PCV system can purge. Just a thought.

1985 Corvette

Rear of the intake gave me trouble too. If it leaks back there, it has lots of "pathways" to travel a great distance from the leak source and drive you crazy. I cleaned the hell out of it and even used Right Stuff sealant and I still got a pretty good leak on the rear. Without removing anything, I went back over the area with carb cleaner. Lots and lost of blasting with cleaner and drying it all down back there until there wasn't a spec of anything on the towel. At that point I applied Right Stuff directly to the seam where the manifold and rear wall meet, all the way across. Leak free ever since.

Stephenms

This was actually the first thing I did but saw no results. So I guess the leak is pretty severe.

Since I cleaned up my valve covers (around the oil cap and recirc, I haven't seen any new oil residue spots.

My hydraulic lifters are swimming in oil awaiting installation. A buddy of mine who's helping me with my intake said to use grey silicone from Perma. He said it's much better than the black stuff because it's tougher but still has about the same oil resistance. I took his word for it. Anyone heard of this? He's been fixing 3rd gen camaros since he was 14.

1985 Corvette

You can't go wrong with either sealant. As long as the surfaces are clean. I've used the permex orange sealant with equal results, as long as you get a good quality sealant that indicates resistance to all fluids, you're good. You mentioned oil in the transmission area. Have you taken off the access panel on the bottom to peak in? Only other place I could think of a leak if not the back of your intake is the rear main seal or the cam galley plugs just about the rear main.

Sounds like it may be the rear intake though....once that oil hits the back of the block, it can travel downwards on the passenger or driver side and go everywhere.

Stephenms

I did check, yes, pretty clean except the usual dirt, rocks, sticks and kids. I had cleaned everything and rechecked a few weeks later, just as bad as before I cleaned it. But you're right, oil goes everywhere. Burns on the exhaust, tranny casing, oil filter, freeze plugs. I had oil pushed all the way back to under the passenger floorboard/fiberglass and onto my paint right under the passenger door.