New Motor: Strange Oil Leaks

[btwick]

Have a newly built 383 sbc motor on a run stand with 10-15 minutes of run time. Before it goes in the car, would like to know what is causing four oil leaks between the head and block on the four corners - cyls 1, 2, 7, 8.

No evidence of leaking from the intake manifold front and rear seals or the valve covers.

Could it be not enough sealant on the head bolts? Used RTV. Any other sources of oil to these locations that could be the culprit?

Also posted in the Corvette Forum with pics here: https://www.corvetteforum.com/forums/c3 ... 1604369635

Thanks in advance for your help!

[i82much]

PCV? i had some weird leaks on my Pontiac. I bought a manometer and measured the crankcase vacuum, had very little using a factory PCV valve. Switched over to a different factory valve and it improved. Both valves were brand new, just different calibrations.

Later I put on one of those ME Wagner adjustable units and measured it again and it improved even more.

[BOOT]

Was the block decked or heads resurfaced? Did you use MLS head gaskets?

[btwick]

Hi,

Block was decked and heads were checked for warpage, but not resurfaced. They are Promaxx 2169 aluminum. Used Felpro 1010 head gaskets, which are the .039 compressed size for SBC.. Maybe incompatible head gaskets with the Promaxx heads on the block? Block is a 86-99 one-piece rear main seal gen 1 sbc block.

[In-Tech]

Quite common to leak in the upper corners between head gasket and deck, a small smeer of ultra grey does wonders. A small blob in those corners when installing the intake is mandatory.

[btwick]

Quite common to leak in the upper corners between head gasket and deck, a small smeer of ultra grey does wonders. A small blob in those corners when installing the intake is mandatory.

Thanks. Quite certain it is not coming from the upper corners of the heads, where they meet the intake manifold. Liberal amounts of RTV there, and would see it running down the head gasket on the sides of the heads to get to the bottom corners. No trace of that. These leaks are from the head gasket down by the 1, 2, 7, 8 cyl head bolts.

Can't think of any source of oil to come from the head gasket there. Mystery for sure.

[BillK]

Go to your local parts store and buy a bottle of UV leak checking die and put in the oil and run it for a while. If you dont have a UV flashlight buy that also while you are at the store. It will show you where it is coming from.

https://www.autozone.com/test-scan-and- ... 667635_0_0

https://www.autozone.com/test-scan-and- ... 424631_0_0

Head bolts dont leak oil, they leak coolant. I know you disagree but I am also betting on the corners of the gaskets. I think I remember having one engine where the head gaskets did not go all the way to the end of the head up near the corner and caused a leak but I think it was a Big Block.

[btwick]

Go to your local parts store and buy a bottle of UV leak checking die and put in the oil and run it for a while. If you dont have a UV flashlight buy that also while you are at the store. It will show you where it is coming from.

https://www.autozone.com/test-scan-and- ... 667635_0_0

https://www.autozone.com/test-scan-and- ... 424631_0_0

Head bolts dont leak oil, they leak coolant. I know you disagree but I am also betting on the corners of the gaskets. I think I remember having one engine where the head gaskets did not go all the way to the end of the head up near the corner and caused a leak but I think it was a Big Block.

Thanks Bill. Yes, have pics of the leaks on the Corvette forum link using dye and UV light. Link in first post. Not sure how to post pics here.

But, yes, have tiny amounts of oil from the Chinese walls on the intake down the ends of the head gaskets to the spots indicated. Could be some wicking movement of oil starting up there and accumulating down in the corners. Looks so small that hard to imagine it would create the leaks indicated.

Thinking you are right, and will be pulling the intake tomorrow and looking for any breaks or bubbles in the RTV on the ends of the manifold. Will report back.

[6.50camaro]

I will second what BillK said. A couple years ago I had a sbc that leaked as described on the passenger side rear. The head gaskets were about .090 short from reaching the end of the cylinder head . used plenty of rtv in this area 3 of the 4 corners sealed. But 1 rear corner did not, the engine was in the car played with valve covers for hours .Finally Cleaned things off with solvent to remove oil residue . held a white paper towel in the rear corners, while idling the engine finally found it. Dan

[BOOT]

Had some heads done by a new-to-me shop and one side leaked in the rear corner(tip) of the headgasket. As others said I'll use some RTV on the tips from now on when installing the heads to save me trouble of pulling one But I've never had that problem before. Also think I read it's a common problem with MLS head gaskets and why I asked.

[rustbucket79]

The only places oil can leak on a SBC is the valve cover gasket and rails of the block deck that lead to the intake end rails. As mentioned the intersections of the intake gaskets/head gaskets/end seals is a common leak point. Oil can wick along the head gasket and drip at the low spots.

I would be tempted to brake clean and blow out those intersection points and squeeze some Right Stuff in the areas and a bit lower in the gaps between the heads and decks, let cure and run again.

[rustbucket79]

Had some heads done by a new-to-me shop and one side leaked in the rear corner(tip) of the headgasket. As others said I'll use some RTV on the tips from now on when installing the heads to save me trouble of pulling one But I've never had that problem before. Also think I read it's a common problem with MLS head gaskets and why I asked.

Yep first time I put a SBC MLS gasket on I wondered why the hell are the ears .060” short. Since I always put a thin bead in that area on both sides of the gasket “just in case” there is no problem. If you plunk them on dry and put the heads on without catching the gap, you’ll be screwed.

[btwick]

Had some heads done by a new-to-me shop and one side leaked in the rear corner(tip) of the headgasket. As others said I'll use some RTV on the tips from now on when installing the heads to save me trouble of pulling one But I've never had that problem before. Also think I read it's a common problem with MLS head gaskets and why I asked.

Yep first time I put a SBC MLS gasket on I wondered why the hell are the ears .060” short. Since I always put a thin bead in that area on both sides of the gasket “just in case” there is no problem. If you plunk them on dry and put the heads on without catching the gap, you’ll be screwed.

Hmmm. Bit of a tangent here but was not picking up the comment about MLS gaskets. The gaskets I used with ProMaxx alum heads was FelPro 1010 composition gaskets. Says steel core, but am I using the wrong head gaskets?

Back to the leak. Pulled the intake manifold, no smoking gun.

Two possible fixes. One is the corners of where the intake manifold, block, and heads all meet. I did use RTV on all corners, but possibly not enough beneath the intake manifold gasket from what I see now. Ample amounts on top of the gasket where the manifold sits and plenty on the china walls. But, still hard to image so little trace of leaking up there and down the end of the head gasket to create the volume at the bottom.

The second issue could be the thin parts of the head gaskets where they meet the intake manifold as mentioned above. Mine go up to the edge of the head, but I didn't put sealant anywhere on the head gasket. It could be flowing out to the outsides of the heads there somehow.

So, options are reseal the intake with emphasis on ample RTV in the corners, both at the top and bottom of the gasket and china walls, or pull the heads. Really don't want to pull the heads again, obviously. Thoughts?

[af2]

That is the reason I don't use end gaskets, 1/4" rtv along the front and rear rails up a bit on the water holes wipe off excess after you install the intake, let it cure and you are good to go.

[rustbucket79]

Nothing wrong with your choice of head gaskets. Before you go any further take an air nozzle and blow along the gasket seam on the fronts and backs of the heads with a clean rag to catch the spray, that’ll give you a better idea of where the oil is coming from.