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  1. #1
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    Default New motor, Mystery oil leak :(

    I recently built a 347 stroker motor for my 79 pace car and after I got it running I noticed an oil leak coming from the back of the passenger side head. I used afr heads and fel-pro Mls gaskets. This leak is not coming from the intake. I can hold a q tip in the corner of the intake while it's running and it's dry while I watch oil drip from the bottom of the head. I'm really stumped on this one. My block is even decked to a near mirror finish by yours truly and same can be said for the heads. Any ideas?

  2. #2
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    Valve cover comes to mind .
    clowns to the left of me , Jokers to the right

  3. #3
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    Definitely not valve covers either, the head its self is dry, the block is where I'm seeing the oil.

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    I had something similar years ago on a 66. It would smoke out of 1 side of the exhaust. I could not find a leak anywhere. One day a friend watched it for a long time while it was idling. He saw a drop of oil (Mobile 1) leak out the bottom of the valve cover, hitting the hot header, speeding up to the bottom and the drop was sucked in around the collector (slightly leaky gasket) to be burned. It appeared that the engine was burning a massive amount of oil when it wasn't, but it sure smoked like mad. Evidently those TFS exhaust ports were a little taller than stock, keeping the valve covers from tightening all the way down because they were on the header flange. Thicker gasket solved the problem.
    I learned to check the simple things first before doing more drastic things.

  5. #5
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    I've already checked all the simple things, I've watched it while idling and I can watch a pool form above one of the bellhousing bolts, but it does not pool on the top of the motor behind the intake, it's about halfway down the head, about where the oil drain back hole is in the block. I'm pretty sure it's coming from here but I can't figure out why. I don't want to tear my head off and not be able to fix anything.

  6. #6
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    I believe MLS head gaskets require a pretty specific surface finish to seal properly. I know you say a mirror finish, but are you sure it's dead flat?polished by hand and not finished on a mill could be a bit of an issue.
    1983 Mustang G.T. No-option stripper- I like strippers.
    5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.

  7. #7
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    Not sure what you mean polished by hand, I'm a machinist so I milled my block and heads to the apropriate finish required, hand polishing a deck surface would probably do more harm than good.

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    FEP Member brianj's Avatar
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    Quote Originally Posted by Leroy Jensen View Post
    Not sure what you mean polished by hand, I'm a machinist so I milled my block and heads to the apropriate finish required, hand polishing a deck surface would probably do more harm than good.
    Ok, gotcha. I didn't know you were a machinist. Typically, if someone says something like that they got a near mirror finish on the deck, I picture someone with a can of brasso and a rag, and I cringe! Lol This is not uncommon with the MLS gaskets, unfortunately. They are highly unforgiving of finish and fitment on both the deck, and the intake side. It's usually (from what I've seen and heard from others) wicking over from the intake side, although some did come from the deck itself. Are you planning serious boost, or why did you go with MLS gaskets?
    Last edited by brianj; 07-23-2017 at 09:52 AM.
    1983 Mustang G.T. No-option stripper- I like strippers.
    5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.

  9. #9

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    I've always had good luck with a black light and oil dye.

  10. #10

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    sometimes with MLS gaskets you need to put a dab of RIght Stuff on each upper corner where the head meets the intake. Have the heads or intake been milled? What thickness head gaskets did you use.

  11. #11
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    Heads have been milled to the appropriate finish required for MLS gaskets, the leak is not coming from that far up on the head either, more down by where the top row of head bolts are, I think I found the problem though. There was a small amount of corrosion around the oil drain back hole in the block, pissibly causing oil the get around the seal for that hole. I pulled the head, put a small amount of silicone in the corroded spot, and coated the head gasket with copper spray before putting the head back on, hopefully this fixes the leak!

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