Troublesome Oil Leak

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JeremyAB95

JeremyAB95

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I have a rebuilt 340 and went to do engine break-in and had a couple leaks that I can't quite solve. One appears to be coming from the rear of the engine around the distributor o-ring as well as the fuel pressure sending unit, and the other is coming from some mysterious location near the front. Valve cover gaskets are dry. When viewed from the front, the passenger side head has a little bit of oil near the bottom left corner of the head. I tried re-torquing the head studs on that side per Edelbrock's procedure listed in their instruction manual for the Magnum aluminum heads. I also noticed oil pressure was reading around 60 - 70 psi at 2500-3500RPM and thought that seemed a little high. Also worth noting that the oil level seemed high when I checked the dipstick - have a stock pan and put in 5 quarts with the new filter. Could either of those be a contributing factor? I can go out and get pics later but just wanted to pick your brains. Leak is substantial enough that both locations made little pools about as big as a sheet of printer paper under the car.
 
JeremyAB95 said:
One appears to be coming from the rear of the engine around the distributor o-ring as well as the fuel pressure sending unit,
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Where is this mysterious FUEL-pressure sending unit that somehow leaks OIL? If you mean the factory OIL-Pressure sender, they are known to leak as they get older. It may be the guilty leaker back there for both leaks. You cannot isolate this device because it grounds to the engine block thru the threads. Well you can but you'd have to engineer a new ground. But these senders in my experience, leak thru the lower perimeter crimp as often as not.

Have you got a working PCV system? If not, then; I would do a CC pressure test
and probably, a compression test.
 
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Crankcase pressure building up, pushing the oil out the front and rear seals.

Engine not broke in yet, need to get those rings seated so your compression quits going down past your rings into the crankcase and building pressure.

Bring the engine up to temp. Then go and work it hard for 1/2 hour, but don't abuse or beat on it.

Need to expand out those rings during a good workout and mate them to the cylinder walls.

Then change oil and filter and go drive it like you normally want too. Clean up your oil leak areas and hopefully things will dry up and stay clean for you.

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I just finished chasing the same kind of leak. After doing all the easy stuff it turned out to be the china wall. Put in a new intake manifold gasket and sealed the front and back really well and finally it stopped leaking oil.
 
Details about the rebuild would probably help! Maybe even some pictures.
 
AJ/FormS said:
Where is this mysterious FUEL-pressure sending unit that somehow leaks OIL? If you mean the factory OIL-Pressure sender, they are known to leak as they get older. It may be the guilty leaker back there for both leaks. You cannot isolate this device because it grounds to the engine block thru the threads. Well you can but you'd have to engineer a new ground. But these senders in my experience, leak thru the lower perimeter crimp as often as not.

Have you got a working PCV system? If not, then; I would do a CC pressure test
and probably, a compression test.
Click to expand...

Crap! Sorry, brain fart. Meant the oil pressure sending unit at the back near the distributor. I have one of those Mopar chrome push-in breathers on one valve cover and a PCV on the other. Oil pressure sending unit is an intellitronix one for their electronic gages so I don't know if that's just a crummy part. That may explain the leak at the back of the engine but there's still the matter of the other leak near the front that has me baffled. Where would the best place be to read crank case pressure were I to test it?
 
69FBCuda said:
Details about the rebuild would probably help! Maybe even some pictures.
Click to expand...
CUDA69 said:
I just finished chasing the same kind of leak. After doing all the easy stuff it turned out to be the china wall. Put in a new intake manifold gasket and sealed the front and back really well and finally it stopped leaking oil.
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I did a little research and started digging through other threads and I am wondering if this is what's causing my leak on the front of the engine. It seems wet near the corner of the head where the intake manifold gasket is supposed to meet up with the RTV gasket goop, at least I think it does. From there a little bit seems to run down along the timing cover and pools up in one of the freeze plugs, and the bulk of it runs along the head until it drips off from there. I don't think it's the timing cover given that some of the oil can be found above the cover. Hopefully it's not the head gasket itself. Valve cover gaskets seem dry.

Got some pictures, not sure if they are the most helpful.

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leak3.png
 
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Oil leaks can be very agrivating or frustrating. Some answers to them are obvious, other times, not. I have always had issues with rear mains, torn down and tried other people's suggestions. They worked, until they didn't. A friend said, Get used to it. I bought the ME Wagner adj PCV valve thinking, what the hell, can't keep doing the same thing over and over and expect different results. Well, the adj valve dried up 2 different engines rear main oil leaks. So I expect that it will help or stop the other little annoying seepage around the engine that are not real oil leaks. It works for me, maybe the adj PCV valve can help others. Yeah it's pricey and for different valve cover combinations, you do have to get different rubber inserts for the pcv valve. The valve is 3/4" vs Mopar 1/2". The inserts are available, I have the numbers for Mopar cast performance and stock stamped steel covers that have a factory pcv valve. There rubbers are available from Summit. Gene at ME. Wagner is great to deal with.
 
My money would be on the china walls. When I installed the 4-barrel on my 318, I didn't use a tall enough bead of rtv on the china walls and after several heat and cool cycles I was leaking oil out the back. After getting advice on here, I was able to "fix" the leak without having to pull the intake again and start over. I pulled the distributor and oil pressure line and cleaned the back of the intake and top of the block with brake clean thoroughly and then basically placed a "bead" of ultra-black along the intake to block joint and smoothed out with a rubber-gloved finger. No leaks since and I've probably driven a couple thousand miles. I found that some guys actually fill any remaining intake to block gap with rtv after installation and before the engine is ever run which I will do in the future.
 
I am thinking it may be the China walls. I tried the dye out to help me find the leak and it seems like there's a small one in the front corner where the pax side head meets the intake, and then the back seems to be leaking all along where the intake seals against the china wall. I thought I was pretty generous enough with the grey RTV gasket maker when I was assembling this thing. May need to try degreasing better or something when I redo it. Rear main does not seem to be leaking at least. I'm hoping the head gaskets are not a problem and it's just the intake. Thoughts?

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Engine dye is cool, but after a short time, your whole engine will be florescent!
 
I NEVER use RTV "only" on the China walls. use the gaskets as provided with gasket set and RTV the corner seams, a slight smear across with the finger before you set the intake in place if you must but do use those included end wall gaskets or else send them to ME!!! These are Mopars I don't use "chevy service info" on them... I know. GM just loves their gasket goo.....
 
Want to use Brake Parts cleaner on all sealing surfaces to remove any trace of an oil film before you apply the RTV gasket maker.

Otherwise the RTV has nothing to adhere to and the oil will seep by.
 
JeremyAB95 said:
I am thinking it may be the China walls. I tried the dye out to help me find the leak and it seems like there's a small one in the front corner where the pax side head meets the intake, and then the back seems to be leaking all along where the intake seals against the china wall. I thought I was pretty generous enough with the grey RTV gasket maker when I was assembling this thing. May need to try degreasing better or something when I redo it. Rear main does not seem to be leaking at least. I'm hoping the head gaskets are not a problem and it's just the intake. Thoughts?

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I found the grey rtv doesent really set up hard like other sealants. I bought it because there was no ultra black on shelf.

i had a 318 poly that would not stop leaking at back china wall. I put shop vac on crankcase vent and put sealant across the outside. I cleaned it first.
That finally sealed it.
 
George Jets said:
Want to use Brake Parts cleaner on all sealing surfaces to remove any trace of an oil film before you apply the RTV gasket maker.

Otherwise the RTV has nothing to adhere to and the oil will seep by.
Click to expand...
Would you recommend any light sanding? I saw some other threads recommending making a little crosshatch pattern on the China wall with 220 grit.
 
Thanks everyone for the helpful replies. Almost certain it was the china walls, found oil in the corners when I tore into the engine today and got the intake off. Used damn near a whole can of brake cleaner degreasing everything. I switched from the gray gasket maker to the ultra black RTV, and I made sure to do a more thorough job overlapping the corners under and over the intake gaskets. Fingers crossed I don't have the pleasure of trying a third time.
 
Tooljunkie said:
I found the grey rtv doesent really set up hard like other sealants. I bought it because there was no ultra black on shelf.

i had a 318 poly that would not stop leaking at back china wall. I put shop vac on crankcase vent and put sealant across the outside. I cleaned it first.
That finally sealed it.
Click to expand...
If you use the Ford brand grey RTV, you can glue the oil pan on with no gasket, screw the bolts in until it dries, then once dry remove the bolts, throw them away and it will never leak and you'll have to pry it off with a prybar the next time it has to come off and the oil pan probably won't live through it. Ask me how I know. lol
 
RustyRatRod said:
If you use the Ford brand grey RTV, you can glue the oil pan on with no gasket, screw the bolts in until it dries, then once dry remove the bolts, throw them away and it will never leak and you'll have to pry it off with a prybar the next time it has to come off and the oil pan probably won't live through it. Ask me how I know. lol
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Elastomeric sealant. Tough stuff. Is odd job sealant still available? I bent a diff cover after using that stuff. Cant get around here.
 
Tooljunkie said:
Elastomeric sealant. Tough stuff. Is odd job sealant still available? I bent a diff cover after using that stuff. Cant get around here.
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I'm not sure. I think the right stuff is pretty comparable from what I've heard. I've never used it. All I want is something that'll SEAL, not tear crap up coming apart. LOL
 
JeremyAB95 said:
I am thinking it may be the China walls. I tried the dye out to help me find the leak and it seems like there's a small one in the front corner where the pax side head meets the intake, and then the back seems to be leaking all along where the intake seals against the china wall. I thought I was pretty generous enough with the grey RTV gasket maker when I was assembling this thing. May need to try degreasing better or something when I redo it. Rear main does not seem to be leaking at least. I'm hoping the head gaskets are not a problem and it's just the intake. Thoughts?

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In the 5th picture down, it sure looks like the rear joint between the intake and that rear china wall is the source "back there".
 
Tooljunkie said:
I found the grey rtv doesent really set up hard like other sealants. I bought it because there was no ultra black on shelf.

i had a 318 poly that would not stop leaking at back china wall. I put shop vac on crankcase vent and put sealant across the outside. I cleaned it first.
That finally sealed it.
Click to expand...

Agreed My local auto parts were out of black as well. I found the grey to be runny when applied compared to the ultra black. I will not use the grey anymore for the intake.
 
1973dust said:
My money would be on the china walls. When I installed the 4-barrel on my 318, I didn't use a tall enough bead of rtv on the china walls and after several heat and cool cycles I was leaking oil out the back. After getting advice on here, I was able to "fix" the leak without having to pull the intake again and start over. I pulled the distributor and oil pressure line and cleaned the back of the intake and top of the block with brake clean thoroughly and then basically placed a "bead" of ultra-black along the intake to block joint and smoothed out with a rubber-gloved finger. No leaks since and I've probably driven a couple thousand miles. I found that some guys actually fill any remaining intake to block gap with rtv after installation and before the engine is ever run which I will do in the future.
Click to expand...

my China wall in the front is leaking a bit after head/ intake swap. Little bit of oil lays on the top of timing cover after a pass, just enough to where it shows up a little on a small piece of paper towel. Gonna brake clean it good, and smooth in a bead of right stuff and let it set up, should fix it. Not really much of an issue, but…
 
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