Oil leak.

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Joel Chapman

Joel Chapman

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So I recently put a rebuilt 360 in my 71 dart and noticed a oil leak coming from the back of the engine. What’s weird about this leak though, is has only happened once. I am pretty sure it happened after the longest this engine has run since I’ve installed it, but that’s it just that once. Is it just part of the seals and everything that’s goes along with breaking in and engine or is there more to it than that?

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Could be from several places. The oil sending unit its self, or where it threads in, the back of the intake not sealed up (I had this issues, only leaks when driven), rear main seal, Valve covers, PCV Valve seal or breather seals or a plug in the back of the block just to name a few. Bottom line is your going to need to trace it.

Do you happen to have aftermarket intake? Almost no valve cover including stock clear an aftermarket intake, they and/or the valve cover almost always need massaged or spacers installed.
 
dano said:
Could be from several places. The oil sending unit its self, or where it threads in, the back of the intake not sealed up (I had this issues, only leaks when driven), rear main seal, Valve covers, PCV Valve seal or breather seals or a plug in the back of the block just to name a few. Bottom line is your going to need to trace it.

Do you happen to have aftermarket intake? Almost no valve cover including stock clear an aftermarket intake, they and/or the valve cover almost always need massaged or spacers installed.
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Aftermarket intake. I checked where the oil sending unit plugs in and it was dry. Every where I can see on the top of the engine was dry. From what I can tell it’s coming from somewhere in the space that is covered by the bellhousing.
 
Oh, I forgot to mention oil filter and/or oil filter adapter. Its amazing how fluids can track along the engine.

Have you removed the trans shield or is that the type you need to remove the starter too?
 
Oil filter was dry. I just changed the break in oil yesterday. I’m not sure bout the shield, but will check.

Youu are right is pretty amazing how it will travel all over the place. What has me puzzled with this one though was that it was just one time that it leaked or at least leaked enough to show.
 
Could be crankcase pressure pushing oil past the seals. Are you using PCV valve or breathers.
 
Joel Chapman said:
So I recently put a rebuilt 360 in my 71 dart and noticed a oil leak coming from the back of the engine. What’s weird about this leak though, is has only happened once. I am pretty sure it happened after the longest this engine has run since I’ve installed it, but that’s it just that once. Is it just part of the seals and everything that’s goes along with breaking in and engine or is there more to it than that?

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I just recently installed my freshly rebuilt 408 a few weeks ago. Broke it in and ran it around town a few times testing and tuning.Everything was good.I went on a longer highway run last weekend only to develop an oil leak like yours. Turns out I needed to retorque the oil filter adapter bolt. Oil would come out and down the oil pan rail and settle exactly where your leak is shown. It’s not uncommon to have to go back and re tighten gasket surfaces after a few heat cycles.RJ
 
Swingin Chrome said:
I just recently installed my freshly rebuilt 408 a few weeks ago. Broke it in and ran it around town a few times testing and tuning.Everything was good.I went on a longer highway run last weekend only to develop an oil leak like yours. Turns out I needed to retorque the oil filter adapter bolt. Oil would come out and down the oil pan rail and settle exactly where your leak is shown. It’s not uncommon to have to go back and re tighten gasket surfaces after a few heat cycles.RJ
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I will give that a try, thank you!
 
thats the lowest spot on the engine all leaks above will end there , does look like the rear main to me though.
 
dogbreath said:
thats the lowest spot on the engine all leaks above will end there , does look like the rear main to me though.
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Swingin Chrome said:
I just recently installed my freshly rebuilt 408 a few weeks ago. Broke it in and ran it around town a few times testing and tuning.Everything was good.I went on a longer highway run last weekend only to develop an oil leak like yours. Turns out I needed to retorque the oil filter adapter bolt. Oil would come out and down the oil pan rail and settle exactly where your leak is shown. It’s not uncommon to have to go back and re tighten gasket surfaces after a few heat cycles.RJ
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Retorqued the adapter bolt and it was lose. Put about 20 miles on it today running around base and it still had a little on the trans. Possibly left overs from the adapter bolt being lose?

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Joel Chapman said:
you double checking the rear of the engine or is it coming out for other issues as well?
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Coming out just for the oil leak. Got too much invested to park a "New" Car at $40k and have a oil leak. That's not how I play at this level of a restoration.
 
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These old engines all have split rear main seals, not the one piece like the Vortec Chevys and later Fords used, so leaks are easier to get in that area. I've torn apart some remans where the seals were put together dry as a bone and that's not the right way to do it. There's the trick of "offsetting" the rear seal thinking that somehow that will stop it from leaking. I've never done it, and never had a problem there. I wish someone would tell me how that will help stop a leak. It won't. In fact, IMO, you have more of a chance, because it's tougher to put a dab of RTV on the ends of the seal where they butt together. Offsetting the seal makes zero difference in how it fits together, it simply changes the location of the joint in the two halves. If it's gonna leak, it's gonna leak, regardless of where the joint is. I want the joint where I can SEE IT and where I can GET TO IT easily. I also put a light film of RTV from the seal halves out between the halves of the rear main cap to block joint as well. I've never seen that done on any reman I've ever torn down and so far, I've never had one leak I put together. You have to be careful though, because as mentioned, there are a couple of places up higher that can mimic a rear seal leak. Oil sender, distributor o-ring. Even an intake gasket or valve cover gasket. I've even seen a head gasket droolin oil down the back of the engine....and dont forget the camshaft plug in the back of the block and the oil galley plugs if there are any.
 
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