390 Oil Leak Blues

pilotjock · Feb 9, 2009

I have a 71 F100 with a 390. The motor was rebuilt about 5k ago, and not long after started leaking oil from the back of the motor, most prevelant on the passenger side. I figured it was a rear main seal problem. I replaced it twice with no effect. Both times with neoprene seal. I inspected the crank, it was in good shape with ////// marks. I thought about the intake causing the leak, so redid it with no effect on the leak. Any ideas where my problem is? Could it be the camshaft/oil gallery plugs or am I way off on that? If so, would the flylwheel be covered in oil, cause its not? Some say I should live with it, but I don't like to see puddles under my truck or tons of oil grease underneath. I appreciate any ideas.

Tyler

jwko · Feb 9, 2009

Could be coming from the rear intake area.

pilotjock · Feb 10, 2009

Like I said initially, I redid the intake with no results. It seemed to have a good seal before, but I gave it a try anyway. Any ideas on the oil gallery plugs being the source?

kdtrucker · Feb 10, 2009

Are you sure it's coming from behind the motor? Have you checked the valve cover gaskets?

Also make sure the intake is sealed,...not just on the flat edge of the block but the corner where the intake gasket meets the flat edge gasket. If you are using silicone or right stuff make sure that you have enough to seal the open gapped area.

jonnydesert · Feb 10, 2009

try adding a tracer additive to your oil. you can get it at any parts store. clean any excess grease off the back of the engine. run it for a day or two, get back under with an ultraviolet or "black light" and the tracer will shine green or light blue and you can follow the trail to the source of the leak

Tom Krukowski · Feb 20, 2009

I am currently investigating the same problem on my 1962 Mercury 390. I just rebuilt and installed the engine and its having the exact same problem and symtoms you are having. I dont understand how the flywheel can remain dry and still have oil leaking from inside the bell housing.
Ill let you know what I find. I dont think I have a choice but to pull the trans out at this point. Everything outside the engine is dry except the starter which appears to be supplying a partial exit for escaping oil.

kdtrucker · Feb 22, 2009

another item you might check, besides the oil galley plugs, check the cam plug it might be leaking from there. I always install it cup side in, and for a sure seal, a little gasket sealer on the edge. are you running an automatic or standard?

cyclone gt · May 13, 2009

Do yourself a favor and pull your trans and replace the oil plugs. I had my engine rebuilt and started it and oil was everywhere. Put in a new rear main seal and same thing. There are 3 plugs and one was leaking. I'm going to replace all 3. i dont like the way they look

390 Oil Leak Blues

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