I am making a post about this because I have exhausted all of the possible reasons for this oil leak that I can come up with. I have a 1978 351m swapped into my 1980 f150, the oil leak cause me to loose about 1 qt of oil every 100 miles. Oil is getting all over the oil pan, front cross member as well as getting on the passenger side frame and shock absorber. I replaced the front main seal along with the entire timing chain cover, wich seemed to have no effect, then I replaced the oil pan gasket seal with a new rubber/cork composite seal and the necessary rtv sealant. The leak is the same as before I started. All I can think of is that the oil pan is warped and I need to order a new one. However if this were the case it dose not explain how the oil is seemingly getting sprayed onto the passenger side frame and wich is something I have only ever seen with bad front main seals; but as I previously mention, it has a brand new front seal wich does not appear to have any oil leaking from it. Any insight as to something I may have overlooked or anything I may be unaware of when it comes to these engines would be appreciated. I should mention I switched from 10w-30 synthetic to 10w-30 non synthetic oil to see if it had an effect on the leak and it did not.
-(I also posted this thread on the bullnose forum since the truck is a 1980 chassis)

 

It could be leaking from the front of the intake down the front of the engine.

 

Mine leaks at the rear of the intake some.

 

Before you get too much deeper into this, check your PCV setup. If it's not working properly, excess crankcase pressure will continue to blow out gaskets and seals. If your PCV system is working properly, and you still have a lot of blow by and crankcase pressure, then you probably have worn out piston rings, and out of round cylinder walls.

 

X2 check PVC system.

And did you flat edge check the oil pan bolt rows? Some times the oil pans (and the valve covers) bolt rows (all the bolt holes in a row) get bent from the bolts getting over tightened. With the pan off you need to use a 6" steel ruler to flat edge check the area around where the bolts going in, for being bent in ward. Tap Tap make it flat. Also check for cracks around the holt holes.

A drop of oil once in the wind can go all over and make quite a mess and make the actual leak point hard to find.

 

As long as you have a clean breather don't worry about crankcase pressures.

 

leak around a valve cover will travel a long way as well.

 

Are any of the dowels that locate the front cover missing? Those holes go right thru the block, & can pump out an amazing amount of oil if the dowels are missing.

 

If you are referring to the dowels that that help align the timing chain plate then yes they are missing, I was unaware this could cause an oil leak?

 

I should have mentioned in the original post that I have checked pcv and it is working.

 

Yes, those are the ones. Look under & behind the alternator, I think there is one there. Poke a wire in the hole, I'll bet it will go way in. Clean the hole really well with brake clean, squirt some silicone in the hole, let it set over night. If luck is on your side the leak will be solved.