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4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 10-10-2016
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Join Date: Aug 2016
Location: La Grange Park, IL
Posts: 20
oil leaking only when engine is running

Hello i just got my 4.0l back in the truck and running but i am loosing a lot of oil from the back of my engine. it only leaks when the truck is running does this mean that its my rear main seal leaking or could it be my gasket between my block and aluminum ladder frame?

I am guessing its my rear main seal on the fact of that it only leaks while its running and the rear seal will get pressure from the rear bearing.

If it is the rear seal can i drop the trans out and replace it with out removing the engine?

Any help greatly appreciated.
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Old 10-11-2016
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Join Date: Jan 2014
Location: Vancouver, BC
Posts: 7,864
Yes, rear main is the problem

Yes, drop the trans and remove flexplate or flywheel to replace rear main.

After old seal is out, rotate the crank and look for scratches, even a small scratch well ruin new seal in a short time.

You can get sleeve kits if crank is scratched, they come with a sleeve that goes over the crank and a slightly larger seal that rides on the smooth sleeve.
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Old 10-19-2016
Thread Starter
Join Date: Aug 2016
Location: La Grange Park, IL
Posts: 20
Ok so over the weekend I did a little poking around under my truck and determined it is not my rear main seal leaking i pulled my starter and looked inside my bell housing and there was no oil to be found in there.

So today when I was on my way into work i put my foot to the floor and when i did a lot of oil must have leaked out because when i parked and looked under my truck my whole trans was dripping with motor oil and i could clearly see my main wiring hares on the back of my block is wet. I took a mirror and looked at the back of the valve cover and its bone dry so now I am thinking it might be my driver side head gasket.

Is this possible i would think that if my head gasket was bad it would leak oil into the cylinder and burn it up not leak out the back? there is no smoke coming out of the exhaust at an idle or when at 2,000 rpm. I do see smoke in my rear veiw mirror when i get up to about 3,000 or 3,500 rpm but i think its oil leaking down onto my exhaust and burning off.
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