MASSIVE oil leak mechanic can’t find

[took-the-red-pill]

1988 OMC 4.3 Cobra. Runs like a Swiss watch. Tons of power in my 16’ boat.

Leaks engine oil at a rate of about 1L per hour of driving under load, tubing, water skiing etc.

Oil leak is all inside. Boat fills with it and I have to drain into a bucket so I don’t pollute the lake.

Remedies so far:
- Mechanic pulled the motor and there was a bit of normal sweating but he replaced the rear main seal anyway. Of course he did a new pan gasket.
- He ran it outside the boat for about an hour. Zero leaks.

But when I drop it in the water and run it up to 3000 - 3500 even while not pulling a skier, the leak was back.

He’s at a loss. He says everywhere that could be leaking has been addressed. Obviously not.

Top of engine is clean, under exhaust manifolds is clean. From looking/feeling, I can’t find any oil drops on the pullies, no oil on the bottom of the oil pan that I can feel.

I put a Go Pro under there at passenger side, front of engine. I ran it but couldn’t catch it leaking.

Any ideas would be greatly appreciated.

Thanks
Keith

Thanks.
Keith

 

[Scott Danforth]

Was there rust on the pan?
How is the back of the block, just to port of the distributor? Many times the oil pressure sensor can leak

 

[took-the-red-pill]

HI Scott,

Thanks for taking the time to help out. I was just under there with a camera and do not see any rust on the pan. I also went around with fresh paper towel.

Top of motor near distro is clean. I can’t find any as I go down the port rear of the motor. In fact I can’t find any fresh oil on port side. I can’t get any fresh oil going down rear starboard either, but

The only place i can is on and around the starter and its wires, and the oil pan beside the starter. Not a large volume, Just a bit, but I haven’t run it in 3 days.

If it’s coming down by the starter, would that suggest head gasket? A seal between an oil jacket and outside?

To repeat, he didn’t get anything while it was out of the boat running, but as soon as I put it under load and run it up to 3000 I begin to get this leaking issue. So it seems it requires the 40LB of oil pressure to leak

Thanks
Keith

 

[took-the-red-pill]

By the way, if the oil sensor is the chrome thing on TOP of the engine right beside the distro, about 2” diameter and 2” high with a wire on the top, it is completely clean all around that area And below.

 

[Lou C]

Ok one thing easy to miss is a rubber plug that’s used in a marine application when the dipstick goes to the bottom of the pan and not into the block. A little rubber plug just above the oil pan in front of the starter.

 

[Redrig]

throw some dye in the oil and take it for a ride under load . should leave a nice trail wherever its coming from

 

[Bt Doctur]

Where is the dipstick? f thru the pan you may have an open hole in the block where a dipstick would go

 

[hugh g]

Is there a drain plug on that oil pan that may be leaking? My 3.0 had one. I never used it, too hard to see let alone get to.

 

[doubletrouble]

Rear seal of intake manifold, or valve covers?

 

[took-the-red-pill]

Hi all,

I placed 4 aluminum cooking pans in the engine bay. After 5-6 minutes at 2800 RPM the REAR DRIVER'S side pan was filling up.

So I made "cupcakes" from tin foil, and put them in my tinfoil pan, then placed paper towel in each cupcake so I could localize the leak within about 4 square inches. Then I placed it back in that driver's rear location.

The leak appears to be coming down the driver's side cowl near where the starter is attached. See photo. There is also oil on the starter and its wires, so I think it's coming from above that point.

ALSO: there is a large volume of steam coming out of the exhaust with muffs on. I don't think it's the water pump. The engine temp has been normal for 10 years, and is currently happy and steady at 155 or so, whether in the water or using muffs.

ALSO: there is a large volume of oil in the water that is exiting the engine. It's NOT coming out the plug, and any new oil inside the engine bay has now been trapped by the KR1000 Cupcake system. It's actually mixed with the water that has been through the motor and is coming out around the leg.

Could all three issues be explained by a head gasket issue?

Before any, "what about...?" suggestions, read this:

- Rear main seal and pan gasket was done by mechanic 20 hours ago.
- the following are either clean, too far away, or both: dipstick tube - top and bottom, fuel pump(they can leak oil), overflow coming from fuel pump, oil pressure sensor is on the other side of the motor.
- It ONLY leaks at higher RPM, when the oil pressure rises, so it's not valve cover gaskets. Also the plugs and area beneath them are clean.

- The photo: each 'cupcake' is about 2" X 2" with paper towel in them. The 2 horizonal lines represent the line where the starter meets the motor. The vertical line represents the centre of the boat. Obviously the black stains are cupcakes that saw a lot of oil in the 5 minutes while running it. The three below that which are brown seem to have had fresh oil dripped in them, not the blackened stuff.

Thoughts?

 

[took-the-red-pill]

Oh God could it be a cracked block?!?!

 

[Lou C]

Can you get around the back side of the motor and see if its the sealer on back side of the intake manifold, behind the distributor, maybe there was not enough sealer on that side and it is running down behind the end of the valve cover down to the starter. The front and rear of the intake manifold is sealed to the "china wall" of the block with sealer, not a gasket. Not sure though if that area is under enough pressure to push oil out. You can see what I'm talking about in this pic, see the flat surface right behind the hole where the distributor would go with a paper towel stuffed in it? This is from when I had to replace my old cyl heads.

 

[took-the-red-pill]

HI Lou,

Thanks for the idea. Mechanic had found a point where the intake manifold wasn't completely sealed along that China wall and fixed that up. But I'll check again. Can't hurt.

Cheers
Keith