oil leak on new rebuild
 

I have been chasing an oil leak on one motor since I rebuilt them back in Aug 22. I ran them on the ground for the cam break in. Changed the oil by draining the pan 2 times and then put them back in the boat. Finally got the boat completed and went for a ride. I noticed after a few hours oil and a little water in the bilge... Yuk! what a mess. The next day I came down and checked for signs of a leak. The Port engine was 1 quart low on oil. Starboard was ok. I reached way under the pan to the plug and found clean oil amber color on my hand and a little on the left side of the pan by the dipstick. I decided to change the pan plug with a new one and a new Mercruiser washer/gasket. After that waist of new oil and refilled the engine came back the next day and it seemed dry. After going for another ride I still found oil in the bilge but not as bad as my first ride. Came back the next day, checked the oil level and now it was 1/2 quart low with the same hour or so of running time. So I thought I was getting closer to my issue. As for the dipstick tube where it enters the pan I took rtv ultra black and sealed the tube. Last weekend looking at the right side of the engine back 2 bolts on the oil pan by flywheel cover were wet with oil. I now have 11 hrs of run time. I tried to tighten them a bit. The gasket I bought for the pan is the Hardin Marine 1 piece (guaranteed not to leak).. ?? I called the machine shop guy that rebuilt my engine. He said he put silicone on 4 corners of pan and then on the outside of the pan in the back after pan installation. I asked him about the rear main seal which were 2 piece Felpro's. He doubts it was a rear main seal leak. I don't see anything wet or dripping near the bell housing. He said I would only have a teaspoon of oil. I read that you would loose a lot of oil in a short period of time.. I then tried to reach further under the pan and felt oil between the back of the oil pan and the flywheel shield cover. wow...Maybe the pan gasket is leaking when the boat is getting on plane and all oil rushes back in the pan? I never had oil leaks...like this on a new rebuild. I decide to put dye in and see. Well it is definitely coming out by the top pan bolts. My engine builder wants to do a pressure crankcase test and see with soap bubbles where the leak is.. The boat runs so awesome and now I have to pull the engine out again. Maybe i will put dye in the other one to make sure.
Any input would be appreciated. Thanks in advance.

That's a lot of oil to lose in a short time. Are you sure it's not a valve cover or the intake? It can be really hard to see especially at the back of the engine. Or maybe a sensor or oil line/adaptor?

Take a close look at the oil filter relocation block at the engine. That was my leak after 700 plus hours on the engine.

Thanks for your suggestion but it's definitely not the valve covers or the intake I can get to the back of them with no problem.

I checked the remote oil filter block with the 2 hoses which go to the oil cooler and filter. The hoses and everything else is dry.



. I also remember changing both seals on the remote oil filter block.

Rear main?

I'd look hard at the valve cover on that side. With the exhaust in the way a leak would be near impossible to see with out being a contortionist. Use mirrors or what ever to look up in there.

Why can't it be, just once, something easy and inexpensive.

As you can see I have plenty of room in back of the valve covers. It doesn't leak when idling first start up of the day. It starts to leak when getting up on plane or at high rpms and when the oil is hot. I will check again this weekend. Last boat ride.
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If the back of the oil pan had a leak. The part of the pan that sits on the bearing cap. While getting on plane the boat is at 45 degree angle. Doesn't the oil all migrate to the back of the pan at that angle. It maybe just dripping out. I haven't seen any spray of oil anywhere. If it was the rear main seal the bell housing would be wet inside and the flywheel shield behind the flywheel would be dripping oil. I have gone through 2-3 quarts in 12 hrs. Possibly the starter wet also. Left hand rotation.