Hey Yall,

I just ran my boat all day, when pulling in tonight I found some oil on the transom, on both sides. I assume this came out of the breathers on my valve covers. Upon further exam it appears that my oil has become a bit milky.. I have had some issues with water coming through my over the transom bassett headers so I m hoping that if I change the bassett tee valve(  cause its old) and do an oil change I will be good to go. Its a 455 OLDS and I didnt feel any power loss. Everything else feels and looks tight. Any help is greatly appreciated !!!

Thank you for the response. I have a pressure relief, it's brand new (not to say it can't be locked up) I was having pressure issues, but that has since been addressed. and stays around 10 psi now. I hate to start pulling everything apart but that may be the road I'm heading down. Has anyone else had issues with the Bassett tee valve and could that be a cause? Are there any other things I need to do other than drain all the oil and change the filters?? Thanks again for any help.

If it's not from over watering the headers at low speed, I'd be right back looking at the intake manifold. You'll have to pull it off, clean everything up immaculately, and re-assemble with quality gaskets and a good sealer like Ultra Black (my personal favorite). My old 455 was a bit of a problem child in terms of sealing the corners of the intake.
Also, when you put it back on, omit the rubber/cork end seals and just lay down a nice bead of silicone, approx. 1/4" diameter.

You have Bassett headers each header pipe has a small hole in it right at the lowest point of the pipe.  Do drain and water on the headers.


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Thanks for the reply, I have made sure that those weep holes are clear when I'm idling I do get a little water blowing out those weep holes.

When you say “water coming thru my headers” are you talking about raw water coming out of the end of the collector at idle. If so, that is too much.
Have you taken the tee valve apart? There is a ball and spring in there. They can stick or the spring can break allowing too much water to go into your headers.

When I first got my boat, I was getting water in my oil. I backed off the ball valve on my jet inlet and haven’t had an issue since. So yes, inlet pressure from the jet can be an issue. But you do have a bypass system so just make sure it is working correctly.
Do you have good flow coming out of the dump line (where the cooling water line exits the hull)?


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Thanks for the reply. I changed the valve to a gate valve off the pump. From the closed position its only open about a turn and 1/2. I think I'll also try closing that a little more and raise the engine temp. My gauge is roughly 130 when running so maybe still getting to much water.

Silicone work really good, don’t use the gasket that go on the front and back. Also use silicone around the water ports front and back of the intake manifold. Don’t mess with the silicone for 24 hours. Are you using the metal intake manifold? If so get high performance gaskets. Still use the silicone front and back and around the water  passages even spray the gaskets with an  adhesive. Some times if the block has been surfaced the manifold doesn’t fit right in the block. Good luck


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I had the same problem end of last year and beginning of this year. But it is now solved. So this is what i had done and my set up. My engine only had 55 hours on it and one day i check the oil and behold water in the oil. Did a compression test and all the cylinders were 160psi plus except one that was about 145. Did a leak down and it was coming thru the rings a little. So had the new intake gasket put on and same problem. Found a rebuilt heads C big valve and put those on with quality marine gaskets with another marine intake set and still same problem. Then i did some more research on the intake manifold edelbrock performer can warp on a jet boat due to the cooling cycle or whatever so i ordered a new manifold the rpm air gap and installed that did another compression test with the new heads and cylinders went up about 10psi. And I haven’t had a problem with water in the oil since.