Hi guys totally new to this stuff but I understand the logistics of it all. So I bought this boat last year ran it a few times and noticed I had milked the oil, twice.. So I pulled it out tore it down, had block and heads machined put new bearings in it, new intake.had it all Maged and pressure tested. So yesterday was the first time I took it out since the rebuild everything seemed fine til the last part of the day when I pulled the breather on valve cover and noticed a bunch of white muck on the rocker,underside of valve cover, and breather. So I pulled dipstick and there was a slight sign of milk on there. It does however have a slight gas smell, I'm thinking I have the floats set to high. I also noticed that I have a decent amount of blow by and its puking out of breather a little bit. My question is what is going on here? No misfire runs great. Do I have too much oil? I have a stock pan and I put 8.5 quarts in it. I got the temp up to 150 cruising with 50-70 oil psi. I am getting very frustrated at this point because I just rebuilt and same thing occurs. Hopefully someone here can help  Holley750dp,stock454'oval port heads,

What kind or exhaust are you running best to post pictures of what your running and how you have it plumbed up a lot of times with boats it the exhaust that puts water in the oil


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It could be 5 depending on what it came from. I think the car pans were 5 and the trucks were 7.
My ford 460 had a 5 quart on it which I always thought was small for a jet boat.


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Does all of your exit water run through the exhaust? Possibility - When you shut off, water in the exhaust can get in open exhaust valves working its way into the oil. I've experienced this. Change the oil & filter again. You'll be fine with your rebuild. Must find your milking issue.

8.5 quarts in a stock pan seems off, you'll have to figure out what you have. If you had someone do the rebuild, they should know the capacity.

I don't like the ball valve being half closed. I run mine wide open.

Would like a pic from lower showing how the water lines are connected to the headers.

And you f I run the valve wide open, how will the motor get any temp? I thought that you wanted to run about 180 or so at idle. Like I said I don't know much about these boats I come from dirt car racing.

Yes that is correct All water goes out through exhaust.... Am I missing something? Should there be some sort of bypass or something of that nature. I know a lot of it needs to travel through the headers to cool them and cool the rubber couplings on exhaust.

Am I reading that correctly? ALL the water exits through the exhaust? No line out the transom?

Those hoses to the headers are weird looking not to mention big looking.


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I think its because they are water JACKETED not water INJECTED, like Bassets for example. Which is why I don't think his water is getting in through the exhaust. shouldn't be any water in the actual exhaust pipe, just in the jacket area around it (a pipe within a pipe)

Yes shocker that's where I'm at with the headers..... There should be no way water would come back through.  And it's normal to have condensation under valve cover right?

Some people say a little bit is but...... the only boat I've ever had that did that was my first boat with an Olds and that damn thing CONSTANTLY got water in the oil for various reasons.  Maybe your temp is too cool??

That's what my buddy was sayin... Who races these things all the time, he said I should let it get to 200 at idle and possibly it will evaporate. He also said he sees it all the time with these boats. I don't know what to do I will drain some oil out because it's obviously overfilled, and bring up the temp a little more next time and see what happens.

Sounds like a good place to start

I think its because they are water JACKETED not water INJECTED, like Bassets for example. Which is why I don't think his water is getting in through the exhaust. shouldn't be any water in the actual exhaust pipe, just in the jacket area around it (a pipe within a pipe)

Stupid double post


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Haha I appreciate all of the replies.. "The wonderful world of boating" he says...  I'm still wondering how it's getting in there. I can take a few pictures tomorrow of the dip stick and try to get one of inside valve cover. I can't really recall, but I wanna say I didn't notice this issue until I started closing the ball valve off to get temp higher. Which would potentially open a crack somewhere and let more water in. Not sure. Might be a dumb question but anyone every tried to get some block sealer in their somehow?

Can you post a picture of the jacketed header where it meets the rubber hose and then post a picture of your transom where the exhaust exits?

Jacketed headers on a jet can be a pain in the ass and most times need to exit the transom slightly above the water line. If the exhaust is submerged below the water line and at an idle the exhaust itself can flood quickly with water introducing a large amount of moisture where it doesn't belong. There is so much water introduced into the exhaust on jacketed headers to keep them cool to the touch that ideally you want the water to be introduced to the exhaust stream as close to the transom as possible. This is why many people will have folks like IMCO or Teague run jacketed pipe from the end of the collector all the way to the transom and only introducing the water that's cooling the header back into the exhaust stream at the very farthest point from the motor.

Yes, you want to run the line of raw water coming into the system wide open for maximum cooling effect. To counter the issue of too much water I run a pressure relief for the overboard between the pump and motor. This isn't a system that guys like GT are fond of but on a jacketed setup it helps to counter any reversion issues on jet boats when running jacketed headers but still trying to maximize the cooling effect on the header.

I run jacketed headers with an aggressive cam (.740) and it was a must when being rigged that the exhaust exited just above the water line at idle otherwise milky oil would be an issue. Putting a modern style jacketed header on a boat that utilized the older log style headers isn't always a plug-n-play type scenario.

I'd pull off each exhaust and check the manifold flange where it meets each cylinder for any signs of water reversion such as rust around the head or header. It wouldn't hurt to have the headers pressure checked as well. If those headers are cheaper type jacketed they probably have a steel inner pipe rather than stainless and can be prone to rusting through if the header isn't drained routinely.

I've had my share of challenges with jacketed headers on a jet boat. It's all a pretty basic system but you need to learn their nuances to set them up properly. Your problem is likely something very easy so I'd start at the basics first.

Ok rvrrts below is the pictures.. One thing I don't understand is.... If it's getting reversion through the headers how the hell does it get in the crankcase without misifire or hydrolock? Is it just pushing past the rings? And yes the exhaust exits below water line.