Rivrrts if he does not have a big cam. Is reversion a common problem? The rise is going to be a bigger air gap than on a snail and log. Also how do people pressure test jacketed headers?
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Reversion is less common the smaller the cam. There are specs on most any header websites like Rewarder and Bassett giving examples of suggested cam sizes to lessen the chance of reversion. Of course there are ways around everything and lots of different ways to lessen the chance of reversion like introducing water at the transom and water exiting above the water line.
For lack of better terms they check the pressure no different than they would check a gas line. Cap the one end, pressurize the exhaust tube, put a gauge on it and watch to see for any line loss. Places like Lightning and Teague can all check them for you. I'd imagine a reputable exhaust company can do the same.
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.
It doesn't take much water to turn the oil to milk shake. I've seen milk shake from slight condensation under valve covers that burns off rather quickly and returns back to normal with no ill effects.
Water exiting below the water line, especially at idle or shutdown is not ideal. With no way to regulate the system it's not hard to imagine how easily water can become a reversion issue.
Most reversion occurs at shutdown. You'd know how serious the problem was if you had a hydraulic issue but when there is just enough to end up in the pan I'd say it's most likely happening at shutdown, becoming steam, pooling on the piston, and finding itself in the pan. This scenario would explain why you're not experiencing any misfire. Just enough to milkshake the oil.
If you can eliminate the cause being a leaking jacketed header or typical reversion then I'd pull the intake manifold and take a look. You may have an intake gasket issue and water is leaking into the oil valley and down into the pan.
I'm no professional on this deal. Plenty of people on this forum with way more knowledge on the issue than I have but these are the most common places to check in my experiences. Also the easiest for the DIY weekend warriors like ourselves to solve without paying labor to someone that you can easily do yourself.
I didn't read the entire thread but are you running an oil cooler? If so it's also another place water can find its way into the oil system.
The good news is that these boats are fairly basic and it's rarely an overly complicated issue to resolve. Only a few places water is entering the oil but will take checking a few common places and making one check at a time, confirm or deny the culprit, and then move on to the next possible location.
