I need some help with this one. I just put my motor in my boat and i installed the crossover system that was on the old motor. The old motor ran at about 180 deg. but when I pulled the thermostat housing off to use it on the new motor I found that the thermostat was stuck closed?
So i put a new 165 in the new motor and now when I ran the new motor I get no temp or 120 deg. max. cant get ant temp in the motor and the oil temp is staying way to cold. Getting milk in the oil. Now I have tried putting back the old stuck thermostat and still no temp. Cant run the
motor like this any ideas how to get the water temp up. It has a bypass system. How does a stuck closed thermostat still allow the motor to run cold????

This would my concern " Getting milk in the oil."

How do you know the thermostat is "stuck"? Are you taking it out and boiling it in water to see if its opening?

What kind of crossover setup and how is it plumbed? 180* is a bit hot for my liking on a typical carb'ed marine engine, but.......what engine are we talking about?

you are not going to get enough condensation in crankcase to milk up oil in this short a time. you have a bigger problem than engine temp issues. find the leak. first culprit, intake manifold gaskets. second culprit, head gaskets or the heads themselves. you say your motor and your old motor. what is the new motor? somebody else's old motor? were the heads run in salt or brackish water for any length of time? are they mk4 heads on a gen 5 block? how old are exhausts, though they usually hydrolock engine, not water the crankcase.

Here is some more info, I own a boat that I built a 600 ci big block that made 720 hp ran it for 2 seasons no problems.This motor had a reg. circulating pump. Then I bought a 29 fountain that had a stock 502 that I wanted to swap motors and sell the other boat with a stock motor. During the winter I rebuilt the 600 ci motor changing the cam, intake, and heads ( the heads were run on this motor so I know they bolt up and no leaks. ) The headers are dry. So now when I put the 600ci motor in the fountain I used the crossover set up that I took off the fountains stock 502 that was running with no problems and that motor was running at 150 water temps.

Sorry but for some reason it did not post the whole post. Now I cant get the 600ci motor over 110 deg. the oil temp does not even move. Today I changed the oil and bypassed the oil cooler ( which I presure tested ) now the engine temp is still 110 but the oil temp came up to 140 still not hot enough but better, the milk is a lot less and the oil level never rises. If it was leaking water into the motor the oil level woud be rising. Also the motor was run on a dyno, warmed up cooled down gone over and warmed up a few pulls and let cool down no milk ran great. Dont understand how a motor can run so cold with a stuck thermostat, I put one in just to see and still no heat.

Randy are you sure the motor is not getting hot. With some of these cheap bypass setups the inlet water can bypass the motor and go right into the exhaust. May want to verify temp with gun or run it and place your hand all over the cylinder head especially front and back if it is really no temp the head will feel cool to the touch.

BB I have been checking the motor after a run and the block and heads are ice cold. After I shut it down I see the temp gauge go up from the heat soak but as soon as I start it the temp drops right down to about 120. Driving me nuts.

Could you be running in a lot colder water than you usually do or did ?

Crossovers, even with t-stats, in my area usually still run too cold both engine and oil for a part of the year. Work okay when lake warms up.

This sounds like the situation.