V drive mercruiser 350 5.7 cooling issue*

Sorry for the long post.

The guy who i bought the boat from paid a guy to install a new motor. *The new motor has a chevy bowtie on the head area. *The boat came with a mercruiser 350 5.7 I believe but have no records. *I have tried to get the boat to run on the hose and at the lake. *Every time i run it no matter where, it overheats. *I have a infrared heat gun that i pointed at the exhaust elbows, when it overheats, those are running at around 210 and the guage is anywhere from 200 to 250. *When I shut the boat off i can hear water boiling near the thermostat. *I have anothe boat just like it the same v drive and basically the same engine however mine is a mercruiser with EFI. *My boat runs so cool that you can easily put your hand on the exhaust elbow after it has been pulling 5000lbs through the water for 6 hours. *You cant do that with this boat after 20 minutes of running it.

I have changed the impeller and verified that all the plumbing is correct to my seloc manual and matches my boat. *I have changed the thermostat out from the 180 that was in it to a 160 which is what the manual calls for. *I have taken off hoses to make sure i am getting plent of water coming out of the impeller. *Also the first time i took the boat to the lake, it ran smooth but overheated, althought it took a while for the boat to overheat, it got so hot that it actually blew off a hose. *Needless to say we paddled in. *After that experience the boat runs smooth but now smokes which it never did before. *Also I had another issue last night when testing that it appears the engine is now leaking water somewhere under the engine. *All the hoses appear to not be torn and i cannot find where the leak is coming from. *The manual said that there is a standard rotation and a non-standard rotation engines and you have to adjust the impeller for each... i have tried adjusting the impeller both ways with no sucess.*

Anyone have any ideas? *All the marinas around me are booked up until well after the 4th of july and ive come this far, i am wondering if there is something small I am missing or something big i am missing... haha *Here are my possibly thoughts of what it could be next:

- could it be a blown head gasket
- water pump on the engine is not the marine application or not running properly.
- something i am not doing properly with the cooling system.

I am trying to find a mechanic to look at it but in the mean time i would appreciate any help i can get.

Thanks!

is the engine pumping water out of the exhaust when you run it?

Also is the water pump a standard or reverse rotation?

Check your tranny cooler filter for blockage.

Does your impeller housing have grooves in the head plate?

Water is pumping out the exhaust but not that much water is coming out of the port exhaust.

Not sure if the water pump is standard or reverse. There is water getting to it though. I pulled the hose off that pumps too it.

Tranny cooler is not blocked. Pulled the hose off that to verify water can flow out.

Not sure about the water impeller housing. It's pumping water good and looks the exact same as my other boat. And was put together to spec from the manual.

I have been doing a little research. I think it's a blown head gasket. I'm going to try to find a way to test that and will see from there.

What does your oil look like? If it's a blown head gasket it'll look like chocolate milk.