Swapped thermostat and still.

You said you went through the cooling system so you back flushed all the hoses and stuck your finger in the end of the oil cooler and felt around for debris? As mentioned above, you should get enough hose to swap pickups between the engines at the transom. Did they rebuild the one engine or both?

I have still not found the problem.

i have gone with a heat gun during a run.

When I put the heat gun on the thermostat housing prior to the thermostat I’m getting 195. After the thermostat around 160.

i have changed strainers, hoses, and gone through the whole cooling system.

would anyone recommend where I look next?

thanks

Post some Pictures front , back, sides and tops of your engine . I would think it has an oil cooler. Replacing it would be a good place to start.

Chris

I’ve cleaned it out. I do not believe that is the problem

There were others back in 2010 with the same problem here on oso. "Merc 1075 Overheating"

Yes I went through all those topics but I’ve done everything that they recommended in them. I am yet to find the culprit

Did you switch the pick-ups with longer hose?

What are the guages reading for temps?

When you follow the raw water path from inlet to outlet...does the temp/flow change from the good engine?

You sure you are overheating and it’s not just a bad guage or sensor?

I had a friend with a similiar problem on a 500EFI.
Chased the problem forever , turned out the salty, rusted block and cooling passages were blocked.
You got it from Miami,it`s probably salty . Is the "reputable" builder Randy from Cobra?