Already have a complete setup, so what is the easiest way to ad a thermostat? Looking for the least additional plumbing.

You may want to consider a closed cooling system instead. I have noticed that you can get good oil temp at idle with a closed system running above 165 F. You also get all of the added benefits of closed cooling.
Steve

Not sure of your setup, but if you just want to rig an oil thermostat into your existing system, this old picture shows an install that is about as easy as you can get. IMO, it is best to do this project with the engine out of the boat. Remember, an oil thermosat slows/controls the flow oil so generally you will need to upgrade your existing cooler so you can hold the oil temp in the 212-220 degree range....even at extended WOT runs.

Forgot to tell you guys that I'm running dual cooler bellhousings for my engine oil...

http://www.holley.com/types/Sandwich...hermostats.asp


Jeff

The Mercury HP500 style thermostat/filter mount is one of the easiest to plumb and mount, the only drawback is that the fittings are smaller than some of the aftermarket units... IMO.

The Eickert/Hardin unit is a nice piece, but they tend to be a pain in the a$$ to plumb and mount due to their shape:

http://www.cpperformance.com/p-14580...12-degree.aspx

Canton makes a nice piece too, and it's easier to mount and plumb:

https://www.cantonracingproducts.com...ion&key=22-480

i installed the Canton thermostat last fall. Was pretty easy. I had to modify a few lines, but nothing major.

works pretty well, and got rid of 95% of my condensation problems.

i like the idea of a sandwich adapter but my motors are gen 6, and i dont know if anyone make a thermostatic unit for that motor

Whatever you use, it'll more than likely have to be remote mount. So, it's not going to matter what gen engine you've got.

The easiest to use would be an oil cooler with the oil thermostat integrated. Dont have to change/add any oil lines. Little more expensive but probably much less of a headache.

http://www.cpperformance.com/p-13666...il-cooler.aspx

Now with that said, I have the Canton and it seems to work very well at keeping the oil temps up, even with no water temps.