The bypass hose that runs from the circulating pump to the intake. Should it still be used when going from a merc intake to a merlin??
The Merlin doesn't have the fitting at the front of manifold like the stock.
Some pics would be nice.

Good point.I have Team G's on mine WITH a bypass. BUT...there is also a bypass in the T-stat housing. You could probably just plug the pump and do without it.

I'd use the steam port !!

Steam port ????

By-pass is there to circulate water and vent any air out while thermostat is closed. If you plug the by-pass I would drill 2 or 3 3/16" holes in thermostat to vent any air out before engine warms enough to open thermostat. No steam pockets. If you boat in a cold water area and drill holes you may have trouble getting heat up at idle. Never ran this set up with a water pump but I have with a cross over. Couldn't you add by-pass port to merlin intake? Or use a thermostat cover with a by-pass port for a circulating pump. I have seen them but none I liked. Sorry couldn't be of more help. There has to be some here that have been down this road before.

It will work fine if you drill afew small holes as said above or 99% of the time with out the holes
I plumb all my motors with water lines from the back of the intake cross over to the thermo housing with #4 hose to stop steam pockets in the rear cyl ,like the cup motors do it really helps head gaskets and cyl temps ,pm me I'll draw it out for you

Bobby, it seems that what you're saying is that drilling holes in the thermostat isn't really necessary, but it is okay if you do---right? Living up here in Michigan, the warmest the water gets up here in the dead of the summer is about 70*, but usually in the 55-65* temp range in Lake Michigan. I run 160* thermostats in my engines----what would you recommend as far as drilling holes in my thermostats----and how many if any with the info I have just given? Thanks

Mark/KAAMA

As far as the holes in the thermostat are concerned, we think that it would be good practice on most any system. Bear in mind that everyone uses automotive thermostats, which are designed to have the same temp (more or less) on both sides of the t-stat. Here at Stainless Marine, we drill 3 5/32" holes in the dome.