How and is it important to run a thermostat? My boat is a 79' Scarab 300 with twin 330 hp bbc and TRS drives, I pull water in from the bottom of the boat, I guess it is considered an open system. I pulled the t stat housings off, the port engine had a stat, the starboard didn't, never heard of doing that, I've only owned the boat a couple years changing exhaust on the boat putting captains call on it trying to get it out of the
70's

I don't have any stats. I always do make sure though that I get the oil temp up enough to boil off any water.

the problem with no t-stat. your block is too cool. it is designed to run at a certain temp. you will get rapid bore wear from too low an operating temp.

as well as poor fuel economy and condensation.

Run the thermostats. They are there for a reason.

OK, what temp do you need to run or do they only have one temp?

Guys around here been running big power supercharged big blocks in boats for many years without water thermostats. The reason for it is a cool block and heads means less chance of detonating.

However, in a 330HP 454, there really isnt a reason not to run stats. If you dont have oil thermostats, then put the water thermostats in. 140* stat is fine.

I think efi and mpi's run at 160...

I doubt his 1979 30ft scarab with 330's has MPI or any kind of EFI. The OE merc stat for his engine is probably a 143* merc unit.

just q carbs no efi thanks guys. I have another ? I changed from the old log style exhaust manifolds to center rise, my thermostat housing is 2 parts, lower has outlet to the water pump (circulating pump) outlet to sea water pump 4 outlets to exhaust/riser, upper has 2 outlets to exhaust/riser.With center rise I only need 4 total. Is there a upper without outlets and still be able to run stat?