Working on my 89 260 stinger with stock 5.7 and was wandering if the engines should have a thermastate in them or not. Any ideas?

Yes the engines do need a T stat. they need to run a minimum temp to operate properly. If the engine is too cold and you beat on it you could do a lot of damage.

No engine should run without a thermostat. All engines which produce horsepower need to operate at "operating temperature" for optimum performance.
In a boat the steady flow of water will cause the engine to run cooler than normal which may cause loss of power, sludged oil or fouled plugs and a host of other conditions.
In an automobile with a radiator, if an engine operates without a thermostat it might even overheat! you ask how...it's because the coolant does not stay in the radiator long enought for ambient air to cool it so you are sending hot water back into the block. In a boat you are probably using sea water which is already cool causing lower than normal engine temps.
Hope that helps you inquirey?

I run a restictor plate in mine...

where can i get a restictor plate? so i dont have to keep worrying about a thermostate?

i want it to run around 160.

160 is too cold if you ask me???????????

I would run 182-185 for optimum performance.

Moroso makes the spacers. You can get them at Jegs or Summit.

I think 180 is a little warm especially running a hotter setup where the higher temps could increase the chance of detonation.

If your engines are stock, why not just run the thermostats recommended for it? You can get a 140 degree thermostat from West Marine pretty cheap.

thermostats can stick, especially when boating in muddy,sandy areas. the grit can get stuck in between. just seams simpeler if there is nothing to go wrong there.

I've never had that problem.

The mud and grit you plan to run in will eat the water pump impeller in the lower unit of the alpha one drive before the T stat gets pluged. Best to run the stock setup and stay out of mud. Mercury spent a lot of time to come up with a system that has worked very well for a long time. Even if they didn,t invent it. It works.