I have a BB 502 HP and for the last couple of seasons I have not run a t-stat. My temp guage never really moved,as I would think is normal with no stat in the motor. On the 4th of July,my boat started reading between 130 and 140 degrees. No I know that's not too hot,but I still don't have a t-stat in the motor. This makes me think if I had a stat I would most likely be running too hot,and I have a water pressure or temp problem happening now....Any ideas????? Oh,and I also lost about 2-3 mph on GPS?????

Why dont you run a stat? Usually only supercharged engine guys do that. With the engine running hotter you should have produced more HP. If the pump impeller is going bad than the engine would not get as much water as before and would run hotter. But this would also mean that you would have less water going out the exhaust and unless you were already running lean it too would increase HP. If you were already running slightly lean than the reduced water flow would cause the engine to run quite lean and this would cause you to lose HP.

Thank's T,B....The real reason I don't run a stat is quite honestly,I pulled it out to winterize it,and never put it back in. Funny,but yesterday I was trying a drive out,and the port side of my transome was filthy. Starboard side,clean as a whistle..Usually,my transome is always clean

Running stock Merc. circk. pump: Crossover: Crossover with bypass: ??? We don't have enough info here to give you intelligent advice! --- Jer

Check your raw water pump?(impeller). You should really have some heat in the engine. You said before the needle never moved? You're running a cold engine and cold engines require more fuel. A freind of mine has had problems with his 406 bogging or popping through the carb. I didn't realize it but he had a 120 thermostat. After a season and a have of messing with the carb,jets,accel pump,squirters,timing, whatever ,I told him to change to at least a 140...now it's ok. Could probably pull some jet out though.
But I would start by checking the pump.

I am with JP on we need more INFO. 502 carb or EFI motor. Type of cooling system.