I have a 502mag/mpi in my boat. I had it out last weekend for the first time since buying it and noticed 2 things about it. First it idles around 900rpm and water temp never rose above 100 degrees. I pulled the thermostat housing off to find no thermostat. I went to the dealer and got a new 140 degree thermostat. My question is with a thermostat when the engine reaches temp will the idle go down? I am thinking it has a high idle setting when the engine is first started and should idle down when it reaches operating temp. Dose this sound right??
Thanks!!

Stock Merc carb engines use a 142 degree thermostat. My 502 MPI
uses a 160 degree one. Running temps that are too cold are bad for
an MPI engine. You will run rich. This will mess with idle quality and
may foul your plugs. Change it.

+1 Needs a 160, that what merc puts in all mpi/efi to make them run right. I have 160's in both of mine but mine idle at 600