New 502 with 500efi cam hit the water this weekend. Engine is running very cool 100-120 on the throttle. Gauge will hit 160 then right back down to 120 when I idel her down.. Running 160 Tstatt. Removed housing today and its not stuck open.. whats the problem??????

Need to make sure you have the correct thermostat. Should be a 140 degree and need to make sure its one from the marina for an open cooling system if its not a closed system. It cant be a thermostat from the auto parts store those are for closed cooling systems and plus the ones from the marina are stainless steel to prevent rusting. This is what I have found to be the problem in most cases like this. Just my 2 cents.

I have the same setup for a motor, but mine has a 160 degree thermostat in it..................

502 mpi uses 160* stat .... 502 carb motor 140* Stat .....m

yes I am running an 160 automotive T-stat. Is a marine T-stat really different?

no.......

If your saying the motor runs cool at idle but runs warm at speed you have a restriction issue or a bad impeller ...if your saying its running about 160-170 at speed and this is a MPI motor all is well ......m

running cool most of the time.