omc Stringer Over heating

First off the engine is a 4.3L V6 that the previous owner got from a gm vehicle.

The problem is the temp gauge is all over the place. Not sure if I'm really overheating or not. engine feels like it gets pretty hot to touch not scalding but hot. The guage reads about 155 when the engine is idling but when I start cruising at full speed the temp gauge shoots right up to like 200+ when I back off the throtle it cools down to 160 within 30 seconds. Does that seem right?? Not sure if the temp sending unit is off from a vehcile, Is there a difference? I changed the impelor and the thermostat. Another thing is when I run without a thermostat the engine staya cool but manifolds get really hot. So I was thinking the engine block is not cloged. one of the manifolds has a small leak but I don't think that would cause it. Anyone have any advise do you think it could be a water circ pump on the engine?
Thanks.

Re: omc Stringer Over heating

The only way to really know is to get an IR thermometer and shoot it at the block and watch for the actual temp.

On muffs you should see water comming out at the back of the boat that would be an indication of how your water is circulating, you could also feel the temp of that water as it should feel warm not scolding hot.

It could be a bad sender, bad / wrong thermostat. MARINE stat not auto stat.

Bad gauge. An IR therm will tell you the true story. just saw my machanic do this yesterday and after replacing impellor and t. stat, after reading block temp all was good. Gauge however still read a bit on the hot side so he feels sender is junk. ( NOT my boat )

Start there.

Re: omc Stringer Over heating

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