Running Cold

mbnarney

So I take the boat out and it comes up to temperature(140) I am in a no wake zone and after about 30 minutes I notice gauge has dropped to 100. Check the motor and its not running hot. Take it back to the dock another 30 minutes, still not running hot. I do the checks on the gauge and sender unit and all is well. Got an IR gun and ran it another 30 minutes and it never gets over 104 at the heads and about 90 at the sending unit. I am thinking thermostat but I am pretty green at this so thoughts? 

Dream_Inn

Yes, thermostat is definitely where I would start.  Sounds like it is stuck open.

mbnarney

That was my thought. Boats in the water. Is there any reason that it can't be changed while in the water. Or do I need to have it pulled?

Pat310

https://youtu.be/Lu7nr0QYWHs 
good video on changing thermostat on MerCruiser and yes can be done in water. 

mbnarney

@Pat310 perfect Thanks