Thermostats

David Kane · Post by **David Kane** » Tue Oct 07, 2008 8:34 am

I'm running 140F thermostats on my Mercruiser 255's. They were in before I bought the boat. I'm wondering, since we don't run our boats over the winter in the northern clime, should I even bother having thermostats at all? I'm thinking they're just another thing that may go belly up & could be eliminated. When I lived in southern California, I didn't keep thermostats in my vehicles. If you do think I should run with thermostats, is 140F too low?

TADTOOMUCH · Post by **TADTOOMUCH** » Tue Oct 07, 2008 8:44 am

Yes you need the thermostats to help keep the engine running at the optimal temperature. If you don't have them, it will run cold all the time and the oil will never warm up and the flow rate of it will not be as much if you use a multi-viscosity oil. Also fuel economy will suffer as the carbs should be adjusted to warm running temps. The engine thermostat should keep the cooling water between 140 and 160 on most inboards.

Paul · Post by **Paul** » Tue Oct 07, 2008 12:16 pm

Fuel economy will also suffer without thermostats.

Stripermann2 · Post by **Stripermann2** » Tue Oct 07, 2008 2:19 pm

Yep...condensation in the oiling system, less than optimal engine performance and corrosion. Plus when not running a thermostat, accurate indication of engine temperature from your gauge will never be attained, thus possibly causing an overheat condition when it's too late!

Run a thermostat for sure.

David Kane · Post by **David Kane** » Wed Oct 08, 2008 9:43 am

Thanks for all the replies! Will get 2 thermostat/gasket sets today to do both engines. My supplier has 142 degree thermostats, so they are in the range.

MattSC · Post by **MattSC** » Wed Oct 08, 2008 7:08 pm

My original LM318 was raw water cooled, I ran it without the thermostat from 1994 until I repowered in 2003. At that time, my engine had a little over 1800hrs and never gave me one problem. When I did try to run the engine with a thermostat it would run too warm. I had new hoses, manifolds, elbows, and risers, plus a new raw water and engine circulating pump. I never had any problems without the thermostat and put on approximately 1100hrs that way. I did inspect and tear down my old engine out of curiosity The water passages in the engine block were restricted with crust and stuff which probably was the cause of my warm temperatures with the thermostat, the boat had been in salt water for 19yrs. Everything else looked good for its age with no abnormal wear, though the timing chain was a little stretched. If it were me and the boat ran fine with the thermostats I'd keep them in, I really didn't have much choice. The engine needs to be at its normal operating temperature to make its advertised HP, and will burn less fuel.