Engine runs colder than I thought

TADTOOMUCH · Post by **TADTOOMUCH** » Tue Mar 17, 2009 7:26 am

After looking at a previous post about low oil pressure, I got to wondering about my F-32 and the water temp reading lower than what I thought it would.

I run in Lake Michigan and the warmest I can get the engine to run is about 130 to 135. I have new gauges, sending units, and thermostats.

When I winterize the engines I can get it up to 160 for a while with the antifreeze solution recirculating through the system.

I thought that after she warmed up under cruise, that she would run closer to 160 once the thermostat opened up but, she runs no warmer than about 130 or so.

Is this normal?

Oil pressure is stable and within specs at prescribed rpms.

Everything else seems fine and the water pump works well and manifolds are all in the same temp range when running.

I've checked with some others in my marina and their boats run closer to 160 but are not Trojans.

What do you guys think?

Paul · Post by **Paul** » Tue Mar 17, 2009 8:08 am

Sounds normal to me for an open cooling system. My 350 Mercruiser also has a 140Â°F thermostat and runs in the 135Â°F to 140Â° range. A closed cooling system with a heat exchanger would normally run hotter with a thermostat rating from 160Â° to 180Â°.

If you have an open system and find that your engine(s) run much hotter than the thermostat (160Â° with a 140Â° thermostat) this usually indicates some type of problem such as a restriction, blockage or lack of water supply.

Hope this helps.

gjrylands · Post by **gjrylands** » Tue Mar 17, 2009 8:45 am

I also run in Lake Michigan with raw water cooled engines. Like yours my engine temperature is 130. This is normal and my engines run great.

Closed systems run hotter.

jddens · Post by **jddens** » Tue Mar 17, 2009 11:20 am

My F30 with 350 merc's and closed loop with heat exchanger run at 160.......about right for closed loop...........

prowlersfish · Post by **prowlersfish** » Tue Mar 17, 2009 7:02 pm

Your fine

LandVF36 · Post by **LandVF36** » Tue Mar 17, 2009 10:45 pm

Our F36 with open system cooling of twin 454s runs about 130-140 as well. We're on the Mississippi south of Minneapolis where the river water temp ranges from the 50s in the spring, near 80 in August and back to 50s by the time we pull her for winter storage.

rossjo · Post by **rossjo** » Wed Mar 18, 2009 11:44 am

Might want to check with an InfraRed temp gun - you can get a hobby model for about $50 - and know exactly what your temps are ...

Paul · Post by **Paul** » Wed Mar 18, 2009 12:41 pm

Captain Ross's suggestion is a good way to check your entire system from the pump to the mufflers. Keep in mind that if you ckeck it with an infrared thermometer that external engine temperatures are always a few degrees cooler than your actual coolant temperature. This is due to heat dissipation on the surface of the castings. The best place to verify what the gauge is reading is just below the thermostat.