Got my engine oil analysis back and it is showing considerable fuel loading in the oil. It has been suggested to run hotter to better burn off the fuel in the engine, but combustin efficiencies are showing quite well in other areas of the analysis. Excess fuel in the oil creates issues with degradation of the base oil. The gage on the helm reads a constant 170 once the engine is warmed up. This oil was run one season, or about 40 hours.

What do you guys read?

Should I run a 185 degree thermostat?

I think this is welcome to the open-loop rich system.

Solution: By an engine with a CAT (or a downstream O2 sensor) so you have a closed-loop system.

D

No cat for me!

170 sounds pretty average for the boat engines i've been around. I think I would worry about hot spots with higher temps. The engine's going to be "loaded" so it's going to be producing lots of heat. I think I rather have cooler water getting the heat out of the engine as efficiently as possible than warmer water to reduce the small amount of fuel in the oil. I think you're running a known and calculable risk now. That my change if you bump the temp. You're going to stress the engine one way or the other.

Change to 185, and run a hotter set of plugs if you are real worried about it. I would do nothing myself. The results are not serious enough to be worried about IMO.

Our boat runs at 185.

D-Rod is exactly right. Since until this year all marine fuel injection systems had no O2 sensors, they are run in an open loop. Well, a rich running engine is better than a lean running engine, as far as the manufacturers are concerned. So they set them up to run rich.
Your 170 degrees (which means you probably have a 160 degree thermostat) is about as hot as any marine engines with raw water cooling are running. Can you imagine how bad it could be if you had a 120 or a 140 degree stat like all boats used to get?
Plain and simple, the computer can't make enough changes to solve your "issue" no matter what thermostat you install. Just not enough sensors and input to the ECM. Sorry.

Thanks for the fast feedback. That's why I like this site... active! I've never changed the thermostat and I guess Mercruiser thought that was the right temperature to set it at. I just don't like having so much fuel in the oil... Suppose I'll not try to run the oil out like I do in my truck as optimizing a boat engine is not as easy?

I always thought this was one of the contributing reasons to change oil yearly no matter the hours of usage.

Merc and Volvo have to be pretty generic on what they program the ECM for. There may be aftermarket tuning maps or tuners or patches that can be applied to the ECM that better match the engine's requirements. Aftermarket ECM tuning is widely available in the automotive performance world, not sure about Marine.

If it runs good like it is then probably best to stick with OEM on all settings and change oil more often.

I'd leave it be.

"quite well" translates to "it ain't broke, don't fix it!"

Thanks FR. You put in terms I can understand.

What he wrote

The problem as I see it, deepv, is the oil analysis is giving you too much to worry about.

(sorry, I could not resist the humor)

Or maybe its closer to a Nyuk, Nyuk, Nyuk (in my best Curly Stooges voice).

Or, in the words of my admiral, "leave well enough alone"......

BTW, my boat runs ~175......