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......

Yeah, yeah, yeah. It has permitted me to run my truck out a lot longer and discovered things going on with my engine. Maybe it isn't worth it as much with the boat.

Almost forgot, the houseboat thermostats are 140°, pretty chilly. Probably got plenty of bad things in those oil pans...Just checked a pic of my babyliner's dash, gauge is just a tic above 175. They do seem to be running the newer engines a lot warmer than the old ones.

My engine idles arround 170 to 180*.

Runs 135-140 flat out (no thermostat in the system).

Sounds like a problem of accumulation from running rich all the time.

DeepV,

What brand and weight of oil were you running ???

What was the fuel dilution percentage ???

My 20 year old OMC raw water cooled with a 160 stat runs right at 160. With raw water cooling you don't want to go much hotter than that, keep in mind a raw water system it not pressurized like closed cooling. That means you can have localized hot spots even though the engine may not be reading overheating on the gauge. With closed cooling you can go hotter, just like a car system because the pressure cap has the effect of raising the boiling point of the coolant.

As far as fuel dilution, I'd check the color of the spark plug insulators, are they black, if so the mixture could be too rich. But always better to err on the side of rich vs lean for a marine engine that runs at 3/4 of max power most of the time. So you may well wind up leaving well enough alone!

Deep, "higher" fuel dilition percentages are perfectly normal on a marine engine. I'm also curious as to how bad the UOA was. How did the TBN fare against the dilution?

For comparison,my 2 UOAs showed 1.5% fuel/ 335 flashpoint after 108 hrs and .5% fuel/ 375 flashpoint after 75 hrs.

Mine idles at 170° and at normal running speeds climbs to 180°

You are suffering from paralysis by analysis.

Change the oil every 50 hours or so and have a great time boating!

I was running Valvoline extreme blue 15W40.

Fuel dilution 1.64%

TBN 3.9

TAN 2.27

This oil held up better than the Merc 25W40 from last year's analysis, but exhibited a higher percentage of fuel dilution.

"paralysis by analysis"

I've heard that before in just the form "analysis paralysis"!

3.9 TBN...lots of "cushion" still there Deep.
Did you pull the 2 samples under the same conditions?
Any chance you might need a cleaning dose of a Sea-Foam type cleaner, or do you run the FP3000 in the boat also?

The TBN was good but the iron was getting up there.
Last year it was in March and was sent in pretty quick. This year I sampled in January but the sample sat in the bottle for 2 months.
No additives used but I am going to be using FP3000 and some Bio Valve Lube from Renewable Lube.

My bad. By "same conditions" I meant were both samples pulled say after the same warm-up time, or is it possible the results got skewed by something along those lines..samples taken after differnt running conditions..???

The factories run our motors rich and cool to keep 'em living with the loads and RPMs they have to put up with. I'll bet a UOA of ANY "stock" marine motor would show fuel dilution that would be cause for concern in a road vehicle...the nature of the beast so to speak.
I think the key is to keep good, high quality oil in her, and be diligent in keeping the fuel and ignition systems as good as you can.

The first sample was pulled after running the engine on the muffs until it got to 170 each time and through the drain hose out the garboard drain hole with the first quart or so going into the pan.

The second was done at a local Mercruiser mechanic's shop using a suction pump through the fill tube after they ran it on the muffs to get it up to temperature.

Deep, to me, the way the samples were taken doesn't seem like it should have changed the dilution numbers any.

Some things off the top of my head that you can check/do that could affect fuel dilution:

Clean flame arrestor
Replace plugs, cap, rotor
Clean pcv valve
Replace fuel filter
Run a heavy dose of cleaner thru the fuel system/ ensure good injector pattern
Check compression and leakdown
Check ignition timing
Check resistances/ functions of the various senders for the ECM either manually or let a dealer tech use the Merc scan tool...especially the temp sender