Wee-Bit Oil Analysis Report

[JdaleH]

My Honda 90 engine oil is presently at 127 hours because we were cruising the Erie Canal and couldn't change oil while in the water. Because of the speed limits on the canal, we were only able to run at high speed for about seven hours up and back on one of the finger lakes at about the middle of our cruise.

As we have our boat up for sale, I obtained an oil analysis report that I added to my photos. All metals analyses were good. Fluid Dilution and Oil kinematic velocity were moderate. Let me further explain the latter as these results put me into research mode as to what is normal, moderate, or critical. I think my findings will be helpful to the community.

As the lab does not have enough data on outboards, the "moderate" fuel dilution is based on values between 1.5 and 3.5 percent dilution for all gasoline engine uses. The lab states that 3 to 7% can be acceptable as long as there is not a noticeable increase in wear or drop in lubricant viscosity. Because my wear metal report is good and the kinematic viscosity is just below the standard between 20wt and 30wt oil, I assume that 3.5 % dilution is high normal. As mentioned above, if I had changed oil a bit sooner, as I normally do at 100 hours, my results probably would have all been "normal" for an outboard.

As we should be aware, our Honda outboards have relatively higher fuel dilution because we run them at low rpms at displacement speeds. As a result, the oil temperature does not get hot enough to volatize fuel bypassing the rings in the oil. This is a normal and expected occurrence that is compensated for by the recommended Honda oil change interval and using TW-C oil.

If the fuel dilution is, say, less than 3.5%, there are two things one can do to mitigate this issue; (1) run the engine wide open occasionally and at the end of a cruise and (2) change oil at the recommended 100 hour oil change interval for our Hondas.

For high rates of observed or tested fuel dilution, say above 5% or "making oil" look for a failed thermostat, a leaking fuel pump, bad valve timing, or a bad injector (in that order).

As for kinematic viscosity, the lab uses 1 centistroke (cTs) lowering of average kinematic velocity as an indicator of <1% thinning. For 30wt oil, the average is 10.9 cTs. For future reference, 40wt is 16.3 to 12.5 cTs, 30wt is 12.5 to 9.3 cTs, and 20wt is 9.3 to 5.6 cTs. Aparently, thinning to the next lower oil grade maximum viscosity range is considered "moderate" thinning.

The marine grade (FC-W) spec imposes a higher minimum viscosity level, which means that FC-W oil will not thin out as much as automotive oil of the same viscosity under the same heat and rpm conditions.

So, I will use Honda or equivalent FC-W 10w-30 wt oil and change oil every 100 hours in order to stay under 3.5% fuel dilution and above 9.3 cTs. I also will obtain an oil analysis report at each oil change in order to stay ahead of any problems. I used Oil Analyzers, Inc.(http://oaitesting.com/) for this analysis and will for future analyses.

[DavidM]

Your description of the various parameters of an oil analysis and their causes makes sense to me as a retired chemical engineer. Thanks for posting.

My own experience is from a diesel engine perspective where fuel dilution is much lower, probably due to diesel's higher viscosity than gasoline.

David

[thataway]

Good information. I suspect that very few do regular oil analysis on their outboards. I would have absolutely zero concern about these two issues.

I change my oil once a year--There are some years we put less than 100 hours on the motors. However, in this case, it is typical for displacement speeds when doing the "Loop" or any other cruise which requires no wake or 5 mph speeds, to double the interval between oil changes.

There is also the school of thought that the number of gallons of fuel, rather than hours should dictate fuel change intervals.

I doubt that you did any harm by running at lower RPM. There are many of the very high hour outboards which spend much of their lives at low speeds. Generally the more you run the engine, the better it is for it--as long as the engine gets up to operating temperature.

[starcrafttom]

You really need a hobby.. I have 1200 hours on my honda 225 and just change the oil every 200 hours or every year. When I sold my 90 hp honda on the 22 it had a 1000 yours or so. That was in 5 years. next owner but 200 hours on it in 4 years then sold it. do not know where it is today but I beat its still running. Modern out boards just need to be flushed and oil changes on time. Also plugs every other year.

[JdaleH]

Thanks for the comments. I think the bottom line is to check oil levels periodically for "making oil" because that indicates a more serious problem. Otherwise, using the recommended oil at the recommended oil change interval will likely make fuel dilution a non-issue. I plan to do the oil analysis at each oil change for a while to see what the norm is for my Honda 135 on See-Ya, mainly because I have a scientific curiosity.