Oil changes

[drynoc]

I've read about the necessity of the frequent oil changes in my boat ( new Yanmar 2GM20F, about 50 hours) but I use the engine so little that it doesn't seem sensible to do it that often. I go out on average three times a month, but engine usage only comes to about 15 minutes. That's 45 minutes a month, or maybe 9 hours a year. I know the oils can handle that - they last a lot longer in cars. How often are changes necessary at this usage?

[Siamese]

Stand by for a lot of opinions on this, and certainly you're going to hear that engine hours are only part of the story. How long the oil is in your engine is another big factor (regardless of how much it runs). As soon as you run your engine you introduce oxidants to your oil and it will be corrosive to your engine over time. Using the same oil for multiple seasons, even though you have low hours, would be harmful.

Opinions are going to vary a lot on how many months is practical, but personally, I wouldn't want to go over six without an oil change.

[DrB]

You really should run your engine hard and for 1/2 to 1 h every month or so to keep the diesel happy. You need to do that burn off any carbon build-up in the motor. The problem with running it only 15 minutes every time you go out is that the motor really never gets warmed up to burn off residual partially burned fueled and the carbon crud can build up.

So my recommendation is to do a couple of circles before you come in once every month for about 30 minutes with the engine close to wide open and at the end of the season change your oil/filter before you put her away for the winter. Oil and a filter are cheap compared to $5000 motor. Why risk it?

DrB

[CalebD]

One oil change per season is only the minimum number in my mind even if you only put minimal engine hours on per season. As others have already pointed out the oil inside your engine will pick up contaminants and in a diesel there is the possibility of sulphur mixing in and forming sulfuric acid (Caulder) which is very bad for metals. Also consider that when you do change your oil you do not necessarily get all the old oil out (depending on the pitch of your engine somewhat) so multiple oil changes make for overall cleaner engine oil. Changing the oil is like cheap insurance as is replacing your zinc.
One more thing: all oils are not created equal. Diesel engines use compression for ignition whereas gasoline engines use a spark and if you look at the fine print on the oil container you will see either an 'S' or 'C' rating (or both in the case of Rotella T). Oils with only an 'S' rating are not made for use in a diesel engine. This is also covered in Caulder's 'Boatowners Mechanical & Electrical Manual".

[petegingras]

Okay here goes, consider that with a new engine it’s going to have burs, little fragments of metal that are not totally removed during the manufacturing process. The engine is multiple stamped, aluminum and steel, components that come together to form the one unit. Those components either lie on one another to form a housing, like the cylinder bore or do their thing against other components, like the piston. Naturally that friction will cause those burs to frag into the lubrication oil. So I think yes the 50 hour is reasonable. Also a mechanic is going to, or you should desire, check the compression alignment of the piston. This is important if new, Yanmar warranties any irregularity.

You really should run your engine hard and for 1/2 to 1 h every month or so to keep the diesel happy. You need to do that burn off any carbon build-up in the motor.

And anther part of keeping that engine happy is keeping those gaskets lubricated with the oil, remember those gaskets are between all those components. Otherwise they’ll dry out without the oil and you’ll have oil leaks, and then an oily bilge. And the way the EPA is going oily bilges may be punishable by death sometime this century.

[hellosailor]

drynoc-
Oil changes in a boat are based on different factors from usage in a car. In a car, typically the oil gets broken down from heat, friction, etc. from the use of the engine. It also is contaminated by silicon grit (dust getting past the air filter) and combustion byproducts, and some fuel that gets past the rings, and sometimes coolant, and diluted by condensation--but not much of the last.
On the other hand, in a boat there is massive contamination from condensation every night inside the engine and oil pan. In a car that water literally "cooks off" after driving for 15-30 minutes. In a boat, with just short engine runs, it may not cook off at all, so the oil is degraded. Also, the air filter (if there is one) isn't great, so salt and silicon get into the oil at higher rates.
So in a boat, you are mainly changing the oil in order to dump the impurities that collect and form in it--much faster than they do in a car. And condensation forms, every night, regardless of whether you use the engine.

If you really want to put some science on it, for about $22 you can buy an oil test kit at an auto/engine shop or on the internet. You send off about three ounces of used oil, they'll send back an analysis of exactly what is in it and whether it needs to be changed. Great if you need 10+ gallons at a time...but cheaper for most of us to just change the oil, proactively.[g]

[BarryL]

Hello,

According to the service manual for my Universal M25, the oil and filter should be changed 75 hours, or once a season, which ever comes first.

Changing the oil once a year, right before winter layup, doesn't seem like that much work.

Barry

[hellosailor]

I've never quite appreciated the idea of changing the oil BEFORE layup. OK, the old oil is coming out, but that's mainly going to drain into the pan.

And the new oil? Will be full of condensation and useless before the new season starts, a complete waste.

No?

[erps]

I've never quite appreciated the idea of changing the oil BEFORE layup. OK, the old oil is coming out, but that's mainly going to drain into the pan.

And the new oil? Will be full of condensation and useless before the new season starts, a complete waste.

No?

I hadn't thought about that. Maybe draining the oil and then leaving it empty with oil filler cap and drain plug open is the way to go for lay-ups? Dirtly oil out and minimum condensation build up.

[sailingdog]

Not really, since condensation requires fairly large variations in temperature generally and higher levels of humidity--which you're generally not going to find in many areas in winter-time. Having clean motor oil in the engine over the long layover period makes a lot more sense than having the nasty complex of acids and such that are found in used motor oil for the same period of time.

Originally Posted by hellosailor

I've never quite appreciated the idea of changing the oil BEFORE layup. OK, the old oil is coming out, but that's mainly going to drain into the pan.

And the new oil? Will be full of condensation and useless before the new season starts, a complete waste.

No?