Why change oil twice?

[Biobob Catalina 27]

Hi All, Kinda new both to sailing and deisel engines, I have seen recomendations to change the oil when it comes out of the water in the fall, and again before it goes back in the spring. Can someone explain the reasoning for re-changing in spring when it hasn't been used except to fire it up to make sure the new impeller is in correctly, does the oil go "bad" over the winter? I have a universal 18 in mine, and want to do all maintanence correctly, but not sure why this is recomended.

 

[Don Crowther]

Nope can't help you. I change mine in the fall and that's it.

 

[Doug4bass]

Fall and spring for me. Always have.

 

[Don Crowther]

What would happen if you just dumped it the fall and left it empty until spring. The oil only sits in the pan and pump screen over the winter.

 

[justsomeguy]

I think atmospheric moisture that could condense inside the crankcase is the main concern regarding this practice.

 

[quadrille38]

Not sure but I think some folks subscribe to the theory that when you change in the fall it has all winter to drain down leaving the engine less lubricated when spring comes. And that changing it in the spring allows for pouring oil over the parts to relubricate.


Problem with this theory is that you really have to run the engine to get it hot enough for the oil to flow out so you've started it anyway.
If that is the reason there is an easier way. When changing the oil in the fall refill with 90% of the oil required and reserve the remaining 10% to put in before starting the engine in the spring. That way it flows down over the parts.


Mechanic I talked to said this is unnecessary as the oil coats the parts and as soon as the engine turns the oil pump starts its work so there is plenty of lubrication.

If its potential condensation question what I've been told is that running the engine in the spring until it's good and hot will take care of any moisture that might be in the oil.

 

[Stu Jackson]

Problem with this theory is that you really have to run the engine to get it hot enough for the oil to flow out so you've started it anyway.
If that is the reason there is an easier way. When changing the oil in the fall refill with 90% of the oil required and reserve the remaining 10% to put in before starting the engine in the spring. That way it flows down over the parts.

Nope, an easier way is to hold the kill switch/cable and turn the engine over a few times before you start. This will move the oil around.

While we keep our boat in the water and use her year round, a double oil change is an urban myth to me.

Everything above the oil level at rest is subject to whatever happens inside anyway, so full or empty of oil is rather meaningless.

 

[Ralph Johnstone]

Can someone explain the reasoning for re-changing in spring when it hasn't been used except to fire it up to make sure the new impeller is in correctly, does the oil go "bad" over the winter?

I don't think the oil goes bad over the winter (about five months) with time as there's no carbon, sulphur, water, or other etceteras in there to degrade the oil.

However, as I know I'll put about 100 hours on the engine for the summer (you can see we don't get much wind here) I like to get about 20-30 hours out of the previous fall's oil change before installing new oil for another 60-70 hours in the summer.

 

[thinwater]

Nope, an easier way is to hold the kill switch/cable and turn the engine over a few times before you start. This will move the oil around.

While we keep our boat in the water and use her year round, a double oil change is an urban myth to me.

Everything above the oil level at rest is subject to whatever happens inside anyway, so full or empty of oil is rather meaningless.

^^ The correct answer.

While the oil certainly collects a miniscule amount of moisture, this will reach equilibrium levels soon after the engine warms up, the excess leaving through the breather. Far worse is the sailor that only runs the engine to the end of the jetty, never running it hard and taking all season to go though a tank of fuel. Use the engine.

 

[centerline]

Hi All, Kinda new both to sailing and deisel engines, I have seen recomendations to change the oil when it comes out of the water in the fall, and again before it goes back in the spring. Can someone explain the reasoning for re-changing in spring when it hasn't been used except to fire it up to make sure the new impeller is in correctly, does the oil go "bad" over the winter? I have a universal 18 in mine, and want to do all maintanence correctly, but not sure why this is recomended.

It is a practice that is recommended by the same folks that recomend that you keep your fuel tanks full to prevent condensate from collecting in it... its an old practice that has been printed and reprinted over the years, but modern oils are much better protected from enviromental degradation that they once were.

And as has already been said, the small amount of moisture that may potentially collect in the crankcase due to any condensate, will boil off in about 10 minutes after it comes up to operating temperature...

I believe in keeping my fuel tanks reasonably full, but I would never follow the practice of discarding perfectly good oil.

 

[Doug4bass]

I would. I put approximately 100hrs on my engine a year. Oil is cheap, engines are not.

 

[Kings Gambit]

The practice might be a "hand-me-down" or "tribal-legacy" one from the autoworld, where mininally once-annual oil changes are recommended by many automanufacturers irrespective of mileage. I'm pretty sure some marine diesels are recommended to be on that schedule as well. Annual could easily mutate to semi-annual in the case where oil has been sitting repeatedly below the freezing point of water for several days to weeks at a time. I'd probably do mine if the boat were coming off the hard in New England after a long winter; get it over with early and go sailing. When putting the boat up it makes sense to reset everything for the next use even if in the end you go a step further in engine maintainence.

 

[Ron20324]

... there's no carbon, sulphur, water, or other etceteras in there to degrade the oil....

+1 to what Ralph said. The idea of taking the oil out in the fall in the first place is to remove all the engine-eating chemicals.

I recall (but never used) for car engines a "flush" oil. You'd drain the old oil, add the flush oil, run the engine for some period of time to get the remains of the old oil into suspension, then drain and add "good" new oil. I don't recall if the "flush" oil could be left in the engine over the winter?

 

[Ralph Johnstone]

I recall (but never used) for car engines a "flush" oil. You'd drain the old oil, add the flush oil, run the engine for some period of time to get the remains of the old oil into suspension, then drain and add "good" new oil.

Oh crap ................... now you're reeeeeeeaaaaaaalllly going back in time .

Yes I remember flush oils. The adverts ran "you better use our brand of flushing oil or your engine will fall apart". I have to wonder if that stuff was the forerunner of the detergents found in modern engine oils.

 

[centerline]

I would. I put approximately 100hrs on my engine a year. Oil is cheap, engines are not.

Yep, its better to be safe than sorry...

100 hours is a lot of hours on the oil if the boat is being moved from its slip out to the sailing area with the engine barely coming up to operating temps, and then back in the same way.
but a diesel engine in decent running condition that gets run for hours at a time at a higher rpm, such as when motoring, will be able to go longer between oil changes, due to the oil staying clean longer...

A cold engine running at a low rpm has a lot more deposits dumped into the oil and out the exhaust... running it for a good amout at a higher temp will allow some of the harmful moisture and acids to be cooked off...

 

[thinwater]

Yep, its better to be safe than sorry...

100 hours is a lot of hours on the oil if the boat is being moved from its slip out to the sailing area with the engine barely coming up to operating temps, and then back in the same way.
but a diesel engine in decent running condition that gets run for hours at a time at a higher rpm, such as when motoring, will be able to go longer between oil changes, due to the oil staying clean longer...

A cold engine running at a low rpm has a lot more deposits dumped into the oil and out the exhaust... running it for a good amout at a higher temp will allow some of the harmful moisture and acids to be cooked off...

All of which has nothing to do with changing it again in the spring. No one has presented an actual reason. You would do far more good changing it mid-season.

 

[Sprega]

A couple of thoughts. If my motor has been unused for quite a while,I pull the compression release and crank the motor with out starting it until I see the oil pressure gauge rise. This way I know that the bearing surfaces have oil to them before firing the motor. I always do this in the spring before I change the oil. This way I can warm the oil to operating temp before draining it. It drains much better warm.

 

[centerline]

All of which has nothing to do with changing it again in the spring. No one has presented an actual reason. You would do far more good changing it mid-season.

I agree.

 

[centerline]

If my motor has been unused for quite a while,I pull the compression release and crank the motor with out starting it until I see the oil pressure gauge rise. This way I know that the bearing surfaces have oil to them.

This is a good practice if the motor is GOING TO BE setting for quite awhile...
When you shut down a hot engine and walk away from it, the hot oil drains away from all the bearing journals... so if you were to wait til the engine and oil was cold, then crank it over so the oil pressure comes up, and then let it set that way, the cold oil wont drain away as readily as the hot oil did.. and you will be protected a bit better.

There are oil additives that can offer even better oil adhesion if one is worried about it for long term storage

 

[Doug4bass]

Oil is cheap.....so is my labor. And... with my boat being on the hard for 7 months in da great white north...well then it gives me the warm fuzzies to change the oil in the spring.