Engine Oil Change

[vyv_cox]

That would certainly help. But have you spotted, for example, what happens to the oil delivered into the rocker box when you are cranking the engine around by hand to adjust the tappets? It probably just splodges out in one place and runs straight back into the sump. Is it doing any better in lubricating the cylinder walls (for example)? I'd rather run it for a good while if I could.

Oil is delivered to the big end and main bearings directly by oil pressure, although plain bearings actually need very little pressure to develop their own hydrodynamic pressure. It is delivered to the cylinder walls in various ways, mostly by squirting from somewhere, maybe from the big end caps or from the gallery. In a partly worn engine it is debatable whether turning a cold engine over on the starter motor alone can develop sufficient pressure for squirting to be effective, due to increased clearances in the pump. I suggest that it might take quite an appreciable time, as a guess 30 seconds, for everything to be lubricated.

 

[nigelmercier]

Over simplified but a 20/50 multigrade oil has the viscosity of a 20 grade oil when cold but when hot has the viscosity of a 50 grade at that temperature...

With these three words, something that has often baffled me is made clear. Thank you Vic.

 

[lw395]

That would certainly help. But have you spotted, for example, what happens to the oil delivered into the rocker box when you are cranking the engine around by hand to adjust the tappets? It probably just splodges out in one place and runs straight back into the sump. Is it doing any better in lubricating the cylinder walls (for example)? I'd rather run it for a good while if I could.

If you are going to start it, then you should let it run long enough to get up to temperature, to remove the water create by combustion.
Cranking a diesel decompressed sprays the cylinder walls with diesel. You can do worse than that.
The crank does not have to throw much oil on the cylinder to lubricate it.

Whatever you do, the walls will mostly drain of oil between using the engine.
If the engine is hot, the oil will run off the cylinder walls more quickly.....
Some of us prefer semi-synthetic oil for its tendency to remain on cylinder walls etc better than 'liquidised dinosaur', but that's not a popular view on here

Personally, I see a lot of merit in leaving the boat afloat and using the engine regularly through the winter.

 

[rotrax]

No.

Put simply a 14/40 will be as viscous as a 10 weight monograde when cold, and as viscous as a 40 weight monograde when hot. A 40 weight monograde is like hot piss at operating tempreture-thinner than a 10 weight cold and much thinner than a 40 weight cold.

Multigrade oil does not thicken when hot, but retains its viscosity when hot due to the long chain molecules in the additives.

 

[VicS]

Multigrade oil does not thicken when hot, but retains its viscosity when hot due to the long chain molecules in the additives.

No it does not retain its viscosity but it thins less than a monograde oil. See my earlier post.

Illustrated here comparing a SAE 5W40 multigrade with straight SAE 5w and SAE 40 oils. Note the intersections at 0C and 100C

 

[30boat]

Good reading here
http://motorcycleinfo.calsci.com/Oils1.html

 

[SteveTibbetts]

Confused. I didn't get chance to do my planned oild and filter change before lift out and now have a boat ashore with oil and filter that are both 'cleanish'. They were both changed mid-season after a longtime trip under engine. Prior to the previous change before the trip the oil had sat for over 5 years I think


So.. Do I leave it till lift-in in April? Change cold it before the first frosts? Try and warm it with the impeller and thermostat out?

 

[prv]

Try and warm it with the impeller and thermostat out?

If you want to warm it by running the engine, don't try to do it without water or you'll just melt a hole in the exhaust.

Pete

 

[James_Calvert]

I'd leave it - especially as it's had a recent change.

It hasn't come up in this thread yet, but there's an argument for leaving the oil change until the spring anyway, as this is a better way of getting out any condensation that may have formed inside over the winter.

But I'm no expert and happy to be advised, by Vyv_Cox for example.

 

[vyv_cox]

Confused. I didn't get chance to do my planned oild and filter change before lift out and now have a boat ashore with oil and filter that are both 'cleanish'. They were both changed mid-season after a longtime trip under engine. Prior to the previous change before the trip the oil had sat for over 5 years I think


So.. Do I leave it till lift-in in April? Change cold it before the first frosts? Try and warm it with the impeller and thermostat out?

These days, with a nice safe marina berth in which to carry out all my pre-lift maintenance before the big day, I change my oil and filter on the water immediately beforehand. In the old days when the boat lived on an exposed mooring I always did it in the yard after haul out. Easily done, all you need is a water supply. Put a bucket in the cockpit filled with a hosepipe. Take a hose from it to the raw water pump and run the engine for ten minutes or more. Definitely do not remove thermostat and impeller. The oil will then be warm enough for a Pela, although it may still take some time to suck it all out, plus you have the bonus that the water side has been well flushed. Remove the impeller and drain the exhaust trap to overcome any possible feezing issues.

However, the sky is not going to fall in if you don't change oil until the Spring. Not ideal but not a disaster. The condensation issue is a non-starter, half an hour under engine will vent all water vapour through the breather. But recent research into diesel tanks has shown that the old story about tanks breathing in atmospheric moisture was started by an old wife - no truth to it whatsoever. I feel certain that the same applies to crankcases.

 

[lw395]

Confused. I didn't get chance to do my planned oild and filter change before lift out and now have a boat ashore with oil and filter that are both 'cleanish'. They were both changed mid-season after a longtime trip under engine. Prior to the previous change before the trip the oil had sat for over 5 years I think


So.. Do I leave it till lift-in in April? Change cold it before the first frosts? Try and warm it with the impeller and thermostat out?

Sounds like any corrosion that's likely to happen will have happened over the last 4 winters?
If the engine has not run many hours, and you used a fairly good oil, it will have the capacity to absorb the acid products.
It's oil that is pretty much ready to change that I'd make a real point of not leaving in over winter.
Or oil that has done a lot of short trips, never getting hot, collecting a lot of water.

Of course the more you change the oil the better, but pragmatically, we have to draw a line somewhere.

Take a look at what's on the dipstick.
Does it feel like oil?
Does it smell like clean oil or like a knackered ford transit?
Is black goo, or clear oil with a black tint?
Is the engine 'precious metal' or just something you need to keep in saleable condition for the next few years?

 

[charles_reed]

Don't know of any boats where there is sufficient room to get at a sump-bottom plug.
Usually I just leave the old oil in the engine, unless close to the 250/100 hr change intervals.
Water condensation in part-empty tanks, IMHO load of codswallop and in oil in sumps if changed a recommended intervals, shows no benefit with end-season changes.

 

[prv]

Don't know of any boats where there is sufficient room to get at a sump-bottom plug.

Our previous boat had plenty of room to get at the bottom of the sump - in effect the engine was suspended between the two sides of the hull with a deep bilge underneath. However, the 2GM20 does not have a plug! So I still had to use a Pela-sucker through the dipstick tube. We had the engine rebuilt by Marine Power, and I asked if they could perhaps fit a plug at the same time, since it would be so much easier. But they said the metal of the sump wasn't thick enough to tap a thread into.

On our current boat it would be fairly easy to remove a plug, though it would probably need a flexible tray (like one of those silicone baking tins) to get into position past the engine beds. Again, the engine doesn't have a plug, though this one does have a drain tube attached to the sump which you can put the sucker into instead of using the dipstick.

Pete

 

[rotrax]

No it does not retain its viscosity but it thins less than a monograde oil. See my earlier post.

Illustrated here comparing a SAE 5W40 multigrade with straight SAE 5w and SAE 40 oils. Note the intersections at 0C and 100C

If you read the first part it is obvious I am aware of that.

I will alter the bit you disagree with a tad to:-Multigrade oil does not thicken when hot but loses less vicosity than a mono grade due to the long chain molecules in the additives.

OK?

 

[Ian_Rob]

Why not simply get on with it in the next 14 days?

Once she's out of the water your options become less. If you can't get the drain scew undone for any reason, you'll be kicking yourself all winter.

It's an hours job to get the oil warm, vacuum it out, replace oil and fuel filters and refil with fresh. Job done. Relax.

Well, I will go ahead and do it before she is lifted it but I live 260+ miles from the boat and it would just have been easier this year because of work commitments, to have done it later.

Thanks for all the replies and the background info.

 

[Otter]

we've got a plug but no way would I use it. The engine is 1979 and runs sweetly but the thread on that plug - would I trust undoing it and up again? Crossed thread there and I'm in for a large bill. Pella is a pain but it works, next time I'm running for 15 minutes at least, I want hot oil.

 

[lw395]

Pela should work fine on cold oil, what's the rush?
Just pump it up and let it do its job.

Unless the tube is partly blocked, as happened to mine using it to clean crud out of diesel tanks.

 

[Daydream believer]

Water condensation in part-empty tanks, IMHO load of codswallop .

Codswallop or not the only year i did not fill my tank for winter I found i had diesel bug the following season

 

[30boat]

Betas are great for oil changing because they come with a pump connected to the sump.Makes changing oil an esay and clean job.

 

[Otter]

Betas are great for oil changing because they come with a pump connected to the sump.Makes changing oil an esay and clean job.

Got one of those on my 1970's Thornycroft - but the seals have gone. It also takes a huge amount of oil so a bit of a pain.