Engine Oil Change

[Ian_Rob]

I am running out of time to change my oil before my boat has to come out of the water in 14 days time. It is always said that you should drain when the engine is warm. How important is this? I would like to leave it until she is out and drain from the bottom [if I can get the drain screw undone) rather than using an oil extractor as previously but the oil will be cold.

 

[bert49uk]

Reason for changing oil when warm is it 'flows' better, if you are draining from bottom not a problem,

 

[chuzzlewit]

Hot oil is noticeably less viscous. But doesn't multigrade oil thicken when hot?

 

[prv]

I'd say it's definitely worth getting the oil warm if you'll be using a pela-sucker - I've done it without and it took ages, plus it didn't feel like it was getting it all out. But with a sump plug (you have checked the engine has one, I take it? Not all do...) it's probably less of a problem.

Pete

 

[Otter]

Last winter I ran the engine for ten minutes but the oil was only tepid when it came out and it was unbelievably difficult to extract it with a pella type.

 

[lw395]

Not a problem to drain the oil cold.
Just leave it draining for a few hours if you really want as much out of it as possible.
I would be more concerned with getting the new oil around the engine.
If it has a decompressor, I'd crank it over decompressed to make sure the oil filled the filter and got all around the motor.

 

[Spirit of Glenans]

Not a problem to drain the oil cold.
Just leave it draining for a few hours if you really want as much out of it as possible.
I would be more concerned with getting the new oil around the engine.
If it has a decompressor, I'd crank it over decompressed to make sure the oil filled the filter and got all around the motor.

If no decompressor, you could put it in gear and turn it over with the prop - make sure the ignition is off!

 

[Poignard]

If you have electrical power available when you lay up you could warm the engine up using a fan heater. (Perhaps not, if it's a petrol engine )

 

[Skylark]

I am running out of time to change my oil before my boat has to come out of the water in 14 days time. It is always said that you should drain when the engine is warm. How important is this? I would like to leave it until she is out and drain from the bottom [if I can get the drain screw undone) rather than using an oil extractor as previously but the oil will be cold.

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.

 

[JumbleDuck]

If no decompressor, you could put it in gear and turn it over with the prop - make sure the ignition is off!

What is this "ignition" of which you speak, and why would it need to be off?

 

[James_Calvert]

As others have said, much easier to extract the oil when hot, particularly if you have to pump it out through a small diameter tube stuffed down the dipstick hole. But as the aim of doing the oil change at the end of the season is presumably to provide a bit of extra protection from the fresher oil, there's not much point in doing it unless you run the engine afterwards, is there? So if you can't, for some reason, organise running the engine whilst the boat is ashore, and you lift the boat out before the oil change, I guess you won't do much harm by just leaving it with the old oil in, will you? Unless of course you know it's seriously contaminated eg with seawater or something. But be sure to change the oil before you run the engine again anyway! What does your engine manual recommend - change oil before or after winter lay-up?

 

[30boat]

If no decompressor, you could put it in gear and turn it over with the prop - make sure the ignition is off!

Traditional diesels will start with the ignition key in the of position unless the fuel cut out is cable operated and is left in the pulling position.Anyway it's impossible to start a diesel by hand turning the prop.

 

[lw395]

... I guess you won't do much harm by just leaving it with the old oil in, will you? Unless of course you know it's seriously contaminated eg with seawater or something. .....?

I think you guess wrong.
Old oil has acid byproducts in it.
Much better to leave a motor standing with new clean oil in it.

 

[MM5AHO]

What is this "ignition" of which you speak, and why would it need to be off?

or even remove the spark plugs from that diesel engine?

 

[James_Calvert]

I think you guess wrong.
Old oil has acid byproducts in it.
Much better to leave a motor standing with new clean oil in it.

I won't argue with that. But if you just change the oil in the sump without running the engine, surely you might as well not have bothered?

 

[lw395]

I won't argue with that. But if you just change the oil in the sump without running the engine, surely you might as well not have bothered?

Hence I suggested cranking the motor to get oil around the engine.
It doesn't need to actually run.

Personally I like to crank the motor every month or so to keep a trace of oil on everything, hopefully.

 

[prv]

If no decompressor, you could put it in gear and turn it over with the prop

If you can turn the engine over by hand without a decompressor, surely there's something badly wrong with it?

Pete

 

[30boat]

Hence I suggested cranking the motor to get oil around the engine.
It doesn't need to actually run.

Personally I like to crank the motor every month or so to keep a trace of oil on everything, hopefully.

That's a terrible idea.You'll wear out the engine by doing that.

 

[James_Calvert]

Hence I suggested cranking the motor to get oil around the engine.
It doesn't need to actually run.

Personally I like to crank the motor every month or so to keep a trace of oil on everything, hopefully.

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.

 

[VicS]

Hot oil is noticeably less viscous. But doesn't multigrade oil thicken when hot?

No but it does not thin quite as much as a monograde oil

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. Stll thiinner than when it was cold but not as thin as a hot 20 grade.