oil change - draining oil "cold"

skinny_monkey · 5 Nov 2019

C4Silver said:
Dunno, seems again like a logical suggestion but in my head I'm thinking about the hot engine cooling from hot to ambient temps with no oil in

When you turn the engine off, the oil will start cooling and dropping back to the sump. Your engine doesn't know or care if the sump plug is fitted or not.

MisterCorn · 6 Nov 2019

I'm with Infrasilver. If the car has been sat for some time, all that is going to get back to the sump will have drained there, you are then just draining the sump.
If the engine is warm/hot or has run recently, then you are also waiting for all of the oil which will drain back from the rest of the engine to get back to the sump, so it will take longer.

I usually drain mine cold and leave it until it is dripping slowly. No point waiting all night for the last 10ml when there is still 1.5l sat in the engine.

If the oil is dropped first, by the time the rest of the parts required for a service have been done it is time to put the plug back in.

MC

C4Silver · 6 Nov 2019

skinny_monkey said:
C4Silver said:

Dunno, seems again like a logical suggestion but in my head I'm thinking about the hot engine cooling from hot to ambient temps with no oil in

Click to expand...

When you turn the engine off, the oil will start cooling and dropping back to the sump. Your engine doesn't know or care if the sump plug is fitted or not.

I get that the engine doesn't understand that there is no Oil in there, I'm guessing you can see from my posts that I don't actually get the science behind the Oil expansion etc, my thinking was that from 90 degrees operating temps and cooling with no Oil in might be detrimental to the engines internals as the working parts contract to cold with 1.5 litres of oil in there as opposed to 9 ?

And I totally get the None overnight drain, why wait all night for a few drops when there's still over a litre in there, the reasoning behind that is perfectly logical.

skinny_monkey · 6 Nov 2019

C4Silver said:
skinny_monkey said:

C4Silver said:

Dunno, seems again like a logical suggestion but in my head I'm thinking about the hot engine cooling from hot to ambient temps with no oil in

Click to expand...

When you turn the engine off, the oil will start cooling and dropping back to the sump. Your engine doesn't know or care if the sump plug is fitted or not.

Click to expand...

I get that the engine doesn't understand that there is no Oil in there, I'm guessing you can see from my posts that I don't actually get the science behind the Oil expansion etc, my thinking was that from 90 degrees operating temps and cooling with no Oil in might be detrimental to the engines internals as the working parts contract to cold with 1.5 litres of oil in there as opposed to 9 ?

The working parts cooling won't be affected by anything, oil will start to drain down, leaving approx 1.5l around the engine. The remaining oil will either sit in the sump or drain out - either way, not doing anything with the engine. As soon as the engine stops turning, there's no oil pressure and so the oil is doing nothing with the working parts. The oil drains down and then engine cools in the same way except obviously, if you don't drain from hot, the engine takes longer to cool down as you have additional thermal mass in there.
Oil expansion, the volume occupied by a given mass of oil increases slightly with temperature (density decreases). So if you had 8l of cold oil in the sump, it might be 8.5l when it's hot.

oil change - draining oil "cold"

skinny_monkey

Montreal

MisterCorn

Fuji

C4Silver

Sao Paulo

skinny_monkey

Montreal

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