Must oil really be warm before draining?
Discussion
I have always made sure to drain oil warm but am now questioning whether that is really necessary, especially if left to drain overnight.
Seems to me that for both the engine and gearbox that when it is turned off a certain fixed amount of oil will drain down to the sump. When the sump plugs are removed sure warm oil will drain out quicker but if the sumplugs are left out overnight then surely the same total amount of oil will drain out regardless of whether it was done warm or cold.
Seems to me that for both the engine and gearbox that when it is turned off a certain fixed amount of oil will drain down to the sump. When the sump plugs are removed sure warm oil will drain out quicker but if the sumplugs are left out overnight then surely the same total amount of oil will drain out regardless of whether it was done warm or cold.
finlo said:
I've always been in two minds about this, draining warm is quicker but doing it cold has at least had a chance to drain back into the sump.
Seems to me the amount that clings to the inside of the upper parts of the engine is going to be the same whether it is drained warm or cold. Also if done cold any solids in suspension will have had a chance to drain back into the sump before draining starts and therefore more likely to get dragged out with the old oil.Not sure about a gearbox though, if done cold might that leave more oil inbetween the lower half of the gears, the bits that are under the oil level, as opposed to warm when maybe that would come out.
Ive drained cold when its sat overnight but i cant see a benefit in it really, some filter housings etc hold quite a lot of old oil and unless you make the effort to suck it out some will always remain.
Im of the opinion to change it regularly which for me on a daily driver is around 9 months or 5000 miles, for the sake of £30 i think its worth it.
Im of the opinion to change it regularly which for me on a daily driver is around 9 months or 5000 miles, for the sake of £30 i think its worth it.
Always when hot, 1/2 an hour on my petrol engines*, but i leave it several hours or overnight on my Diesel to inspect the pick up strainer (directly above drain plug on mine) for signs of carbon residue...early warning of failing injector seal.
People with the weird (just why? even Honda joined in with this bad joke) cambelt running in oil design on some petrol engines might consider doing this, an endoscope poked up the drain hole should do the trick in most sumps.
Good regular draining ensures even on my 18 years old Diesel the oil stays clean for almost 1000 miles after changing.
People with the weird (just why? even Honda joined in with this bad joke) cambelt running in oil design on some petrol engines might consider doing this, an endoscope poked up the drain hole should do the trick in most sumps.
Good regular draining ensures even on my 18 years old Diesel the oil stays clean for almost 1000 miles after changing.
- i have a Fumoto quick drain valve on our Forester (have used them before on other cars), the standard sump plug is a surprisingly large bore and the oil comes out like billio you can't help getting splashed, the Fumoto valve has made draining much nicer, the narrow bore of the valve makes hot draining preferable.
NickCLotus said:
I have always made sure to drain oil warm but am now questioning whether that is really necessary, especially if left to drain overnight.
Seems to me that for both the engine and gearbox that when it is turned off a certain fixed amount of oil will drain down to the sump. When the sump plugs are removed sure warm oil will drain out quicker but if the sumplugs are left out overnight then surely the same total amount of oil will drain out regardless of whether it was done warm or cold.
With enough time, yes it will eventually all move to the lowest point it can.Seems to me that for both the engine and gearbox that when it is turned off a certain fixed amount of oil will drain down to the sump. When the sump plugs are removed sure warm oil will drain out quicker but if the sumplugs are left out overnight then surely the same total amount of oil will drain out regardless of whether it was done warm or cold.
Whether that's minutes, hours, days, hardly worth worrying about.
With modern synthetics of generally "thinner" specification than mineral 20-50 from Jurassic Park it doesn't make much difference what the temperature is when you change oil. It's not as if new oil is a sluggish pour from the can in winter.
And whether you change 97% of the oil or 99% of the oil isn't going to make the blindest bit of difference.
On the other hand when changing fluid in an auto transmission the temperature can be absolutely critical when refilling and checking level.
And whether you change 97% of the oil or 99% of the oil isn't going to make the blindest bit of difference.
On the other hand when changing fluid in an auto transmission the temperature can be absolutely critical when refilling and checking level.
Smint said:
- i have a Fumoto quick drain valve on our Forester (have used them before on other cars), the standard sump plug is a surprisingly large bore and the oil comes out like billio you can't help getting splashed, the Fumoto valve has made draining much nicer, the narrow bore of the valve makes hot draining preferable.
Has it been reliable (no leaks etc)? I might fit one to my race car (sump plug is awkward to undo)
Smint said:
Just make sure before you leave it for hours that it isn't one of these ludicrous gems of anti-engineering where the oil pump can't prime itself and the oil needs to be back in the sump within 15 minutes or so.
Ford 3.2 as found in the Ranger, if I remember right. I’m sure there are others…LennyM1984 said:
Never heard of these. What a brilliant idea!
Has it been reliable (no leaks etc)? I might fit one to my race car (sump plug is awkward to undo)
No leaks, a well made item, had one on a previous Hilux and Merc.Has it been reliable (no leaks etc)? I might fit one to my race car (sump plug is awkward to undo)
Theoretically possible in rough terrain for string or debris to foul the catch, in reality it would be almost impossible to happen but i'm a belt and braces chap so a spring/jubilee clip or even a cable tie placed in the obvious position ensures that can never happen, i think on QuickDrainValve's site they show the a spring clip in the appropriate place.
I've thought about fitting drain valves but given the messier and slightly more embuggerant job is (usually) changing the filter, I can't help but wonder if the benefits offered work out less than they initially seem. The only two situations where they seem to make sense to me are:
1) you want to change your oil every few months but the filter annually. Then it really does seem a no-brainer.
2) you have a top mounted oil filter a la Mercedes, but don't trust Pela pumps.
YMMV of course.
1) you want to change your oil every few months but the filter annually. Then it really does seem a no-brainer.
2) you have a top mounted oil filter a la Mercedes, but don't trust Pela pumps.
YMMV of course.
TallPaul said:
Smint said:
Just make sure before you leave it for hours that it isn't one of these ludicrous gems of anti-engineering where the oil pump can't prime itself and the oil needs to be back in the sump within 15 minutes or so.
Ford 3.2 as found in the Ranger, if I remember right. I’m sure there are others…donkmeister said:
I've thought about fitting drain valves but given the messier and slightly more embuggerant job is (usually) changing the filter, I can't help but wonder if the benefits offered work out less than they initially seem. The only two situations where they seem to make sense to me are:
1) you want to change your oil every few months but the filter annually. Then it really does seem a no-brainer.
2) you have a top mounted oil filter a la Mercedes, but don't trust Pela pumps.
YMMV of course.
It was a no brainer on my Forester, the drain plug of which is larger bore than most car plugs i've ever come across, meaning that hot oil would come gushing out at a rate of knots and even with being prepared for it the damned stuff would splash everywhere unless you had a professional sieved drain bucket and the car up on a lift, draining with the Fumoto in place is a much more civilised affair for those of us lying on our backs.1) you want to change your oil every few months but the filter annually. Then it really does seem a no-brainer.
2) you have a top mounted oil filter a la Mercedes, but don't trust Pela pumps.
YMMV of course.
Even better with Diesel engines given how filthy the old oil usually is, not recommended for my Prado but because the oil strainer is situated directly over the sump plug i let it drain for a long time and then inspect the pick up and the Fumoto would make that impossible...injector seal blow by is one of the rare issues that trouble the 3 litre D4D engines, most owners who DIY service and who are aware do this.
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