How important is it to drain oil hot?

[M3 Mitch]

Everybody "knows" that draining your engine oil when hot is "better" (gets more crud out, drains faster), but reading a book on oils and filters I bought from Noria, they suggest that draining cold is just as good.

I'm wondering about say a motorcycle that you want to change the oil going into winter storage, and for whatever reason you don't get it done till the snow flies.

Seems to me that in this case the best thing would be to drain the old oil cold, then replace the oil, maybe take the spark plugs out, spin the motor good to distribute the new oil, and call it good.

Or would it be better to idle the motor till the oil is at least warm?

For purposes of discussion consider that actually driving the vehicle is not possible.

Anybody got any data? How would you tell the difference between a motor that had hot drains vs cold drains anyway? Seems to me if you don't leave the oil in for a rediculously long time it wouldn't much matter anyway.

TIA for any data, info, or even just opinions!

 

[Kestas]

I think draining it warm is not as important as getting all the old oil to blend in with the new oil before storage.

 

[JHZR2]

Is it THAT toug to change it before storage? Id probably prefer to change it a week or two beforehand, and then still use it... So long as it got to temp before being put away, I would think it not as big an issue.

I would at least start it to get everything churned up in the sump, if I couldnt get it full hot. A few seconds to a minute of idling is far better than idling it to temp - that will cause a lot more wear.

JMH

 

[Rick in PA]

Just an observation/opinion:

Years ago my brother and I rebuilt a motor. When we were done, we filled it with SAE30 and my brother told me to hold the RPM at 2000 for (I think) 15 minutes, then drop the oil. The oil was HOT and it just gushed out of the crankcase when I pulled the drain plug (remember it was SAE30).

Ever since that time, I've been a big proponent of draining motor oil HOT. I'll even fast idle a motor at 1500-2000 RPM for 5 minutes to make sure it's hot.

 

[obbop]

Pondering.......... visualizing the engine innards with oilinside.

Hmmmmm...... warm oil. Engine has been running. Oil distributed, clinging, slowly....slowly oozing down, obeying gravity's law.

Minute particles of metal and other crud within the oil, also flowing downwards.

Pondering further..... engine and oil cold. Perhaps many hours since ran. Except where barred by obstructions the oil has flowed downwards about as much as it is going to. Suspended crud within the oil except where friction or another factor has caused the particle to be left behind.

Pondering further..... seems to me it may be best to change the oil when it's cold, when the maximal amount has descended to the lowest point(s) of the engine. And, with the oil thicker, not thinned out by the heat, wouldn't the oil be likelier to drag along the unwanted particles with it?

I generally dump a new quart of oil into the engine while it is still in the draining mode to assist in removing suspended particles inside the oil pan. Figure it can't hurt.

No scientific data to support my pondering but it seems that cold drains MAY be the way to go.

 

[TallPaul]

obbop has a good point on the thicker oil dragging along more particles. I have drained cold and the main thing is that the last time it was shut down it was good and hot. You would not want (IMO) to run the car cold from the drive way to the garage and they later drain the cold oil. Another nice thing about a cold drain is the filter tends to drip a lot less if at all when you remove it.

 

[Vspec]

OOORRR, drain the oil at night after a long drive hot, and let it drain over night, then finsh the change the next day! Ho-ho, thats a good oil change. Dumping clean oil though a engine sounds like a sound idea, but what about this.

Me and my brother discussed using a high-out put air pump and making a fitting that would screw into the oil fill, with a fitting on the top side for the air-pump...say a tire pump, or something along those lines. You then turn it on with the drain plug out and use air to blow the inside of the motor clean of all sorts of shizzle. Thoughts?

 

[got boost?]

the most important thing is that when the oil is changed hot, there is still a layer of oil on the engine parts so the startup doesn't do as much damage. it is best to get the change and restart the engine in 1/2 hour or so.

 

[Drew99GT]

quote:

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Originally posted by got boost?:
the most important thing is that when the oil is changed hot, there is still a layer of oil on the engine parts so the startup doesn't do as much damage. it is best to get the change and restart the engine in 1/2 hour or so.

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Hmmmmmmm, wouldn't it be just the same as starting an engine stone cold the 1st time each day?

 

[Tosh]

I don't think pouring new oil in to help 'flush' out old oil would have the desired effect, as it just runs down one corner of the engine. But it would possibly help dilute the nastiest glob resting on the lip inside the drain plug.
Draining the oil hot ensures that the oil drains out in a reasonable amount of time. If it's cold, it will need to drain longer to drain the same amount of oil. Thick or thin, cold or hot, the oil already has the harmful things in it, and doesn't care about 'dragging' things around. All the 'dragging' happened immediately after shut down, thanks to gravity, presumably when hot.
Pumping or blowing it out with air? Well, it would help get things moving initially, but the air velocity you're imagining is mostly gone as the air moves around the passages and expands. The main airflow would take the path of least resistance, which probably would be down that same corner of the engine leading to the sump. It's not like blowing out a wet garden hose.
To specifically address putting away an engine for winter, I happened to be reading the owner's manual for a golf cart yesterday. It mentioned nothing about the oil (except to pour some heavy oil into the spark plug hole), but was obsessed with getting every drop of fuel out of the carb....

 

[1sttruck]

I drain the oil when warm; cold takes too long sometimes, hot oil burns, but warm oil is like warm porridge, just right. If you're worried about leaving dirty oil you need to refill with fresh oil, run it a bit and drain in order to flush. A local store had some 76 oil for about 75 cents a qt, so for less than $4 you can use 5 qts as a flush for peace of mind if needed.

 

[ryansride2017]

"the most important thing is that when the oil is changed hot, there is still a layer of oil on the engine parts so the startup doesn't do as much damage. it is best to get the change and restart the engine in 1/2 hour or so."

"Hmmmmmmm, wouldn't it be just the same as starting an engine stone cold the 1st time each day?"

Sometimes it's just great to sit back and read everyone's replies

 

[obbop]

Note to those doing the extended "drain thing."

Never happaned to me but there are reports of too-long drain periods affecting the oil pump deep inside the heart of yer' motorvator.

Read that a FEW folks have had to "prime the pump" in order to get the oil pump functioning properly again.

No first-hand experience and unsure if some engine-types are more prone to this oil-pump-losing-prime problem but it IS something to be aware of.

Perhaos someone who has experienced this problem could shout out and inform us of the factoids.

 

[road_rascal]

I really don't know if it makes a difference one way or another. I have the wonderful task of changing oil in all of the power equipment in my plant (John Deere tractor, Honda riding mowers, Toro riding mowers, snowblowers, etc) and I drain it out hot or cold. I always let it drain at least a good 1/2 hour and pre-fill the oil filter when applicable.

 

[Tosh]

Keep yer pondering and yer wives tales to yerself!

 

[mechtech]

Hot oil drains faster than cold oil.
Hot oil hurts more than cold oil.

 

[Shannow]

quote:

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Originally posted by mechtech:
Hot oil drains faster than cold oil.
Hot oil hurts more than cold oil.

---

Driving around the block into the back yard gives me warm oil, which both flows better, is nicer on the hands, doesn't overshoot that pan (horizontal drain plug), and hopefully has at least mixed any junk at the bottom of the pan back in a bit.

 

[blupupher]

Just curious, how much "junk" do you think is sitting at the bottom of a pan after sitting for several hours (or days even)? I have left oil that I drained in clear containers and not seen anything drop out of suspension. If I had "junk" in the bottom of my pan, I would have to wonder what was wrong with my filter or the engine itself.
And for the overnight drainers, really, how much more oil do you get out compared to a 5 minute drain?
Boost, nothing personal, but that is silly. For starters, you pour your oil into the engine, and while not getting everywhere, it does coat much of the engine. Plus a layer of oil will stay on the engine parts for a few days no matter what. As Drew said, same damage as starting the car for the first time of the day (which you would have to do to get the oil warm anyway.
I usually drain my oil when cold, mainly because I don't like burning myself. Since I have a Fumoto valve now, I may do warm or even hot drains, or may stay with cold ones, I just depends on how I feel at the time.

 

[Ray H]

Pondering ... oil is not a homogenous, single molecular weight brew, but rather a mixture of several base stocks and an additive package ... further pondering ... oil cold, heavier molecules no longer in random suspension, but now semi-congealed with wear particles and partially oxidized organic crud in bottom of sump ... further pondering ... drain plug removed, lighter molecules rush out leaving nasties glop behind ... further pondering - is this remaining concentrated witch's brew something any sane person would want mixed in with fresh, perhaps expensive, motor oil?

 

[1sttruck]

With a 6 qt sump that drains 5 qts you only have 83.3% fresh oil with an oil change. The 2nd oil change produces only 97.2% fresh oil, and the third still only produces 99.5% fresh oil. The fourth oil change produces a barely acceptable 99.92% fresh oil, and the fifth oil change finally gets one to 99.99% pure, fresh oil. Note that filters need to be changed too in order to get a 5 qt drain. If you only change the filter the first time and only get 4 qts out thereafter it takes eight oil changes to get 99.99% pure, fresh oil.

:^)