Is it possible for some old oil to always stay in the pan? 

"SantaRita" (SantaRita) 08/06/2017 at 09:31 • Filed to: None

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I think it’s possible that I never dump out old oil completely. The pan drain being 1/4" above the bottom of the pan on my car, I’d have to be in a steep incline.

I know from doing trans flush that the sediment and thicker stuff will aggregate in the bottom, sort of making a film.

Is engine oil the same way? Is Oil draining back down slow enough to layer like a fancy cocktail? Will the pan accumulate some thicker slurry of oldest oils in the bottom over time?

Or is all new and old oil somehow agitated and mixed in the very bottom there?

e36Jeff now drives a ZHP > SantaRita 08/06/2017 at 09:38

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That’s pretty much the reason why you are supposed to change the oil on the engine while it’s hot. Any contaminants that would otherwise settle to the bottom of the pan and not come out with an oil change should still be mixed in with the oil and anything left over will be fairly devoid of contaminate.

SantaRita > e36Jeff now drives a ZHP 08/06/2017 at 09:45

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True, it’s also why some plugs are magnetic, to get more of it out, but I think in this pan, you’d still leave 1/2 cup of older oil in it hot or not, which isn’t a lot.

I was looking at my top end, an above the cams are a few pools of obviously very dark oil, under the cams, the fresh oil is in golden pools. Got me wondering if my pan has a Layer under the height of the pickup tube/drain that could be less circulated.

e36Jeff now drives a ZHP > SantaRita 08/06/2017 at 09:50

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Well, sure. Short of tearing down the engine and hot dipping the whole thing you’ll always have leftover oil. I’d wager you always have at least 1/2 cup in various places that physically can’t drain back to the pan under gravity power, plus the oil coating the various intervals. But your oil change interval should never be so long as to allow your pan to build up a layer of gunk like a transmissions pan can, and as long as you change it hot that 1/2 cup is going to contain minimal contaminates and will soon be diluted into your fresh oil and become meaningless.

Flavien Vidal > SantaRita 08/06/2017 at 09:58

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Hum... not sure... God way to do it, empty your oil, start your car, make it go forward, backward, shake it a little, while keeping some sort of receptacle taped under it... That should remove all the oil :)

DipodomysDeserti > SantaRita 08/06/2017 at 10:12

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There will always be a bit of oil left, but as long as you’re changing it while the oil is hot it won’t be the same bit of oil over and over again.

MM54 > SantaRita 08/06/2017 at 10:43

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If you always change it cold, yes. If you change it hot (like you should) it’s negligible.

gogmorgo - rowing gears in a Grand Cherokee > SantaRita 08/06/2017 at 11:27

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I usually drop in about a cup of fresh oil and let that drain out before putting the plug back in. Whether it does anything other than flow right out the bottom I couldn’t really say, but it does make me feel a little better about what’s left in the bottom of the pan.

But in reality, if there’s stuff accumulating there at all, it’s probably not likely it’s getting picked up by the pump, and any deteriorated oil will be pretty diluted with fresh oil, and the filter will catch most debris, so long as you change it.

AMGtech - now with more recalls! > e36Jeff now drives a ZHP 08/06/2017 at 11:48

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In my experience buildings engines, a completely dry engine will usually take .5-1 quarts more than it would during an oil change, depending on the specific engine of course.

e36Jeff now drives a ZHP > AMGtech - now with more recalls! 08/06/2017 at 11:52

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I’m not at all shocked by that. I’d imagine the bigger the engine the more oil it can hold when “drained.”

AMGtech - now with more recalls! > e36Jeff now drives a ZHP 08/06/2017 at 12:02

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Exactly.

Cabrio'sNStrat's > SantaRita 08/06/2017 at 15:19

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I’ll pop in with my $.02. I have been in the chemical etching industry for a while and have to deal with cleaning spent chemical from machines. The thing we go for is what percentage of left spent acid will cause us issues? You’ll never get it all out so we design SOP to allow for it. When your dealing with micron tolerances it makes a big deal. It seems on cars the manufacturer would know what amount of old oil can stay and not cause and problems, and place the plug/design the oil pan for that.

SantaRita > Flavien Vidal 08/06/2017 at 16:00

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Terrible idea ha

SantaRita > SantaRita 09/19/2017 at 12:20

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for anyone who reads this, yes, of course, I needed a new engine.