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Used Motor Oil Settles

A while back I finally dumped some changed out motor oil that had been sitting for about 9 months in a sealed plastic container. As I poured it into a recycling tank, I noticed it looked as clear as fresh oil from a factory container. Later I looked closely at the plastic tub it had been in, and there was a thin black film on the bottom.
I wonder if thoroughly settled oil might be nearly as good as new?

Tell me it wasn’t Pennz. I have no idea but I sure wouldn’t use it. At any rate I was told years ago that some oils suspend the garbage within the oil and other oils like Pennz, drop the garbage out so that it collects in the engine. That’s why any of the engines I used it in looked filthy. Maybe it was just doing what it was designed to do. Just think about all that sludge could have been in your engine oil pan.

While it may look clear and the dirt has settled out, the oil has been damaged by heat and friction. It no longer has the lubricating qualities your engine needs. The recyclers re refine the old stuff, not just filter it.

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Two things happen to oil in the engine, it collects dirt and slowly breaks down. The clear looking oil is depleted of detergents (they’re bound up with the dirt in that black layer), and is still somewhat broken down. So no, it’s not as good as new.



What you saw was the used oil sit long enough for the contamination to phase separate out of the used oil.

When oil is new, it has additive packages such as detergents, friction modifiers, and anti-foaming agents.

Once the oil is used, those additive packages have been used up.


Good grief . . . I’ve been hearing people talk smack about Pennzoil for years

But I’ve never personally known anybody that suffered any kind of engine damage whatsoever from using it

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I only got 200K with my diesel using it and after that quit using it even in my lawn mower. My gas Olds before that needed rocker arm pivots at 240K, Like I said, every engine that I got to see the inside of was coated and not clean like other oils and after frequent oil changes. Can’t say that it caused damage for sure but I sure didn’t like what I saw inside the engines. With Mobil, even after 300K and 500K, I never had any rings sticking or rocker pivots wearing out. Years before that my BIL questioned why I used that stuff but I never listened to him.

If you’ve ever poked around Bob’s The Oil Guy, you’d find that Pennzoil is pretty highly regarded over there. Especially their synthetic Platinum line. I use Pennzoil Platinum almost exclusively for my daily driver.

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I don’t know if the newer Pennzoil yellow bottle is better but wouldn’t have an issue with their Platinum line. Yes, engines with the yellow bottle in the past would always be cruddy. I don’t know about now but I got several changes of Mobil 1 in the 5 quart jugs for $12 each so that is about as cheap as you can get for a quality synthetic oil. I have been using this and still have several in reserve.

Motor oils 25% additives, and these get used up as you drive. That’s one of the main reasons for changing it. When the dirt settles to the bottom, you have a very inadequate oil remaining on top, devoid of many necessary additives!!!

I’d say @auto-owner is doing a pretty good job of changing oil. You got the oil warm and circulated, the oil suspended all that garbage and it got drained away. JUST as it is supposed to do. The residual oil, as the others have pointed out, has the additives all used up. No way I’d put that back in anything.

I have. But not in 40 years. Pensoil and QuakerState oils had a lot of problems when gas companies switched to unleaded. The engines ran a lot hotter and many oils broke down and turned to sludge. But haven’t heard anything since the reformulated.

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I think some of the Pennzoil/Quaker State issues from the '70s on back resulted from them using Pennsylvania crude. Not much of that around any more, they now use the same oils as everyone else.

In addition to the cautions posted by the other forum members, I want to add that motor oil has a tendency to turn acidic over time, especially if it has been used in an engine that is subjected to a lot of short trips with not enough opportunity to get up to full operating temperature.

As others said, that oil is only fit for recycling at this point. :-1:

If you want to be sure of this, you would have to send a sample to a lab for a used oil analysis. While that separated oil wouldn’t be like new, it might have spare lubricating capacity.

Having said that, I wouldn’t use it in my engines.

Whatever settled to the bottom were elements heavier than the based oil. Only an oil analysis can tell you what they are for sure.

There’s no way I’d use used oil in my engine. When I do an oil change, I’m removing used oil… why would I put used oil back in?

Seriously, the additives that allow viscosity to be less susceptible to heat (“viscosity modifiers”) may be in that sludge rather than suspended in the “clear” oil where they’ll do some good, and the “clear” oil you want to reuse may be freed of additives that prevent corrosion.

If you have the sludge analyzed, post back. I’m curious to see what it’s comprised of.

NOTE: if you know someone studying chemistry (your son? yourself?), they can separate used oil exactly the same way with a centrifuge, a basic tool that every chemistry lab has.

Recycled motor oil s nothing new, filter it put in new additives and it is good to go. As far as old oil in the bucket a no go for me. It is the additives that get depleted, and are most needed as far as I know.

NextGen never did much in the market. Probably because it was used oil being sold for virgin oil prices (often higher). At that point, there’s no compelling reason to just not buy the standard non-recycled Valvoline.

Anything within the last 10 years . . . ?!

Nope. Probably around 1988 was the last I used the stuff. Might be fine now but I’ve moved on. Once burned and all that. That’s why my general opinion on branding is that once you ruin it, you are better off to dump it completely and start over with a new one. People always make the mistake of hanging on to a troubled brand because they had so much invested in it but really it’s sunk money. Others on my list are Craftsman, Kelvinator, etc. that I think are turning into boat anchors. Who wants to wait a couple generations to revitalize a damaged brand? I still avoid Holiday gas because of the 60’s when the Erickson brothers had Erickson/Holiday stations with a lot of water in it.

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