Why does engine oil degrade?

I've always been someone who changes their engine oil (and filter etc) regularly. In the days of mineral oils, every 5/6k miles or 6mths, with synthetic oils, 10/12k / 12mths, assuming the vehicle wasn't spec'd for less.

I've a friend you swears he never changes his oil and has, or had (I've not seen him for awhile) an ancient lorry (an HGV) which he insists he'd never changed the oil in, just topped it up. Admittedly, it was only used for perhaps 6 or 7 mths of the year and even then covered only a few 1000 miles, if that. (He was a showman with a ride who traveled and set it up at various events.)

I've looked at several videos on YouTube covering DIY recycling of oil, essentially filtering it to remove the 'larger' bits, then leaving the rest to settle, after which (supposedly), you are left with 'clean', almost clear as original, oil.

While I am prepared to accept this may remove the solids, any other dissolved 'gunge' will still be they, plus if the oil has changed in structure/natured, it isn't as it was.

I'm not remotely thinking of reusing engine oil, the hassle isn't worth it, but I am curious.

Some further reading has shown that oil is recycled on a commercial scale by being broken down (fractioning) in a way not unlike how crude oil is processed. However, this is a complex process, with quality checks etc.

Reply to
Brian Reay
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Engine oil contains a lot of additives. Detergents, to keep carbon particles in suspension. Old oil is black because of the stuff in suspension, which won't really settle. The detergents eventually get "used up" by bonding to the particulate. Viscosity improvers give you the 10-50 performance, or whatever. These are long chain molecules which gradually break down and become less effective. Anti oxidants help stop the oil from oxidising, these get used up. Corrosion inhibitors which get used up. Maybe anti-wear additives, which get used up.

I wouldn't be surprised if old oils are treated by filtering and then going through something very like a refining process, as you suggest.

In some industrial environments which are mostly much less "aggressive" than an IC engine the oil charge may last for decades, although it will be regularly checked. If properties (such as rust prevention) decline, the oil will be "spiked" with a suitable additive package.

Reply to
newshound

That makes (mainly) makes sense - although I?m not sure why particles in suspension don?t settle out (it is long time since I studied such things). Older oils ( in terms of technology) could possibly have been more readily reused due to their not having all the additives originally.

I assume, from what you say, it is the presence of viscosity improvers which make multi grade oils possible.

Reply to
Brian Reay

Google "Brownian motion"

Correct

Reply to
newshound

Thank you, I've done some reading / revision. Brownian Motion does keep some particles in suspension but only above a certain size. The sizes are truly tiny, so there will still be some settling. I assume, if you cool the oil (therefore reducing the Brownian Motion), you could increase the settling out rate. Probably not practical etc, at least in the amateur scale.

Reply to
Brian Reay

Not only not practical, it wouldn't even work. As you cool, the viscosity and hence the settling rate reduces dramatically. If you freeze the oil it stops altogether.

Brownian motion was first observed with pollen grains in water. The smallest pollen, according to Wikipedia, is about 6 microns diameter. The diesel particulate in air pollution that people worry about is < 2.5 microns. A practical alternative to filtration would be a centrifuge, indeed I had a car once which had one for engine oil on the end of the crankshaft. Simca 1300, for the curious.

Reply to
newshound

Most old motorbike flywheels I've seen have a little plug that can be removed to clean out the centrifuged bits, but I don't think the capacity can be adequate beyond a few years. I always cleaned them out, mostly out of curiosity.

Reply to
Dan S. MacAbre

Good point. I think the argument is to catch big bits, swarf, etc. before it starts machining anything. The one in my Simca was full of white metal wear debris (very finely divided), no sign of black carbonaceous stuff.

Reply to
newshound

I only ever found hard-ish black sludge; but it makes more sense (I think) that it was really intended for the more damaging stuff.

Reply to
Dan S. MacAbre

Large IC engines - like those found on smaller ships - don't tend to have routine oil changes. Better filtration - including a centrifugal type - and analysis of the oil followed by a top up package of additives to suit.

Reply to
Dave Plowman (News)

Good point.

I remember seeing it first demonstrated at school with smoke particles.

Simca cars, there is a name from the past. If memory serves, they were absorbed by Renault.

Reply to
Brian Reay

That would have been Alpine, creators and makers of the "Frog box" aka Renault Espace.

Simca French division of Fiat. Chrysler. Finally Peugeot PSA.

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I took my first 3 driving lessons in an 1100. It had the heaviest clutch I've ever encountered, I'm convinced that some idiot dealer had fitted a double spring. Even a 4x4 Bedford SP Green Goddess has a lighter clutch. Considering it had less power than a Honda CB750 that used a one hand clutch it was an abomination. On the 3rd lesson I told the instructor what he could do with his clutch.

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Reply to
Peter Hill

We had an Espace for about 13 years. An excellent family vehicle.

In general, I don't like the style of French cars, the first two models of the Espace are the exceptions (we had the Mk2), the later ones seemed to become more 'French', although by the time we replaced ours the girls we older and we didn't really need an MPV. (Small children seem to require more 'baggage' etc. on trips.)

I vaguely recall there was a small(ish) specialist company that designed both the Espace and a 4x4 (or perhaps a 4x4 look alike) which had a hump in the roof. I thought Simca either owned it or had an interest in it and Renault either absorbed Simca or bought the design. However, I could be wrong.

There is a lot of 'wheeling and dealing' of designs, major sub-assemblies etc between (what appear to be) rival companies- as I'm sure those on the group know. A prime example is the Fiat Ducato which is (all but) identical to a couple of other vans. Not to mention, Fiat selling the engine and/or chassis/cab etc to countless motorhome builders who add their own rear ends / tops. My Rapido A class has a Fiat engine and upgraded chassis. Or previous Swift had a Ducato cab and chassis.

Reply to
Brian Reay

The previous version of Ford Ka looked similar to Fiat 500 in overall shape, do they have the same platform? I also noticed that the wedge shaped Ford Fiesta looks sinmilar in overall shape to Fiat Punto?

Reply to
johannes

I'd guess so, but the current version. I went to look at some Ka/500s for a friend looking to buy. Give or take some splashes of colour, on the inside you could be sitting in the same car.

Reply to
RJH

I would be very surprised if they have. I'm not aware of any tie up / link between Ford and Fiat in the way, for example, Ford there has been with Ford and Mazda and one of the other Japanese car makers (specifically over small SUV which Ford, essentially, seemed to have badged as far as I could tell. I can't recall the other maker- may be Toyota.

Of course a lot of cars look very similar, especially small ones. I expect it is simply a combination of design constraints, current design ideas, 'fashion', and possibly even using central (outside) design consultants and/or offices.

Reply to
Brian Reay

Second generation Ford Ka (2008-2016) was developed in conjunction with Fiat 500. They are essentially the same car.

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Therefore it wouldn't surprise me if the wedge shaped Ford Fiesta was developed in conjunction with Fiat Punto Grande, They look so similar in overall shape.

Reply to
johannes

Well, I am surprised!

Reply to
Brian Reay

Actually Fiat Grande Punto was a joint venture with general Motors. I once hired a Fiat Grande Punto, and on another occasion a Vauxhall Corsa. The key fobs were exactly the same for both cars. Both cars have flimsy parcel shelves with holders that break.

Still I think the shape of Fiat Grande Punto is like the wedge shaped Ford Fiesta.

Reply to
johannes

And CFD homing in on the optimum shape given the other constraints.

Reply to
newshound

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