Why does engine oil degrade?

Brian Reay · 2019-02-17T12:43:59+00:00

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.

Feb 17, 2019 26 Replies

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Peter Hill 7 years ago

It's to deceive the eye and present a faux fastback coupe glass line on a hatchback / wagon.

The last two (3 door only in 2004) also had faux fastback style with rear quarter windows that tapered to the rear so the glass area looked like a fastback while the roofline doesn't drop to match. This allows a cheap hatch instead of a liftback to be fitted. Unlike proper fastback rear window which stays clean and doesn't even get wet when moving the rear window will get just as mucky as any other estate / station wagon. What the huge rear pillars on these does for rear vision when parking I can only imagine. The 2004 3 door really wasn't worth Jezza eating his own hair over.

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johannes 7 years ago

I noticed that this new faux astra design has resulted in a rather pointed edge when you open the read door. I wouldn't like to be hit by that pointed edge when somebody opens the rear door.

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Brian Reay 7 years ago

I'm curious, you seem to have an interest in car design. Are you a student studying the subject?

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johannes 7 years ago

Nope, I'm a common end end end car user. But I've always had a fascination with cars. Not happy if I don't know one new car from another. Sometimes I look at ebay classic cars section; amazed how much some old cars can fetch. Sometimes only the ghost of a car is left over, but it still fetches high prices.

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Dave Plowman (News) 7 years ago

You do have to be careful thinking a winning bid on Ebay actually buys the car. Lots and lots of timewasters bid for cars on Ebay. Both on the buying and selling sides. Lots trying to make a fast buck because they think there is a classic car boom.

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Brian Reay 7 years ago

I fear, with the various new rules on emissions etc, classic cars will be a thing of the past (no pun intended). I traded in an immaculate

1999 MX5 in Nov 2018 under one of the scrappage schemes- I got around 4x book value- it wouldn't have been allowed in the London ULZ (at least without a huge fee) or in some of the places we go in France and need a Crit'Air for.

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