As long as oil meets the spec the engine manufacturer specifies I doubt it matters a jot to most drivers what brand of can it comes in. The worst oil you can buy today is probably ten times as good as the best oil from 40 years ago and people still managed to make engines outlast the rest of the car back then.
The Tesco 5w/30 I saw the other week isn't just cheap because it's a crappy old spec mineral oil, it's a semi-synthetic to API SL spec made by Tetrosyl designed specifically for engines like my Zetec and would normally be three or four times the price. I assume they're still making a profit at £5 for 4 litres but god knows how. I bought a car load of it and once the special offer is over I'll knock it out on Gumtree or Ebay for £10 or £15 a can.
Maybe a fully synthetic API SN spec oil costing £10 a litre or more is better still but how long does anyone need their engine to last? Not much point in trying to make it last twice as long as the chassis before that rusts away.
Back in about 1990 when synthetics were fairly new and Mobil 1 the best known of these I knew someone who worked in an oil test lab. They'd dyno engines for specified periods under set loads and measure components to microns before and after to test for wear. Even back then they were getting no detectable engine wear over the test period with Mobil 1. I really wonder just how much better the very latest oils are and whether we even really need them unless you're aiming for 500,000 mile engine life.
The other thing about modern engines is they don't tend to wear much in the first place unless you really abuse them and it's the swarf from initial wear that causes a chain reaction into terminal wear. Old engines like the CVH and to a lesser extent the Pinto had cams that wore out like buggery at the best of times because they weren't properly designed. It made little difference what oil you had in there because it would be full of microscopic metal particles anyway. By 70k to 100k miles the rest of the engine would be completely shagged. I regularly used to see 5 thou or more bore wear on even medium mileage CVH donor engines I was rebuilding into race motors. I once measured 8 thou on a 70k mile CVH engine. Modern chill cast cams in twin cam OHC engines just don't wear and create swarf and then nor do the bores or crank bearings wear either. Modern low tension thin piston rings also create much less bore wear than old style thick rings.
I can strip down 100k mile modern engines and still see the cross hatching in the bores. Having to get cranks reground is almost a thing of the past too. I'd say that it's valve guides and stem seals that go before anything else in most engines. Mainly engines with cheap grades of bronze valve guides which the continentals are very fond of for some reason and which only lasts a fraction of the life of cast iron and sintered guides. Peugeot, Citreon, BMW, VW and others often use crappy grades of manganese bronze for valve guides whereas the Japs and Ford tend to stick with ferrous guides. I've never even seen a really shagged iron valve guide in a Ford CVH even when the rest of the engine was toast. However the manganese bronze guides in VW Golf or Peugeot 205 engines often wouldn't last a single race season with high lift cams.
In most modern engines though the main largish metal bits last for ever. I suspect they would still last for ever no matter what oil you put in there.
The Zetec engine in my Focus has everything in it spot on for minimum wear. Iron guides, chill cast cams with light valve springs and thin piston rings. They just don't wear out - period. As long as it has oil in it of some sort or other, to the max mark on the stick and not too black and manky I couldn't care less what make it is. It'll outlast me.
Absolutely spot-on! I'm glad somebody with verifiable credentials has posted that (not that many will listen).
There's so much drivel talked on Internet forums about engine oil you'd think chosing the wrong brand or API rating would cause your engine to grenade itself within 6 months.
A lot of folk on forums seem to talk about engine oil selection like it's a black art and hysteria abounds.
Pumaracing's last paragraph, in particular, sums it up perfectly. People should concern themselves more with changing their oil and filter regularly.
The only time I think it's somewhat warranted to pay very careful attention to engine oil selection is when racing or anywhere that a flat tappet cam is in the mix. I run a solid flat tappet cam with heavy springs in the 500bhp 383 SBC in my Cobra replica and I use a particular brand of oil (at considerable expense) because it has an additive package specifically tailored to cater for the special needs of flat tappet cams.
It's a shame that more gifted engineers like pumaracing don't post much... I've spoken to a few and they all say 'what's the point?' All the arm chair experts know best... everyone knows that!