Which engine oil?

[marcus]

I'm planning an oil change for my 1985 1.8 GTL (carburettor EX engine) and Haynes says use 15 or 20W50 but everywhere I look I see 10W40 recommended, is this grade ok for my engine?

BTW, Euro Car Parts have a 30% off engine oil promo on at the mo'.

[ianaudia4]

I always use VW Synta Silver, generally costs less than the stuff sold in factors!
I always use a genuine VW oil filter, costs about 3 quid from the dealers.

[wasted]

10W40 Quantum for me. It's good stuff.

[Nate]

10w40 or 15w40 mineral or semi-synthetic to vw spec 501.01 or is it 500.01, can't remember.

fully synthetic oils should not be used.

[McMad]

10w40 or 15w40 mineral or semi-synthetic to vw spec 501.01 or is it 500.01, can't remember.

fully synthetic oils should not be used.

Why do you say that full synthetic should not be used?

John

[Nate]

i don't, volkswagen do ;) it isn't the right stuff, simple as. synthetic oil was designed for modern engines, not old engines. it is prone to make older engines leak and/or burn oil. very very very common mistake that lots of people make, but more expensive doesn't mean better!

[McMad]

Synthetic oil is one of the best lubrication solutions that is currently available however you are right to point out that it may not be the "best" oil for a "high miler"

Engines leak oil because gaskets and seals become brittle and crack, shrink or loose their elasticity and ability to "seal". Because synthetic oil is generally "thinner" it is very good at getting through very small gaps which makes it a good lubricant but hard to keep inside the engine. Also there is some debate about older seal material being degraded by synthetic oil - my view is that a 20 year old oil seal is probably not in very good shape anyway so the argument is academic (modern seals do not have this problem). Non synthetic oil will oxidise and tends to fill small gaps with "varnish" (the brown gunge that coats the inside of an engine) which tends to offset the effect of seal wear somewhat. Synthetic does a very good job of removing this "varnish" and its often the case that when treated to a some nice new (expensive) synthetic oil, a previously oil tight engine starts leaking like a sieve.

Engines burn oil because the pistons, rings and bores wear allowing oil into the combustion chamber and burning gas down the side of the pistons. The oil burns and produces carbon which again tends to fill up the "gaps". Synthetic oil is very good at not burning so much and is also reasonably good at removing the cabon.

The moral of the story is that if your "old girl" has some miles on and you are a steady driver and would like a few more miles out of her before an engine rebuild, ordinary multigrade is probably best. Clean and "fresh" are the guide lines.

If your engine has had a recent rebuild and everthing is up to spec. and you like hard driving then full synthetic is the way to go. Less friction, more power and less wear - whats not to like?
Note - on a rebuilt engine you MUST break it in on non synthtic oil for about 1000/1500 miles to bed things in.

I think the "mistake" which you refer to is to blame the oil when in fact the "problems" associated with the use of sythetic oils stem from an old and worn engine.

Sorry this goes on a bit but I think that its important to understand this point.

John

[Nate]

Synthetic oil is one of the best lubrication solutions that is currently available however you are right to point out that it may not be the "best" oil for a "high miler"

Engines leak oil because gaskets and seals become brittle and crack, shrink or loose their elasticity and ability to "seal". Because synthetic oil is generally "thinner" it is very good at getting through very small gaps which makes it a good lubricant but hard to keep inside the engine. Also there is some debate about older seal material being degraded by synthetic oil - my view is that a 20 year old oil seal is probably not in very good shape anyway so the argument is academic (modern seals do not have this problem). Non synthetic oil will oxidise and tends to fill small gaps with "varnish" (the brown gunge that coats the inside of an engine) which tends to offset the effect of seal wear somewhat. Synthetic does a very good job of removing this "varnish" and its often the case that when treated to a some nice new (expensive) synthetic oil, a previously oil tight engine starts leaking like a sieve.

Engines burn oil because the pistons, rings and bores wear allowing oil into the combustion chamber and burning gas down the side of the pistons. The oil burns and produces carbon which again tends to fill up the "gaps". Synthetic oil is very good at not burning so much and is also reasonably good at removing the cabon.

The moral of the story is that if your "old girl" has some miles on and you are a steady driver and would like a few more miles out of her before an engine rebuild, ordinary multigrade is probably best. Clean and "fresh" are the guide lines.

If your engine has had a recent rebuild and everthing is up to spec. and you like hard driving then full synthetic is the way to go. Less friction, more power and less wear - whats not to like?
Note - on a rebuilt engine you MUST break it in on non synthtic oil for about 1000/1500 miles to bed things in.

I think the "mistake" which you refer to is to blame the oil when in fact the "problems" associated with the use of sythetic oils stem from an old and worn engine.

Sorry this goes on a bit but I think that its important to understand this point.

John

erm, how does a putting incorrect oil in give you more power?

[marcus]

Less friction. Friction results in heat. Heat is the product of energy being wasted. No doubt a physicist could provide a more accurate description but that's the general idea.

[Nate]

but the level of lubrication the oil provides is defined by the grade of the oil (10w40 type thing) not by whether it is a mineral oil or a synthetic oil.

[marcus]

But aren't the fully synthetic oils thinner, because their physical properties allow them to be made thinner while still providing the same level of protection?

[Nate]

a 10w40 fully synthetic oil won't be any thinner than a 10w40 semi synthetic or a 10w40 mineral oil. i ain't no chemist, but the main reason that synthetic oils are used in modern engines (and despite what you may think, rocco engines ain't modern engines!) is to do with how the oil behaves as it gets older and the residues that are left when it gets burnt.

manufacturers spend millions designing engines, and select oils for it to give the best performance in a given situation (look inside your owners manual, and you'll see a chart listing the oils to be used for different operating conditions) now bearing in mind synthetic oil has been around longer than these engines have (they were the only lubrication used before "mineral oil" [i.e. oil derived from petroleum] was discovered/invented about 120 years ago) so had their boffins figured that synthetic oil was the way forward, they would have specified it. and of course they would have if they could even slightly justify it, it's way more expensive! but no, they decided that semisynth was correct.

at the end of the day, you can put whatever the speedboat you like into it, and to be honest, i don't really care. fill it with 5w20* fully synthetic and while you're at it put some nice g12* into the cooling system, and top up the brake fluid with some dot5*. it'll give me a good giggle when it breaks down next week :)













*these fluids are not the correct ones for your vehicle, and will make it break