Engine Oil

It's a long story. The standard grading of oil goes back to the 1920's, the viscosity behaviour was compared to a standard, e.g. grade 15 is a light oil and grade 50 is a heavy oil. People used to change oil according to climate and season. A fixed grade oil had a large viscosity variation with temperature. That made cold starting difficult. Then multi-grade additives came along to reduce the variation of viscosity with temperature.

A 5W40 oil behaves as grade 5 at zero degree C, and behaves as grade 40 at 100 deg C. Some people mistakenly call it "multi-viscosity"; but that is a complete misnomer. The correct term is: "multi-grade", which in a sense is the complete opposite to "multi-viscosity".

The answer is to use the oil you can afford of the recommended rating and change it at least as often as the book says you should.

That's the sort of question Google is good at answering.

& so the right one is recommended in your cars manual :-) Summer & winter use isn't really an issue in the uk

Thanks to multigrade... But there are other issues. A large grade span means more additives in the oil. Additives wear off, so an extreme multigrade doesn't last as well as a narrow multigrade. Commercial vehicles which are driven all day may be better off with a narrow grade range; if cold starts are rare.

Really? All these extended life oils have a wide viscosity span - and a life of anything up to 20000 miles. Not much point in having extended service intervals if the oil can't cope with the seasons.

Yes indeed, johannes is spot on with his explanation.

Julian.

According to whom? If cold starts are rare only the higher number is relevant & the oil is mainly affected by blow by.

But it's the other way around! You start with a single grade oil, e.g. a grade 10 oil. That oil will be far too thin viscosity when heated to engine operating temperatures. Then multigrade additives are added. The additives starts working at higher temperatures, making the oil e.g. grade 40 at 100 dec C.

Good point, but I'm still of the opinion that you gain sod all by using a narrower range oil, breakdown of the viscosity enhancers was never raised as an issue when we where destruction testing engines.

OK, there may be different quality of additives, but everything being equal... E.g. a bus running all day in a tropical country will rarely need a cold start, hence a narrow grade range, or even a fixed grade is ok. Chances are that the oil will keep thicker for longer.

Full synthetic are supposed be superior as they don't have additives to wear off. The oil is formulated from scratch. Mobil 1 is supposed to be about the best.

But you'll still want to change it before then anyway. It's like worrying that the tyre rubber next to the cords is harder & doesn't grip the road well.

Thanks for all the comments. I think I should have made my question shorter and simpler.

My car I believe is recommended for 5W30, 5W40, 10W30 10W40.

I think they put some crap cheap oil in last time. I don't have the paperwork with the info on but I do remember it was semi-synth.

I should have really done an oil change sooner but I've left it pretty much the full 18,000 miles. It's almost 2 years since it was changed last so I think this time I will choose the oil myself and shelve out for some fully synthetic and one of the more expensive types. Maybe Amsoil, Xado or I think someone mentioned Mobil1 was quite good.

I think I get the first part of the number. Lower is better for colder starts right? Cause my car don't start good in the cold. I think they must have put 10W in last time maybe.

Okay, a simpler question...

I think I understand the first number before the W, but the second would 0W40 mean that it is also better at higher temperatures as well as low temperatures? So it would be grade 40 at 100°c? That means its thicker at 100°c than 0W30 and so that's better?

So a 0W40 would be better at higher and lower temperatures than say a

0W30? And maybe 0W40 also would give better fuel consumption? Am I thinking this right or have I got it completely wrong? Is one better for performance with the narrower gap and the other better for fuel economy or something? Or is it simply to do with the time of year e.g. summer and winter use?

I believe I should be okay putting 0Wxx in my car shouldn't I? It's just whether to go with 0W30 or 0W40 now to decide.

I do a lot of short journeys and I've heard that ester based oils are bad for shorter journeys so I should avoid brands like Motul and X-Lite for my car use and find something that's based on PAO?

I don't have the foggiest what PAO stands for but that's what I read somewhere else. I also don't have a clue whether Amsoil and Xado are ester or pao type oils?

I think Mobil1 and Shell Helix are pao though aren't they? If anyone can clarify what pao means and what type Xado and Amsoil are that ud be great.

Ta

John

Well for starters it depends on what the car is. Given the only people who bother to test oils across a range of conditions are the engine manufacturers it's normally far more worthwhile looking at what they say than most of the hearsay on the subject.

At 18,000 miles you have probably spent £3000 on fuel, so the cost of an oil change (+filter) shouldn't break the bank.

I do it myself because I'm a paranoid suspicious person; how do you know which kind of oil a service station is putting in your engine? Some service stations don't even remove the oil plug, they just suck up the old engine oil.

Depends what is required for your car. Seems odd that both W30 and W40 is specified. Maybe there are different engine variants for your car and you need to find out more details about your car, not just the cc.

All cars take varying oil viscosities , it depends on the ambient temperature of the country you are in , colder means the first figure is lower , hotter means the first figure is higher

Perhaps, but it is not optimal. A car with tighter tolerances on the oil seals may use a W30 rather than a W40, it depends on the construction of the engine.