Engine Oil Myth Or Fact?

[Sl!m]

these might be helpfull for you as well

http://www.skylinesaustralia.com/forums/in...=113560&hl=

http://www.skylinesaustralia.com/forums/in...=109762&hl=

http://www.skylinesaustralia.com/forums/in...c=22458&hl=

http://www.skylinesaustralia.com/forums/in...c=81764&hl=

http://www.skylinesaustralia.com/forums/in...=115490&hl=

[Busky2k]

If you have a 10W40 synthetic and a 10W40 mineral, they are the same thickness. Anyone who tells you synthetics are too thin should be slapped.

[EVIL TWIN]

Um, eh?

The first number (before the W) indicates the oil viscosity when cold.

The second number indicates its viscosity when hot.

So mobil 1 5W50 viscosity is 105 centistokes at 40 degrees C & 17.5 centistokes at 100 degrees C. 0W40 equivalent numbers are 80 & 14. The hot end is more important because you can cook the oil in a GT-R quite easilly with no cooler. This is why a higher viscosity hot temperature property can be a good thing.

These are physical properties of the oil & don't refer to it's protection. For that you need look at different API ratings for the oils. I don't know what "the amount of protection - ie the protection of a 50W oil." means.

Try the Mobil website....

http://www.mobil.com/Australia-English/LCW...c_V_Mineral.asp

Is that you Richard?

How can the second number indicate the viscosity when hot? If that were the case, you're saying the viscosity becomes higher when it gets hot, ie it becomes thicker when it gets hot.

I'm pretty sure oil becomes less viscous when it's hot.

"the protection of a 50W oil" simply means a higher level of wear protection.

I may have confused the explanation, as I was just regurgetating what was written on the back of an oil container.

What I meant was a 5W50 is thinner than a 10W40 but offers higher protection from wear.

[Trust33]

im using and have been using,Castrol Sport 5w30,for the past 2 oil changes.the bottle has the grey label on it.Its a top oil.this oil is fully synthetic and was designed to run in older model sports cars specifically skylines etc.

I was running penrite semi synthetic oil before.that to was pretty good.but not as good as the castrol full syn....It will be the first test at the track this month with this oil.its had a thrash at EC skid pan and wsid.now to hit the track and see how it performs.

[Trust33]

"the protection of a 50W oil" simply means a higher level of wear protection.I may have confused the explanation, as I was just regurgetating what was written on the back of an oil container.What I meant was a 5W50 is thinner than a 10W40 but offers higher protection from wear

Thats why earlier on in the thread it was stated that the oil with the higher rating,for running hot "viscosity", is used at the track where the car cops a continual flogging.

And the lower rating is used for the street.

Ie: a higher rating is impractical for the street,as it will not offer the full protection of the 40w (which heats up quicker).simply because if there were a 60w in there it wouldnt be using the full thermal properties that a higher viscosity rating oil will offer thus the oil would be thicker,in turn inhibiting movement of rotating parts with the thicker oil.which could prolly lead to damage at an extreme.

Thats why synthetic oil rules over mineral.because of it's thermal properties and also its purity.

Correct me if im wrong here.

[djr81]

Is that you Richard?

How can the second number indicate the viscosity when hot? If that were the case, you're saying the viscosity becomes higher when it gets hot, ie it becomes thicker when it gets hot.

I'm pretty sure oil becomes less viscous when it's hot.

"the protection of a 50W oil" simply means a higher level of wear protection.

I may have confused the explanation, as I was just regurgetating what was written on the back of an oil container.

What I meant was a 5W50 is thinner than a 10W40 but offers higher protection from wear.

Yeah, thats me.

Not saying that at all.

There are two numbers. The winter number is on the LHS before the W & the summer number is on the RHS. That the RHS number is larger is not indicative of the viscosity being higher than the winter number. Almost all liguids lose viscosity as they get hotter, oil not least.

Please don't confuse viscosity with wear protection. They are not necessarily related.

[djr81]

Thats why earlier on in the thread it was stated that the oil with the higher rating,for running hot "viscosity", is used at the track where the car cops a continual flogging.

And the lower rating is used for the street.

Ie: a higher rating is impractical for the street,as it will not offer the full protection of the 40w (which heats up quicker).simply because if there were a 60w in there it wouldnt be using the full thermal properties that a higher viscosity rating oil will offer thus the oil would be thicker,in turn inhibiting movement of rotating parts with the thicker oil.which could prolly lead to damage at an extreme.

Thats why synthetic oil rules over mineral.because of it's thermal properties and also its purity.

Correct me if im wrong here.

Um, ok your wrong.

Oil does not jump from one viscosity to the next. It varies continuously with temperature (inversely as mentioned earlier). The difference between a (for example) 0W50 oil & a 5W40 oil at normal operating temps will be next to stuff all.

The viscosity of the oil is not indicative of its protective properties, but is indicative of its film thickness (to a degree). That a thicker oil is necessarily better is one of the enduring myths of motoring.

A higher viscosity oil will create more pumping losses within the motor - this is one reason car manufacturers are progressively lowered their oil viscosity ranges over the years.

The specific heat of the oil (ie how much energy is required to heat a certain amount a degree) is not strongly a function of viscosity. So a 40W oil doesn't heat any more quickly or slowly than a 60W oil. It will, however, be of a lower viscosity at any given temperature.

The viscosity rating is not indicative of an oil's ability to maintain its integrity at high tenperature.

[Trust33]

The viscosity rating is not indicative of an oil's ability to maintain its integrity at high tenperature.

ahh kthn.

I thought that if the oil had a start temp rating of say 5W and a hot running rateing of 60W that the oil was good at cold start up and was able to flow more oil giving the parts good oil when needed.

And so what your saying is,that if the oil was say in a hot engine being thrashed,the 40W will maintain it's hot oils integrity the same as the 50W would be able to maintain itself under polognged use.

The average street car is never going to see that sort of abuse.

The viscosity of the oil is not indicative of its protective properties, but is indicative of its film thickness (to a degree). That a thicker oil is necessarily better is one of the enduring myths of motoring.

Thermal properties of the oil are directly related to the oils viscosity because temp will thin it out IE:The molecular structure of the oil is adversly changed when heated close to boiling.so it does have an affect.

Thats where wear and tear come into play.when the oil chosen for the engine is below or above the cars natural running viscosity.u choose the oil for what abuse you intend to have the engine put under.

[siksII]

put simply, all the first number means is that the oil can be pumped through your engine in as cold conditions as a single grade oil of the same first rating can be pumped.

the second number is the viscosity at 100degress, so a xW-30 is the same as a single grade 30 oil at 100degrees.

i dont really understand what your trying to say with the thrashing vs protection examples but both of those thickness ratings have little to do with protection.

you need an oil that provides flow that the engine was designed for at operating temperature so the second number is really what matters.

breakdown at high temperature and protection from metal to metal contact cannot be judged from the two numbers.. some thin oils offer better protection at high temperatures than thicker oils.

read these sites

http://www.vwtrendsweb.com/tech/0304vwt_sy...oils/index.html

http://www.bobistheoilguy.com/

u can see the protection they offer from the charts with their specifications.