engine oil and viscosity

[landybehr]

Hi,

maybe it´s been discussed severeal times - but if so I missed that

Well, I keep reading that the V8 should not have a synthetic oil because it is to thin.

I do not quite understand that. Every oil is rated in it´s viscosity. Like SAE30 or whatever. 15W40 gives a hint to the temperature range within which the oil can retain a certain viscosity. And I think that one of the numbers from 15W40 tell us the "native-viscosity" i.e. the viscosity the oil would have without additives, in this case the "15W" and by adding molecules that change their form and grow in size if temperature rises the oil can keep this viscosity if hot; the level up to which this works is the second number. If I misinterpreted something so far please correct me.

Ok, considering the above why should it matter if an oil is mineral, semi- oder synthetic. Doesn´t Synthetic say that the basic stuff of the oil is better brand or not mixed with lesser carbon molecules ? Maybe the additives are superior.

In a nutshell - to my interpretation it wouldn´t matter if you used a 10W40 mineral oil or a 10W60 synthetic. The latter just is much superior in pressure resistance, etc.

The viscosity IMHO should represent a objective value and provide comparability. Like the temperature - 0deg is just 0deg whether in Arctis or Sahara.

I once contacted 2 or 3 oil manufacturers with this question (a 4.6V8 taken as an example) and got the answer that, corresponding to what you read above there are no real arguments against a synthetic (other than cost and maybe on old engines it could dissolve&take debris with it which would better remain in the oil channels.

I am asking because I just happend to read something opposite in the archive.

[Ryan]

I'm not an oil techie, but I believe the only thing that indicates the viscosity is the 15w40 etc number. The 15w indicates how it performs on start-up i.e. cold engine (IIRC w = winter...), the second number is its performance at temperature. I think the problem with mineral v sythetic is that normally, mineral oil can only have a certain range. To get a wider range i.e. good cold start and good hot temperature performance, you have to go for synthetic as it is easier to manufacture the performance into it. AFAIK a mineral based 15w40 is the same viscosity as a synthetic 15w40. What additives there are is usually down to the individual producer (cleaners, anti-carbon thingie etc).

That said, I would always put in what the manufacurer says - they usually give you a range of viscosities to chose from depending on the climate you live in.

But like I said, I'm not an oil techie

[q-rover]

There is no difference in viscosity between a 10W-40 synth or mineral.

They are both made from long dead dinosaurs.

The difference is that mineral oil comes from sludge that is left over, synthetic

oil is highly refined, clean and has been manipulated to perform very well.

It also probably has a greater number of detergents and other additives.

The viscosity is indicated as 10W-40 in a multigrade oil.

10W(inter) being its relative viscosity at a temp of 40C.

The 40 being its relative viscosity at a temp of 100C.

So the lower the first number, the more like water it is at cold start.

The higher the number at the end the more like treacle it is in your warm engine.

[Ryan]

Phew! I wasn't far off then...

[landybehr]

Ok,

so I have not been wrong.

But for what technical reason statements like this exist:

"Use only Classic high detergent style Oils such as 'Castrol Magnatec' or 'GTX', do not use fully synthetic or oil additives"

(been taken from the website of one of the well known V8 specialists. But that message is not unique from him).

I can understand that changing from mineral to synthetic on a well used and worn engine is not a good idea.

But why synthetic oils are "banned" from the use in a V8 is beyond me.

[bill van snorkle]

There is no difference in viscosity between a 10W-40 synth or mineral.

They are both made from long dead dinosaurs.

I'm going a bit off topic I know, but is that really where oil comes from ? When an animal, Dinosaur or otherwise dies, it invariably lies above ground and is either consumed by other animals or decays away to nothing but dried up bones. Where does the oil come from?

Bill.

[Paul Wightman]

Synthetics have far more efficient detergents so if put into a V8 (unless rebuilt or new) will dislodge the cornflakes and carbon buildup and sh@g the engine very qiuckly. Eenv to the point of blocking the pickup strainer!

[landybehr]

Haven´t you heard of the Undertakerus Rex ??

I'm going a bit off topic I know, but is that really where oil comes from ? When an animal, Dinosaur or otherwise dies, it invariably lies above ground and is either consumed by other animals or decays away to nothing but dried up bones. Where does the oil come from?

Bill.

[jeremy996]

I'm going a bit off topic I know, but is that really where oil comes from ? When an animal, Dinosaur or otherwise dies, it invariably lies above ground and is either consumed by other animals or decays away to nothing but dried up bones. Where does the oil come from?

Bill.

Trying desperately to remember my long dead Geology A Level and degree in Environmental Science, most oil is decayed and pressure modified plant and shellfish remains. These are spread quite widely amongst sedimentary beds and gradually migrate by pressure, influenced by the rock bandings to areas within the final rock strata that act as a reservoir. Think of oil as liquid coal - coal cannot move from the beds it was formed into, oil can flow, (ooze may be a better word).

Most oil companies spend millions on recognising the likely strata for an oil reservoir to form - only drilling will confirm it. (Take all of this with a pinch of salt, I have been an accountant since 1984!)

[FridgeFreezer]

You might find this a useful reference: The Engine Oil Bible