A quick guide to the different oil grades

[Spôôk]

Never change "down".
If your car has been running on fully synthetic for 3 years - DO NOT change "down" to semi - etc.
Spôôk

[Keith]

Spook did you mean to post this twice?
I have merged the thread but will leave it to you to delete one or the other duplicate posts

note, some of your text is white on white :)

[MartinW]

Sorry, but I disagree with many of the comments in the table - these are not attributable simply to the viscosity grade, they are more to do with the base stock performance and additive formulation.

However, I agree, once settled with an oil choice, stick with it! And likewise, don't switch to synth from semi or mineral on a high mile engine.

And these days a full synth can be called that despite being a mineral oil. It's a legal issue based around performance, and Grp 3 mineral oils are highly refined and hydro-treated - so you pay your money and you get your quality.

[crofts]

Sorry, but I disagree with many of the comments in the table - these are not attributable simply to the viscosity grade, they are more to do with the base stock performance and additive formulation.

However, I agree, once settled with an oil choice, stick with it! And likewise, don't switch to synth from semi or mineral on a high mile engine.

And these days a full synth can be called that despite being a mineral oil. It's a legal issue based around performance, and Grp 3 mineral oils are highly refined and hydro-treated - so you pay your money and you get your quality.

Hi Martin
If that is true then it's pretty misleading in my opinion. How can a mineral oil be called synthetic. That's confusing. Did they decide that in Strasbourg ?
( the place of straight bananas, cheddar cheese and melton mobray pies)

[MartinW]

The decision was made in the US, and Chevron were one of the main proponents for calling it synthetic. Their arguement is that the Grp 4 PAOs synthetics are based on product derived originally from crude oil, and therefore Grp 3 is hydro-cracked and thus synthetised to achieve a similar level of performance.

Synthetic is a broad term relating to man made, and usually implies identical molecular structure to have predictable and superior performance compared to mineral oils.

The biggest con is semi-synthetic as there is no regulation on what quantity of synthetic and mineral must be present.

[Dave Goody]

Sorry, but I disagree with many of the comments in the table - these are not attributable simply to the viscosity grade, they are more to do with the base stock performance and additive formulation.

However, I agree, once settled with an oil choice, stick with it! And likewise, don't switch to synth from semi or mineral on a high mile engine.

And these days a full synth can be called that despite being a mineral oil. It's a legal issue based around performance, and Grp 3 mineral oils are highly refined and hydro-treated - so you pay your money and you get your quality.

Agree totally, I was a lubricants manager for one of the major oil companies years ago, and used to persuade haulage companies that by buying engine oil in bulk tanks 1200 lts + they could buy quality high detergent lubricants for diesel lorries at the same price per litre as cheap oil in barrels.
On a high mileage truck, the high detergent oil we sold would clean the gum out of the engines caused by the cheap sometimes monograde oils, causing the most ominous rattles and sometimes dire consequences. We learnt quickly and only advised the use of these high quality oils for new or nearly new vehicles.
People should remember synthetic products have to be made from something and most will be made of something originally mineral or organic.
Unless imported from Mars? :lol: Dave