Why does Mobil1 recommend different oil viscosity for fully synthetic oil than for semi synthetic? 1

[rcx194]

I'm going to use Mobil 1 and Suzuki Sidekick / Vitara as an example. This is an old 1990's car. When I used to look up the recommended engine oil on the Mobil 1 website it would come up with semi synthetic 10W40 and fully synthetic 0W40 options (the site no longer recommends any oil for my car for some reason).

Why did the site recommend a different viscosity for the fully synthetic option?

For older cars, 1980-2000s, where the factory manual was written in pre-synthetic days, can I buy fully synthetic oil in the viscosity recommended in the manual? Or does the viscosity change when using fully synthetic?

Thank you.

 

[TugboatEng]

You'll always be ok running the viscosity recommended by the manufacturer, synthetic or not.

The advantage of synthetic oils is that they have either better viscosity index and/or better wear protection. Therefore, a lower viscosity oil can be substituted while maintaining the same high temperature performance and wear protection. This allows the same oil viscosity to be utilized over a wider temperature range. It also reduces friction losses some but the difference is not likely to be noticed on a single vehicle.

 

[SuperSalad]

What Tug said.

To add to that and to address your specific website portion of the question (I was an administrator for lubricant recommendation website software). When you design the program, you group vehicles into categories based on the OEM recommendations and then assign appropriate viscosities as "comparable" or "equivalent". I am sure that for this matching, the mobil software is looking primarily at the SAE viscosity first and the winter rating second. The 0W-40 is the preferred SAE 40 that mobil wants to recommend, but since they want to offer options for customers who may not want to purchase a full synthetic, they group the closest semi-synthetic they offer as an "equivalent" since it still matches the appropriate SAE viscosity grade.

- Andrew

 

[romke]

The oils that are recommended for use in a particular vehicle primarily is based on the technical requirements of the vehicle manufacturer. The manufacturer usually specifies a number of viscosities, depending on the ambient temperature range the car will be used in. Usually you will have a number of choices there. The manufacturer also specifies a performance level for the oil to be used, for example API SN or a proprietary specification that must be met. The oil to be used thus is specified by 2 parameters: viscosity and quality. As long as you choose a product that meets both requirements suitable behaviour of the oil in the engine can be expected.

The objective requirements as chosen by the manufacturer are the starting point for the recommendations of the oil supplier. Usually a number of products are available that meet the technical requirements. Which products then are recommended is based on the marketing ideas of the oil supplier - and those can vary over different countries. Not every product will be available anywhere.

Mobil 1 is a kind of family name for a range of products. There are quite a number of varieties sold over the world that can differ quite widely in terms of specification, productcomposition, pricing etc. As long as the variety chosen meets the requirements of the car manufacturer you will be ok.

 

[LionelHutz]

You can't get 0w40 in semi-synthetic.

The manufacturer probably specifies Xw40 as the oil to use. For the most part, 0w40 is just comparatively thinner than 10w40 when cold, so using 0W40 is better for cold starts than 10W40 and has little effect at running temperature. If you want to go down a rabbit hole then start researching.

What does surprise me is the people who say their 20 year old car specified say 5W30 synthetic so they must only use that, even though the 5W30 synthetic on the shelf today is not the same as the 5W30 synthetic from 20 years ago. Not that it usually makes much difference in practice, but I find that insistence to religiously stick to the weight part of the oil without paying any attention to the actual oil spec a little comical.

 

[TugboatEng]

I am a fan of synthetic oils but I am also simple minded. I use whatever the synthetic version of what the oil cap says. If that spec is not available I'll select the next lower winter weight that is. For daily drivers it's just not worth investing any more thought.

With the introduction of 0w-16 oils I don't think the advertised viscosity means much anymore. The manufacturers are going to come up with funky grades like this to force you to use the correct synthetic oils.

 

[rcx194]

Thanks for the replies. I'm now a *little* wiser. For the record, I'm not certain that Mobile one recommended 0W40 as the fully synthetic option for my Suzuki, it may have been 0W30, but the point I was making is that the viscocity was different to what they were offering in the semi synthetic option.

It is a bit upsetting that Mobil1 have stopped recommending any oil for some of my older cars, it feels like they've just carelessly abandoned owners of older cars.

 

[3DDave]

That specification issue is a nasty one. See

https://topclassactions.com/lawsuit...auto-motor-oil-28-5m-class-action-settlement/

Of the three oils, this is the most amusing: DG SAE 30 (SA specification) for use in vehicles manufactured after 1930

Still being sold in 2010.

 

[TugboatEng]

There is one hiccup lately. The API grades typically superceed each other. For diesel oils a new API grades F is concurrent with the previous C grade. If you're engine is prior to 2017 you're supposed to run API CF-4. 2017+ runs API FA. The FA oil is 10w30 and most of the CF oils are 15w40. But there are a few 10w30 CF grades out there to make things confusing. Now we actually have to pay attention.