Whats difference between semi synthetic and full synthetic

[HardDriver]

Hi guys. As you can see of this post topic, I want to now differences between these oils? What benefits have semi and what full? What about longevity? Is it true, that synthetic oil is designed with improved lubricate properties and enhanced viscosity to provide superior protection from engine wear, reduced heat breakdown volatility for decreased oil consumption, improved fuel mileage, easier engine cold starting and a reduction in engine deposits.

What minuses have semi? How long could you use this oil (when did he change his structure)? Is it true, fully synthetic oils are not really necessary unless you have a high-powered sports/luxury car or an engine with significant performance upgrades (highly tuned). Obviously engines that are subject to high stress levels (like supercars or motorsport machines) need the best protection available, so it makes sense to splash out for the finest oil. But the majority of road going cars are not highly stressed or severely punished on a regular basis, so semi-synthetic is more than adequate. One more thing, I heard also, that they are same, but interval (when they change structure) for fully is longer, for semi not?

Is it true, that fully synthetic have lighter viscosity (slippy ) (if I take both 10w40) and semi harder?

Thanks for comments. I need to change my oil and I don't know what should I use?


Also, I need to change gear oil, it's SAE85w90 or SAE90w90. Isn't these oils rare? What should I use? Can I use not recommended oil? Will be really bad?

[Fisty]

Not sure if serious.
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[MarJay]

Have you just copied the blurb from the back of an oil bottle into BCF?
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[Chalky.]

Semi synthetic is equivalent to half of a full synthetic.

Sometimes it is better to run the engine at double the normal level with semi synth. I've run engines half full with fully synthetic too though to save money - cost of oil halves.

[HardDriver]

[HardDriver]

[Fisty]

[Tamsin]

Semi-Syth is 50% mineral oil (i.e what they drill out of the ground) and 50% synthesised in a lab.

Synthetic is totally manufactured - none of that stuff they drill out.

as to what to put in your bike and when to change it? RTFM

[mentalboy]

[HardDriver]

Yeagh, I know that, thanks for posts. If someone knows answers for my questions, please tell me. Ignorance killing me .

[Kickstart]

Hi

My understanding is that oil itself doesn't wear out, rather the additive packages do. Synthetic oils need less additives to get a wide viscosity range. Hence less of the bit that wears out and they last longer.

But still full of the rubbish that gets last the rings, etc.

All the best

Keith
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[lihp]

[Teflon-Mike]

[Tamsin]

[weasley]

So much waffle in one post.

An engine oil is made of base oils and additives. The base oils are the major part, comprising around 80-ish percent of the formulation (give or take, depending on the specific needs). The overal description "mineral", or "synthetic" etc refers only to the source of the base oils. The remaining 20% is a mix of additives to enhance or modify the performance of the base oils. The additives can be natural or synthetic, and are usually diluted in mineral base oil to make them easy to handle.

The term "semi-synthetic" has no specific basis in law or any other regulation. It refers to an oil with a mixture of some part mineral oil and some part synthetic. It does not have to be (and is rarely) 50:50. It could be as low as 20% or as high as 80% synthetic. Other terms like "part-synthetic" or "synthetic-enhanced" are also common.

In general terms, the higher the % of synthetic, the higher the overall performance. Using better base oil can also mean you don't have to add as much additive.

Mineral oil is refined from crude oil, from where it is distilled and then impurities extracted by solvent washing and other treatments.

Synthetic oil is either:

1. Taken from crude oil, as above, but then treated in a hydrocracker to chemically alter the molecules to eliminate unhelpful ones and create good ones

2. Synthesised from scratch using ethylene gas molecules as a building block to make long chain molecules. The gas comes from the refinery by the way, so this came out of the ground too. This type is known as polyalphaolefin, or PAO.

3. Other types are made by chemical reactions, such as esters and polyglycols.

An oil "wears out" though a number of mechanisms. Some additives become exhausted in use as they do their job, meaning you have to change the oil to refresh them. The base oils do get affected too, by oxidation, which causes them to polymerise and get thicker, as well as forming acidic species which can be corrosive. The viscosity-controlling polymers added to oil also get broken up by shearing effects, which reduces their effect and causes the oil to thin out at high temperatures. Finally, the oil collects contamination as it goes along which eventually reaches a level that the oil can't hold and needs to be changed. Some of the oil 'boils' away in the engine too, which is generally why the level drops over time and you need to top up. Remember, topping up is good not only to get the level of oil up but also because it adds a shot of fresh additives.

Also, crude oil can look anything from treacle to black water, depending where you get it.
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[arry]

It gets further complicate by some synthetic oils not actually being fully synthetic but a hydrocracked semi

The main advantage as I understand it is that ester oils are much more resistant to shear which means they can handle more abuse in respect of high temperature

[weasley]

[arry]

Interesting, thanks.

Are the likes of Silkolene Pro S fully ester or just part ester?

[Polarbear]

[weasley]

[Pete.]

Semi synthetic will always beat fully synthetic in a scrap. Fully synthetic just ain't got the minerals...
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