The reasons synthetic oils are better

[oilman]

I thought this would be of interest as It\'s probably the question I get asked the most. Shame the answer isn\'t simple though!

The basic benefits are as follows:

Extended oil drain periods
Better wear protection and therefore extended engine life
Most synthetics give better MPG
They flow better when cold and are more thermally stable when hot
Esters are surface-active meaning a thin layer of oil on the surfaces at all times

If you want to know the reasons why then please read on but, warning - Long Post!

Stable Basestocks

Synthetic oils are designed from pure, uniform synthetic basestocks, they contain no contaminants or unstable molecules which are prone to thermal and oxidative break down.

Because of their uniform molecular structure, synthetic lubricants operate with less internal and external friction than petroleum oils which have a non-uniform molecular structure.

The result is better heat control, and less heat means less stress to the lubricant.

Higher Percentage of Basestock

Synthetic oils contain a higher percentage of lubricant basestock than petroleum oils do.

This is because multi-viscosity oils need a great deal of pour point depressant and viscosity improvers to operate as a multigrade.
The basestocks actually do most of the lubricating. More basestocks mean a longer oil life.

Additives Used Up More Slowly

Petroleum basestocks are much more prone to oxidation than synthetic oils. Oxidation inhibitors are needed in greater quantities in petroleum oils as they are used up more quickly.

Synthetic oils do oxidize, but at a much slower rate therefore, oxidation inhibiting additives are used up more slowly.

Synthetic oils provide for better ring seal than petroleum oils do. This minimizes blow-by and reduces contamination by combustion by-products. As a result, corrosion inhibiting additives have less work to do and will last much longer in a synthetic oil.

Excellent Heat Tolerance

Synthetics are simply more tolerant to extreme heat than petroleum oils are. When heat builds up within an engine, petroleum oils quickly begin to burn off. They are more volatile. The lighter molecules within petroleum oils turn to gas and what\'s left are the large molecules that are harder to pump.

Synthetics have far more resistance as they are more thermally stable to begin with and can take higher temperatures for longer periods without losing viscosity.

Heat Reduction

One of the major factors affecting engine life is component wear and/or failure, which is often the result of high temperature operation. The uniformly smooth molecular structure of synthetic oils gives them a much lower coefficient friction (they slip more easily over one another causing less friction) than petroleum oils.

Less friction means less heat and heat is a major contributor to engine component wear and failure, synthetic oils significantly reduce these two detrimental effects.

Since each molecule in a synthetic oil is of uniform size, each is equally likely to touch a component surface at any given time, thus moving a certain amount of heat into the oil stream and away from the component. This makes synthetic oils far superior heat transfer agents than conventional petroleum oils.

Greater Film Strength

Petroleum motor oils have very low film strength in comparison to synthetics. The film strength of a lubricant refers to it\'s ability to maintain a film of lubricant between two objects when extreme pressure and heat are applied.

Synthetic oils will typically have a film strength of 5 to 10 times higher than petroleum oils of comparable viscosity.

Even though heavier weight oils typically have higher film strength than lighter weight oils, an sae 30 or 40 synthetic will typically have a higher film strength than an sae 50 or sae 60 petroleum oil.

A lighter grade synthetic can still maintain proper lubricity and reduce the chance of metal to metal contact. This means that you can use oils that provide far better fuel efficiency and cold weather protection without sacrificing engine protection under high temperature, high load conditions. Obviously, this is a big plus, because you can greatly reduce both cold temperature start-up wear and high temperature/high load engine wear using a low viscosity oil.

Engine Deposit Reduction

Petroleum oils tend to leave sludge, varnish and deposits behind after thermal and oxidative break down. They\'re better than they used to be, but it still occurs.

Deposit build-up leads to a significant reduction in engine performance and engine life as well as increasing the chance of costly repairs.
Synthetic oils have far superior thermal and oxidative stability and they leave engines virtually varnish, deposit and sludge-free.

Better Cold Temperature Fluidity

Synthetic oils do not contain the paraffins or other waxes which dramatically thicken petroleum oils during cold weather. As a result, they tend to flow much better during cold temperature starts and begin lubricating an engine almost immediately. This leads to significant engine wear reduction, and, therefore, longer engine life.

Improved Fuel Economy

Because of their uniform molecular structure, synthetic oils are tremendous friction reducers. Less friction leads to increased fuel economy and improved engine performance.

This means that more energy released from the combustion process can be transferred directly to the wheels due to the lower friction. Acceleration is more responsive and more powerful, using less fuel in the process.

In a petroleum oil, lighter molecules tend to boil off easily, leaving behind much heavier molecules which are difficult to pump. The engine loses more energy pumping these heavy molecules than if it were pumping lighter ones.

Synthetics are better and in many ways, they are basically better by design as they are created by chemists in laboratories for a specific purpose.

Cheers
Simon

[AndyGen3]

Thats a good read! Opened my eyes!!!

What Synthetic oil wud u advise to use?

[oilman]

5w-40, the best are the likes of the Motul 300v and the Silkolene Pro S.

Cheers

Simon.

[Jake]

Great post, very informative.  I\'m running fully a synthetic oil in my Rex after reading one of your previous posts on true synthetic oils.  Thanks for the info.  :Thumbsup!

[Jake]

Just been looking at your site, mainly the Motul area as I\'ve used their 5.1 brake fluid and found it to be excellent.  What gear oils would you recommend for a 3rd Gen RX-7?

I\'ve also been looking at the \'Inugel Optimal\'.  Am I understanding this correctly that you use this in your radiator instead of water and anti-freeze?  Would it be fine to use in a 3rd gen?

[Smifta]

Jake,

I use Sylkeline Syn 5 in both my gearbox and diff (on Oilman\'s recommendation). I have extremely happy with it in both the RX and the MX5.

Alex.

[M@r]{]

I hear what you are saying, almost persuaded me but....

I hear a lot of people talking about the fact the RX is designed to burn oil (similar to a 2 stroke?)  but synthetic oil by design will leave a desposit when burnt - which is bad in a rotary engine?  Bad to have deposits in the chamber? (ive heard Royal Purple doesnt but the cost of that over a few years would amount to a rebuild!! )  Im not knowledgable in this subject, this is just what ive heard mentioned so cant say it is accurate, only mentioning it so I can be put right if I am wrong - I would feel better using snthetic particlualry because of the high oil temps I seem to get.  

One thing though:
 
WGT have said my rebuild warranty is void if I use synthetic!

[LRP]

this is interesting ive always been told to use mineral oil i use the same stuff they put in the rx8??

[Jake]

Cheers Smifta, I\'ll have a look at it.

I actually use Royal Purple in my Rex since before Christmas after reading around for ages about oils and the whole synthetic argument.  Oilman did a post about true synthetics a while ago that was brilliant if you haven\'t read it, would be worth doing a search for.

Here we go:

http://www.mazdarotaryclub.com/forums/showthread.php?t=10025&highlight=synthetic+oil

[Rixio]

I use Mineral aswell

[andrewrx7]

{\']I hear what you are saying, almost persuaded me but....

I hear a lot of people talking about the fact the RX is designed to burn oil (similar to a 2 stroke?)  but synthetic oil by design will leave a desposit when burnt - which is bad in a rotary engine?  Bad to have deposits in the chamber? (ive heard Royal Purple doesnt but the cost of that over a few years would amount to a rebuild!! )  Im not knowledgable in this subject, this is just what ive heard mentioned so cant say it is accurate, only mentioning it so I can be put right if I am wrong - I would feel better using snthetic particlualry because of the high oil temps I seem to get.  

One thing though:
 
WGT have said my rebuild warranty is void if I use synthetic!

Does the oil actually get burnt, or just vaporised? There is a difference. If you think about the reason why the oil is there in the first place, it is for lubrication of the seals, so the less burnt it gets, the better the lubrication. Perhaps synthetics with their higher temp stability help lubrication in this manner - vaporising rather than burning? I don\'t know - could be wrong!

I know the RP cost is said tounge-in-cheek, but really, an oil change with RP is less than a tank of petrol! It may be twice the cost of a good mineral, but a couple of tenners extra over 3 or 4000miles pales into insignificance compared to the fuel costs!

But lets be honest, who has any real issues with either proper synths or minerals? Has anyone actually ran multiple, identical engines apart from the oil, side by side for 50 or 100k miles, then stripped them down to evaluate differences? Errrr.....don\'t think so! Just carry on using the mineral that Pip recommends to safeguard the warrenty, then when it has expired, re-evaluate the oil at that point in time!

[kev-yorks]

this is interesting ive always been told to use mineral oil i use the same stuff they put in the rx8??

Total Oil supply oil to some of the Mazda dealerships and as we service there trailers i asked them what they use in the RX8. Guesss what its a full synthetic quartz 9000 that Ford also use in the Zetec engine.
Kevin :3gears-rh

[Fish]

Subaru had the same issue as Ford a few years back, swapped to Silkolene and it cured the issue for a little while until they re-designed the part that kept breaking.

The design from the 7 to the 8 may well have improved, but remember the 7 works on OLD oil deisgn!

Fish

[fraser]

But lets be honest, who has any real issues with either proper synths or minerals? Has anyone actually ran multiple, identical engines apart from the oil, side by side for 50 or 100k miles, then stripped them down to evaluate differences? Errrr.....don\'t think so! Just carry on using the mineral that Pip recommends to safeguard the warrenty, then when it has expired, re-evaluate the oil at that point in time!

Yes some has done this and they don\'t recommend synthetics!  They\'re called Mazda, and people seem to ignore the vast amount of testing that went on to develop the engine.  Sorry oil man, good sales pitch, but I\'m not sold.....  (And my PHD was in gearbox development, largely focusing on wear and lubrication).

As for the new advice on the RX8, the wear characteristics and carbon adhesion properties of ceramics are vastly different to metals, and therefore the bear little relevance to and RX7.

Regards

Fraser

[oilman]

{\']I hear what you are saying, almost persuaded me but....

I hear a lot of people talking about the fact the RX is designed to burn oil (similar to a 2 stroke?)  but synthetic oil by design will leave a desposit when burnt - which is bad in a rotary engine?  Bad to have deposits in the chamber? (ive heard Royal Purple doesnt but the cost of that over a few years would amount to a rebuild!! )  Im not knowledgable in this subject, this is just what ive heard mentioned so cant say it is accurate, only mentioning it so I can be put right if I am wrong - I would feel better using snthetic particlualry because of the high oil temps I seem to get.  

One thing though:
 
WGT have said my rebuild warranty is void if I use synthetic!

This is a misconception, synthetic oils in fact burn more cleanly and leave less deposits than their petroleum conterparts.

Cheers
Simon