turbotoaster

Since i used to work for fuchs/silkolene i know a fair bit about oils, though when it came to what to run in a rotary i wasnt 100% sure, most of the tuners i spoke to had different opinions.

WGT said he would never run fully synth on any engine, even race ones, 20b, 26b etc

Reworx said use the best oil you can and dont worry, never had problems running fully on there engines.


So i thought, well im friends with the guys who actually design the oils so i may aswell ask them.

So i emailed a guy i used to work with at silkolene, nice chap who works in the labs to see what he thought.

here it is below, if you wanna ask any questions i can forward them on to him as he only lives up the road from me and my mum is his boss so hes always happy to help.

ME

Ok thanks very much.

Now im running a rotary engine at the moment, the engine has just reached its first 1000miles, this has been run on 15w50 mineral oil to bed everything in.

Now i understand the benefits of synthetic oils over mineral oils in a normal piston engine all to well.

The issue i have is that the rotary sprays through a pump some of the engine oil into the combustion chamber to lubricate the seals, bit like a 2 stroke bike

Mazda tests fully syn back in the early 90s and found that full syn did not burn cleanly and eventually left deposits in the engine.

Obviously oil technology has progresses since then and in an ideal world id block off the pump, run full syth in the engine and mix full syn 2stroke oil in with my petrol to lubricate.

Now thats 2 much of a pain really as it means ill always have to have oil in my car for that.

So im wondering what modern fully syn are like, i know bike ones are ashless but are car ones? id imagine the temps in the customer chamber are going to be much higher than the flash point on tech sheets ive seen

Lee




JOHN



Dear Lee,
All ‘synthetics’ are very definitely not the same, so which type of fully syn did Mazda test in the 90s? I bet even they don’t know!
2-stroke oils are either low ash or (rarely) ashless, meaning that they do not contain large amounts of substances containing calcium and zinc to make the oil last for 10,000 miles…..not really necessary in a 2-stroke. All 4-stroke oils are high ash, but this normally doesn’t matter because 4-strokes don’t burn much oil, so they do not accumulate zinc oxide and calcium oxide (lime) deposits in their combustion chambers. (These cause pre-ignition.)
Early rotaries such as the Norton (and the related Mid-West Aviation aero engines) ran very well on our ashless ‘Comp-2’ synthetic ester 2-stroke oil, but the Norton engine was also tested and found to be OK on high-ash monograde mineral diesel engine oil. (Much cheaper.) My feeling is that rotaries are OK with high-ash 4-stroke oils because of the high ‘G’ forces generated by the rotor; any heavy combustion-chamber deposits will be flung of by very high centrifugal forces. Of course, the road Mazda RX8 uses standard 4-stroke oil, so I am told.
All rotaries run high rotor temperatures, so any combustion chamber oil deposits should burn off easily, even with heat-resistant ester and PAO synthetics. I’d go for Pro-S 5W/30, a heat-resistant high-ester full synthetic which is less likely to form coke on the inside of the rotor and ruin the needle roller bearings.
Don’t worry about flash point. (All to do with safety in storage.) Engines have been running combustion chamber temps way above oil flash points since about 1890. (Seriously!) Flash point is the temperature at which the oil vapour rising off a static pool of oil can be ignited in air when exposed to a flame. It is NOT the same thing as spontaneous ignition temperature, which for all oils is around 400-450C.
Yours sincerely, JR


Now i havent mentioned to him about the use of my car: ie big boost, big power etc so im gonna come onto that next with him.

My car now has 15w50 pro r fully syth running through it, due to the expected high heat it will have to deal with and the chance of fuel blowby into the oil.
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