Voilà une info qui je pense donne à réfléchir provenant du site Rotaryrevs.com (http://rotaryrevs.com/garage/help/rotar ... l-for-rx8/)
"5w30 = Too Thin to Maintain Oil Pressure
VISCOSITY
As mentioned above, rotary engines traditionally have always been run on a 10w40 or 15w40 grade mineral oil, especially in the UK.
As we understand it, the RX-8 engine code, 13b MSP, was designed no differently than the RX-7 engine codes before it (13b REW’s, RE’s, DEI’s) and so we assume that Mazda technicians had every intention of using the same grade of oil in the MSP as they had used previously in the RX-7. So why the change in recommended grade of oil to use?
Well, in 2002 ‘Total’ sold Mazda the concept of achieving better fuel economy by using a thinner grade engine oil. Mazda responded by introducing 5w30 across their entire range of cars, and a lot of other car manufactures at the time quickly followed suit. It is true that using a thinner grade oil will cause less drag in the engine and in turn, unlock a little extra horsepower and slightly improve fuel economy – at an almost un-measurable rate in terms of the day-to-day running of a rotary engine it must be said!) It is also true that many modern day, highly tuned, piston engines must be run on thinner and thinner engine oils as well.
It wasn’t until the RX-8 owners had started to break through the 50,000 mile benchmark that rotary specialists (such as ourselves), started to notice the problems that the thinner grade oils and low oil pressures were causing in the Renisis engines.
Stationary Gear Bearing Failure was fast becoming a phrase synonymous with RX-8 engine failure among enthusiasts and specialists alike. We see it all too often at Rotary Revs and in fact, every single RX-8 engine that we have ever stripped down (regardless of mileage) has shown some level of wear on the stationary gear hydrostatic bearings.
This is why we insist on switching to 10w40 engine oil, to help counteract this issue and hopefully extend the life of your engine and protect those gear bearings.
To summarise:
Your RX-8 Renesis engine needs oil to lubricate it’s bearings. This is important in order to avoid the harmful build-up of ash and carbon which can cause rotor apex seals and side seals to stick.
The thinner grade oil recommended by Mazda (5w30) is too thin for the oil pump inside the RX-8 to maintain the oil pressure necessary in an idle state, at low revs per minute (RPM). So, for this reason we enforce a strict 10w40 oil policy on all cars we work on, to help reduce the wear of the Stationary Gear Bearings, thus extending the life of your engine.
Rotary Revs thoroughly recommends draining, completely, and changing your oil at least, once every 12,000 miles or per annum; ideally changing at every 3,000 – 6,000 miles, topping up whenever necessary."