Mazda says run 5W20 oil. I live in hot NC and I am wondering if there's any problem using Castrol 5W30 at my first oil change? I just got my silver RX8 and love it. 200 miles on odomoter and I plan to change the oil at 800 miles, then go 3000 thereafter. Why wouldn't Mazda specify a slightly heavier oil for the RX8? Seems too thin to me?? Any enlightenment greatly appreciated.

 

i believe the main reason is emissions, and the second is that the light oil will still do just fine in nearly any driving condition on the street... have you seen those oil coolers???

 

Personally I would use 10w30 and will use that when/if I get my car next spring. Afaik, the European manual recommends 10w30. The only reason 5w20 is recommended in North America is because of CAFE. Last time I checked the Renesis is the exactly same engine internally here and in Europe.. Up to you if you want to worry about the warranty issue.

 

I think someone on this forum said the J-spec manual listed SJ 5w30. There is only a small difference in high temp high shear (HTHS) viscosity for 5w20 at 2.6 compared to 2.9 - 3.1 for typical 10w30 and 5w30s. This viscosity measurement is important for rotor gears and housing injection. My main concern is Mazda may be changing the ECU programming for the oil injectors in different world markets. You won't get as much 5w30 injected at high oil temps if the US/Canada cars are calibrated for 5w20

 

Honestly I doubt that. I think most of the piston cars have also started to recommend the 5w20 in North America. Same engines as last year, different oil. Same engines in Europe, very different oil requirements there, usually 5W/10W-40. It's all about the CAFE, imo.

 

I hope you are right too but engineers are perverse and they have lots of data-comm and processing built into the 8 so I can see the possibilities

My pet theory is euro piston oil specs try to reduce consumption at high speeds. If I'm right then engine protection is only better because oil stays in longer. This is where the 20w50 thing got started with 4 bangers on the autoroutes. A Pennzoil rep once told me that 5w30 protected bearings better than 20w50 in their testing!

There used to be a saying "Germans shift up when the car won't go any faster and Italians shift when the valves bounce!!!

 

That could be true because the 5w30 will flow easier due to being "thinner" at operating temps. I really doubt that Mazda would program the ECU differently for North America over the rest of the world. Like I've said before, I'm not a "rotohead" so I don't know exactly how the 20 weight oil will affect the rotary engine or how hard the engine is on the oil at 9,000rpm but I would not be very confident with a 20 weight oil in my current car at a lapping event when my engine is at 6-8K rpm all day.

Once again, not sure how "hard" the rotary is but I will use at least a 30 weight in my car, probably synthetic too.

 

Correct! 10W30 is fine. 5W20 is used to improve fuel economy.

 

I'm with ya there. On my ol' '79, the manual recommends 20w50 for temperatures above 0 Centigrade, and I can't imagine that a 5w20 oil will take the abuse of Solo I or II events in 30 Centigrade heat.