INFO ONLY - Sulfated Ash % of popular oils
 

I did some legwork calling various manufacturers about the sulfated ash content % in their motor oils since the majority of the brands we use do not list it publicly. This number is of particular interest to rotary owners since our motors actively burn oil(OMP intact) and the sulfated ash(gum/carbon) that is created from burning the oil residue will potentially gum up the seals/plugs/etc. This is not the only factor for carbon/gum build up, but a major contributor.

This is not an oil debate. This is just a list of a single piece of data that I personally found useful, so I wanted to pass it along. Make your own conclusions. The percentages below are Sulfated Ash content by weight %, ASTM test D874.

Royal Purple:
1.39% - HPS 20w50
1.45% - HPS 10w40
.95-1.0% - Standard 20w50

Castrol GTX
.98-1.0% - 20w50

Amsoil:
1.43% - Premium 20w50
1.10% - Z-ROD 20w50

Redline:
1.2% - 20w50

Mobil1
1.21% - 15w50

I posted this in the first gen section since I own a first gen and these weights are typical of a summer driven first gen.

Next time try 5W20 :) Free horsepower and 12As can't make enough power/rev hard enough to have oiling issues.

Thanks for doing the legwork for that. I'm actually surprised that they gave you that information to begin with.

No problem on the leg work. The ash content was always a question in my head since rotaries suffer from such bad carbon/deposit build up, so I figured I would get some hard numbers.

Everyone was more than willing to get the numbers for me. That being said, the Royal Purple rep was extremely helpful and even knowledgeable about rotary engines and the build up.

i know nothing about oils so is the higher the number the better or worse?

At a very high level, the sulfated ash content is the % weight of deposits(carbon,deposits,etc) left behind after the oil has been completely burned. This website dives deeper into the sulfated ash test, ASTM D874.

Essentially the oil is burned and cooled, treated with sulfuric acid, burned then cooled again. After this process it is tested for how much sulfated ash(residue,carbon,deposits) is left behind in the oil to potentially gum up seals, turbos, etc.

All of the oil I've listed are all run by members of this forum with great success, this thread is strictly informational because I found these numbers interesting and useful.

tl;dr - Typically the lower the sufated ash content the better because less material is being left un-burnt to gum things up. There are also a lot of other factors at play in different types of oil, so take this information with a grain of salt, strictly educational.

I've just been using 10w30. The coldest temps I start it in is 20-30F and aside from a few weeks out of the year it doesn't get much above 85F. I've been on the track a few times with it though, should I be running something different?