Tough low-ash engine oil specs
 

As I prepare for the end of my car's rotary core warranty -- and for a fresh engine at 75k miles -- I've been doing some research and thinking along the lines of this thread. This seems important because it's so hard to find an oil known to excel in wear control, deposit control, and catalytic converter friendliness all at the same time. An advantage in one of those areas usually comes with a weakness in another, but all are important for a cat-equipped rotary engine.

In addition to the ACEA specs mentioned in that thread, there are more and more OE specs that require low ash levels but still have equal or tougher performance requirements vs. their higher-ash counterparts. For illustration purposes, here are some comparisons using Lubrizol's Relative Performance Comparison Tool -- not exactly surgically precise, but good enough for ballpark work.

Mercedes-Benz 229.52 and 229.71 (both low ash) vs. MB 229.5 (spec for AMG cars):

https://cimg5.ibsrv.net/gimg/www.rx8...5278f9d208.jpg

VW 504/507 (low ash) vs. VW 502/505 (good enough for the Audi R8 and any of VAG's semi-modern turbo gas engines):

https://cimg9.ibsrv.net/gimg/www.rx8...17102eae6c.jpg


Real world example, with a rightly popular high-performance synthetic oil:

- Mobil 1 0w-40 meets MB 229.5 with 1.34% ash by ASTM D874
- Mobil 1 ESP Formula 5w-30 meets MB 229.51 with 0.6% ash
- Mobil 1 ESP X1 0w-30 meets MB 229.52 with 0.8% ash

In other words, the ESP oils clear the same performance bar as Mobil 1 0w-40, at least as far as MB is concerned -- but they do it with 44% to 59% less ash.

This comparison isn't definitive because it only reflects the minimum requirements; a lower-ash oil might just barely meet them while a higher-ash one might meet them with room to spare. However, Mazda only specced API SL/SM for these engines, which any of these oils should absolutely crush performance-wise.

Cost notwithstanding (they're expensive!), I wonder if oils meeting these low-ash specs might be worth considering for anyone who wants to run a really tough oil while preserving their cat. They might be the best available combination of wear control, deposit control, and cat friendliness.

Thoughts?

M1 is good stuff, try the ESP and then test it and see.

But none of it will mean anything in terms of making a Renesis more reliable.

I agree - Wally World oil and Tractor Supply oil - both SAE SN grade 5W30 are less than 1% ash
API Service Classification SAE 5W-20, 5w-30 & SAE 10w-30 SM, ILSAC GF-5 Resource Conserving
SAE 10w-40, SAE 20w-50
SAE 20w-20, SAE 30, SAE 40 SN
Always consult owner’s manual for proper grade to use.
Physical Properties

SAE Grade
5W-20
5W-30
10W-30
10W-40
Viscosity @ 40ºC
51.81
67.80
69.17
110.3
Viscosity @ 100ºC
8.870
11.09
10.55
15.71
Viscosity Index
151
156
140
151
CCS cP @ (ºC)
5457(-30)
6262(-30)
5919(-25)
6257(-25)
API Gravity
33.15
32.79
31.15
30.80
Sulfated Ash, %
<1.0
<1.0
<1.0
<1.0
Performance Level
API SM/G

I've read some posts of yours along these lines in other threads. Is your opinion that differences among decent engine oils are insignificant next to the engineering and build quality factors?

Yes it is. I used to think "cheaper" oils may have led to excessive bearing wear, etc. but after participating in a few tear downs, I now believe that most of the engines are just not balanced or assembled correctly and that overall the Renesis is just a poor design in terms of longevity, more so when seeking power.

But I still use Mobil1 0W-40 in mine and change it every 3k at least. But mainly just because I want it to be as clean as possible when I have to rebuild it, :lol:

Fair enough. That'd be in line with what tends to be the case for piston engines as well, AFAIK.

That's kind of why I'm interested in these low-ash options though. If performance reserves beyond the API SL/SM level are insignificant, why not focus on minimizing deposits and keeping the cat healthy?