Results for my the oil analyses on my RX-8 are listed in the attached file. They are listed from most recent to oldest. The two most recent samples are Castrol Syntec Blend 10W-30 and are both for the same interval, in other words the oil was not changed between samples. I used a sample pump to get the samples. The next two samples were on Pennzoil 5W-20 and the first sample was on the Mazda factory fill.

In spite of the oil being about 65% 10W-30 with the rest 5W-20, Blackstone found the viscosity to be in the lower 20 weight range. I plan to change the oil this weekend with another interval on the Castrol to see if the viscosity picks up any. Also, the M flash seems to have stopped the earlier problems I had with high fuel dilution. This oil has been in service about 6 months so I had a TBN run which read 4.6. This indicates plenty of active additive. I have added almost 2 quarts of make-up oil during the 4000 mile interval.

As a quick guide, Al, Cr, Fe, Cu, Pb, Sn, and Ni are wear metals, the rest are part of the additive pack. High silicon can indicate poor air filtration and high sodium and potassium can indicate a slight coolant leak.

yrotory

 

Interesting...
Thanks for the write up

 

Nothing real bad showing and dilution looks real good. Two questions, why are you running non recommended oil viscosity and is your car stock?
The high initial silicon is probably from left in the engine from casting and not bad filtration.
Thanks and keep the reports coming!

Vince

 

The car is bone stock. I've only been back to the dealer for the M flash and the recalls. No CAI, exhaust, etc. The air filter is original and oil filters have all been the Mazda teacups which seem to be doing a fine job.

I went to the 10W-30 oil because the first three analyses had viscosity ranging from 46-48 SUS @ 210°F. This is down in the 10 weight range. It was at least partly due to fuel dilution. The current analysis is still low end 20 weight. The viscosity should increase some with the next change.

The Castrol spec sheet for 10W-30 Syntec Blend shows a virgin viscosity of 62 SUS @ 210°F. I would like to get up closer to that for an interval or two. Afterwards, I will switch back to 5W-20 for a few intervals to see if there is any noticeable difference.

Based on the analyses I can't say there is a compelling reason not to use 5W-20, but at the same time the 10W-30 seems safe to run.

yrotory

 

What was your history of fuel dilution (I wish that BL put that on the chart)?

Also any added oil?

Vince

 

Here is my sixth sample:

https://www.rx8club.com/series-i-tech-garage-22/sixth-oil-sample-45081/

Vince

 

Vince.....Fuel dilution was between 1.5% and 2% for the first three samples, 0.5 for the fourth, and <0.5 for the most recent sample.

I have added oil for all of the intervals except the first one where I wanted to get a sample of the factory oil only. Oil consumption has been running about 0.5 qt per 1000 miles and I typically add some oil about every 1000 miles. This interval includes 1.8 quarts of make-up oil.

yrotory

 

I wonder if the "M" flash had something to do with the dilution going down? Anyway, thanks for the data!!

Vince