This is the fourth analysis on used oil for my RX-8. The first was on the factory fill, the next two were on Pennzoil 5W-20 and this one is on Castrol Syntec Blend 10W-30. Of course, there is still something like 35% Pennzoil in this analysis left over from the last change.

I tried the Castrol because the previous analyses had all shown viscosity lower than expected for 5W-20 oil and high fuel dilution. I wanted to see if increased viscosity would have any noticeable effect on the amount of wear metals found.

I took the sample with a Vampire sample pump and did not change the oil. Reason for this is the first three changes were at 2000 mile intervals and I wanted a sample at similar mileage. I plan to run around 4000-5000 miles total on this interval before the next change.

I got the 'M' flash in mid-July so that may be helping to reduce the fuel dilution. The car just had it first birthday so the miles are piling up slowly. No flooding incidents and my long term gas mileage is 18.3 mpg.

Here are the results compared to the last change on Pennzoil:

Odom....................8027..............6018
Interval.................2009..............2014
Oil.........................Castrol...........Penn zoil
Grade...................10W-30..........5W-20
Make-up...............0.6 qt.............1 qt
Elements in ppm
Aluminum..............3....................3
Chromium.............4....................3
Iron......................15..................16
Copper.................2....................4
Lead.....................1....................2
Tin........................1....................0
Moly......................96.................240
Boron....................23.................79
Silicon...................7....................7
Calcium.................1741..............2110
Phosphorus..........755................768
Zinc.......................858................937

SUS @ 210°F........53.4...............48.5
Flashpoint............375.................355
Fuel%...................0.5..................1.5
Antifreeze%..........0.....................0
Water%................0.....................0
Insolubles%.........0.2..................TR

I got a decent increase in viscosity (SUS) although this mix is still in the 20 weight range. I wonder if shearing may not be a possibility in this engine due to the stationary gears. Fuel dilution fell off, maybe due to the 'M' flash. Otherwise the wear metals are the same within lab error.

Ok. Anticipating a couple of questions.....

Q: Why did you use a synthetic blend?
A: Just trying to **** off both the synthetic and dino camps by straddling the fence.
Q: Aren't you afraid Mazda will void your warranty?
A: Apparently not.
Q: Why not 5W-30 instead of 10W-30?
A: I live in Houston, Tejas which is just south of hell.
Q: Didn't your gas mileage go in the crapper using 30 weight oil?
A: Too soon to tell for sure but the early results say no.
Q: Why don't you use RP or Amsoil or Silkolene or .....
A: If I can't get it at WalMart it doesn't exist.

Since the Castrol does not seem to have destroyed my engine, I plan to do the next couple of changes with the Syntec Blend. After that, I may switch back to 5W-20 for a couple of changes to see if makes a difference. At this point, I don't think it will matter.

yrotory

 

If your the same person that is from Bob's site, then I have been following your thread there.

After reading how your oil was getting thinned to a 10w, I switched to 10w-30 also. It hasn't impacted the mileage at all on our 8.

 

Hmmm this make me want to find my oil Analysis sheet.....

 

Interesting study. You have less moly (wear protectant) and calcium (detergent) in the new oil. The lower gas dilution might be due to the seals seating in now. Just curious, does your oil smells gasoline at 0.5%? I know mine does at 3500 miles (got it on my fingers, and after the soap washed the oil, I can smell the gasoline). Who ran the analysis for you? I suspected high fuel dilution hence I top of the oil between changes with 10W40 to keep the viscosity acceptable.

 

The samples were analyzed by Blackstone Labs. I haven't noticed any strong gasoline smell in any of the oil samples but I don't have the most sensitive sense of smell either.

The reduced fuel dilution may just be the seals finally doing their job, the 'M' flash, or some other factor. As long as it remains low and I don't see the very low viscosity that I got on the first few samples I will be satisfied.

yrotory

 

Did they explain the big decrease in moly -- is that something that is still just trending down from the factory build-lube?

 

The drop in moly is because the Castrol Syntec Blend 10W-30 is formulated with a lot less moly than the Pennzoil 5W-20.

yrotory

 

Civilian, here. I just wanted to weigh in to say that I find this discussion fascinating. I'm using Pennzoil 5W-20 myself. Thanks for going to the effort, yrotary.

 

Interesting....

I've been running Royal Purple 5W-20 (full synthetic) since new. I have 17,200 miles on the odometer, and have no ill effects. Would it be possible to send an oil sample to you for analysis? I'm sure there are plenty of folks on this site who would be interested, and perhaps we could put the "is synthetic okay" debate to rest.

 

Tony,

I would love to see a few more used oil analyses (UOA) for the RX-8 run on different oils. Its the only way to learn anything that isn't just anecdotal.

There are several companies that do used oil analysis and the cost is fairly low. Blackstone Labs has done all mine at $20 each. If you go to their website you can sign up for them to send you the sample kit free. Fill the bottle, mail it back, and your report shows up a few days later.

I'm sure other companies have similar arrangements.

yrotory

 

Sweet, thanks.