^ Any reason you don't use 20W50 in the summer and switch to something like 5W30 in the winter?

Steve,
All my opinion only:


The weather here can go from 29 degrees to 80 during the day. Or 19 degrees to 58 like it did last week. I feel the oil warms very quickly even in those temps. My oil temp comes up and stabilizes faster than the coolant temp in fact.

I like using the old Mazda oil recommendations for RX7 before environmental concerns, valid or not, (not up for debate here, please) became the primary driver of manufacturer recommendations. That oil viscosity guide is still the same in some countries, even for rx8 from what some have posted, I think from Australia. 20w 50 spans my ambient temps the best.

The stationary gears are the prime source of iron slough off in oil analysis I think. At high rpm, they are under stress, and non-hardened gears like in the older models would crack after even one overrev (7krpm redline). So, there is load there. EP type loads. I just feel the thicker oil keeps those gears happier.

The bearings for the rotors are huge, and have the same running clearance they have always had in Mazda rotaries. I like the cushioning effect present in a thicker oil.

The engines are prone to oil dilution, which changes the viscosity sometimes rather quickly. Fuel dilution goes up in the winter, I don't like the idea of starting out with a thin oil and then
further diluting it due to outside temp fuel enrichment.

The main reason cited to go to thinner oil is cold starts, which I think for some engines may be valid, but I also think the premise is overrated. the flow is slower, but the oil film left from the last run is thicker, and less drains off the parts during cool down. I have seen this myself, and the difference in "drain off" is actually pretty significant from one oil grade and even brand to another. I think this is an aspect of cold starts that is left out of consideration, and could be significant.

I had consistent wear metals in my samples, even with more fuel dilution, and many more sub 40 degree and even sub 30 degree starts. This car stays outside so it sees it all. So I don't see a reason to change viscosity. One concern I do have is filter bypass at cold start, so I use the s2 filter only.

Well, I'd imagine oil has long evolved since RX-7 days, which is what, 20~40 years ago?

Also, fuel dilution? My oil never smelled like fuel. My summer oil sample showed very little fuel in the oil. My winter oil still doesn't smell like gas.

We don't drive a 1.5T Civic or CR-V, LOL.

Sure, agreed, some things with oil have changed and some things haven't.
Dilution also comes from premix oil if you are doing that. I know its controversial, but I think it happens to a greater or lesser extent in all Mazda rotaries.

So for the xW40 usage crowd, what should the target and range of viscosity be for new oil AND for used oil at the point of changing for critical RX8 systems that require lubrication?

oil analysis I’ve done on my 04 RX-8
 

I think you need 15 posts before you can place documents.

Another GTX 20W50 oil test, this one about 3700 miles. Comments welcome.
https://cimg0.ibsrv.net/gimg/www.rx8...372a031ba5.jpg

I just quit telling people to run 20W50 because it was a guaranteed knucklehead argument ... if you’re racing/track it’s a no brainer, but most ignore that even.

Team,

Yep. Back in the old days 20w50 was the racer's friend. Now just the mention of it makes people do and say all kinds of things.I remember Kendall Nitro70 also!

I like the 20w50 results in this engine, in my personal usage. I am happy to see low chrome, as I think that is a housing wear component, so the premix, OMP system rates and oil type seem to be working.

This sample had many more full throttle accel events, long runs through gears, holding high rpm, etc. as I was working on some air filter ideas, plus got into more than a few "test" runs involving other willing motorists.

Wow! Nitro70 is still available!

Viscosity 32(!) at 100 degress Celsius.

HTHS over 5, which is probably rated extremely conservatively.

2300-2600 ppm ZDDP!

Wow. It must really work in some applications if they are still making it.

I like the results, but if you use something with a ton of ZDDP then you probably also don't have a cat in place.

Was the car tracked?

For clarification:

The high ZDDP was for an oil that I don't use but mentioned in my post to Team, Kendall Nitro70, which I brought up for nostalgia reasons only.

I use GTX20w50 which is SN and seems to have below normal levels of ZDDP, even for SN, per the Blackstone report.

I do not use a cat. I use a lot of 2 stroke oil though, both Sohn OMP and premix.

I do not track this car.

The car was owned previously by Smutterbutter, whose homebuilt engine I am currently running. (he has a build thread).

So the engine is modded, yes?

There was a Shinka I test drove for another member(northzone) a year or so back. The owner got his engine rebuilt and it supposed was modded to run higher oil pressure, as well as SOHN among other things. So is your oil pressure higher? Just very curious about this.

Yes, it has the modded oil pump relief from Mazmart, I believe.

I think you ran it way too long and way too far. The oil is no longer a 40 grade. It’s oxidized and thickened up to a 50 grade.




I never understood why people choose to save $30 worth of oil but risk a $3,500 engine. Lol.




Blackstone’s comment on “oh you have low oil consumption for this type of engine... but that isn’t a bad thing” just goes to show how stupid the lab technician are. Low oil consumption on an engine that’s designed to consume oil IS A BAD THING. That means ain’t shit being injected to Lube the apex seals. :nono:



nice experiment though. I feel bad for that poor engine.

There’s a difference between new oil that starts @ 20w50 and a 0w40 that oxidized and broke down, then started thickening up and became a thick, out of spec 20w50. Lol.

I vote you ran that oil too long and Blackstone agrees, since they recommended you check back in 3k miles. HAHAHAHA.

You have copper and lead indicators in the oil. Those things are supposed to stay in the engine.

Especially on a 37000 mile lightly driven engine, that's kind of sad and completely avoidable. Look at the other UOA's here.

I suspect that time has some factor in this. Oil changes should be performed annually even if you don't drive the car that often. Owner's Manual actually recommends every 6 or 4 months depends on where you live. It becomes more and more acidic as you drive it, and leaving it in the engine can lead to a light corrosion.

AT may keep the RPM lower, but it also cooks the rear rotor due to the heat a torque converter will constantly generate, versus a clutch that will stay pretty cool unless you absolutely blow at driving a stick or your clutch is dying.

With short oil change intervals, I don't think I am missing out much with conventional oil, and given that I can only drain out 60% of the entire system and the way I drive my car, it's justified as well.

I am an engineering student, so reading comprehension does fail me sometimes. Point taken.

Anyway, that's what a UOA is for: you see the numbers and you adjust accordingly. I doubt one run like this will be too bad for your engine, and you will be adjusting the interval anyway.

I agree with Blackstone comment baloney; always good for a laugh seeing how deep they’re willing to stick their nose in a customers tail pipe, but otherwise spare us the regurgitated BITOG hokum

https://cimg9.ibsrv.net/gimg/www.rx8...a6b39dbdd.jpeg

https://cimg8.ibsrv.net/gimg/www.rx8...6aa3318485.jpg
Used Royal Purple 5w-20. Did an AutoX event within that interval, and this is my DD, roughly 45 miles each way to work.

^ You are a brave person, I'll give you that!

I use 5W-20 as well. Pretty sure my car has only seen 5W-20.

Last UOA I posted actually has 2 AutoX events on it.

Your iron wear is a bit high, more than twice of mine. But you had it in there for 10k miles? Wow, you have some guts.

IDK, Royal Purple to me is always a bit of a gimmicky brand. I stick with bigger, more reputable brands like Castrol and Pennzoil. I usually use Pennzoil because I can get a 5 L/5.5 quart jug for under CAN$20 when it's on sale at the local Canadian Tires.