Cleanest burning oils

Pennzoil motor oil
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jromano

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Hello, the subject of this post might seem weird at first, but I recently bought an RX8 which has different oil needs than most cars. It injects and burns a small amount of oil by design. So the main priority is a low-ash oil that will burn cleanly with minimal carbon buildup.

I'm thinking that group IV synthetics should be avoided. A high-ester oil like Redline 0w30 seems like a good option, but I'm not sure if it would really burn any cleaner than regular conventional oil. The most recommended premix is Motul 710, so it seems logical to want an engine oil with similar properties if it's being injected.

Does anyone have recommendations? Thanks
 
Okay, so are you referring to engine oil or the oil to add to the fuel as premix, or both engine oil and fuel?

What oil does the RX8's OP manual specify?
 
Sorry if I wasn't 100% clear. I use a very small amount of premix as additional insurance, but I'm asking for advice on the actual engine oil.

The US manual recommends 5w-20 and the international manuals recommend 5w30. But I want to choose a clean oil since carbon buildup is a common problem on these cars.
 
Originally Posted By: jromano
Sorry if I wasn't 100% clear. I use a very small amount of premix as additional insurance, but I'm asking for advice on the actual engine oil.

The US manual recommends 5w-20 and the international manuals recommend 5w30. But I want to choose a clean oil since carbon buildup is a common problem on these cars.

I would imagine any name brand synthetic would work?

Just my newbie to motor oil guess
smirk.gif
 
Well, if you can run synthetics, Pennzoil Ultra is about the most clean burning and low volativity oil on the market today.
 
Mazda initially recommended conventional oil, but it's not completely cut and dry. They also make a full synthetic specifically for this engine, but it's only available in Japan as far as I can tell.

Tc7Vyt3.jpg
 
From mazdatrix.com:

The Rotary engine has an oil injection system that injects small amounts of oil into either the intake tract, carb, or rotor housing (depending on year/model). This is needed to lubricate the various internal seals and surfaces.

The injected oil MUST BURN, and must burn clean. The root answer to the question is that not ALL synthetic oils burn, and not ALL of them burn clean. (Idemitsu Rotary Engine Oil is the only known exception) The ones that do not burn accumulate until they foul the spark plugs.
The ones that do not burn clean can leave residues of various substances (like ash? plastic? non-organic sand?) that accumulate until the spark plugs foul, or a seal sticks -- could be apex seal, side seal, corner seal, or oil control ring. The normal consequence of a stuck seal is an engine tear down.

In the many years we have been involved in rotary engines, we have NEVER had a problem with GOOD petroleum based oils. They work fine! They are less expensive than synthetics. (We use Castrol 20-50 GTX). They burn clean, etc. etc.
 
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On all my former rotaries, I NEVER used Synthetic. Especially my 93 Twin Turbo which had stock oiling with the omp. I used 5w30 conventional Castrol and also premixed 2 cycle oil with the fuel for lubrication of the apex seals.


My 89 Turbo II FC had a street port and I used a thicker Idemitsu 15w40 (I believe that was the weight) as conventional as that motor revved to 10.5k rpms.


For your situation, I would run 5w30 conventional, maybe Peak/Nextgen/Castrol GTX, and monitor the oil level closely. I would not premix your fuel if I were you in an RX8. Even with an ashless 2 cycle oil , I wouldn't want to effect your cat. I only premixed the fuel on cars with no cat for the track. They have way less moving parts but they are just goofy, have fun.
 
Originally Posted By: MolaKule
Well, if you can run synthetics, Pennzoil Ultra is about the most clean burning and low volativity oil on the market today.

I would likely choose a 5W-20 oil with a very low TEOST deposit (ASTM D6335) test score. The following is a comparison of some popular synthetic oils:
http://www.amsoil.com/lit/G3115.pdf

Pennzoil Ultra is good but Castrol Edge is much better.
 
The logic 10 years ago with the FD's was that they didn't want to use synthetic because the synthetic didn't burn quite as welland that is what caused the deposits. The gurus at the time stressed conventional. Made sense to me.
 
Originally Posted By: jayg
The logic 10 years ago with the FD's was that they didn't want to use synthetic because the synthetic didn't burn quite as welland that is what caused the deposits. The gurus at the time stressed conventional. Made sense to me.

A lot has changed in 10+ years, besides chemically there isn't a lot of difference between a GP II dino and a GP III synthetic other than the synthetic is more highly refined and therefore cleaner.
 
i have a 2009 RX8 R3 edition. i use Mobil Super 5000 5w20 and i premix 3oz of yamalube 2r every fill up. about 13 gallons.

if your Rx8 is older than 2009 the engine has 2 OMP squirters per rotar whereas the 2009+ have 3 and higher oil pressure. If its older than 2009 i would definitely premix 4oz+ in the tank. 5w20 in the sump. some use synthetic, but i do not. the Rotary is a pig rich beast and the oil will get fuel diluted fairly quick. i change the oil every 3k miles because only 4.6 of the 7 qts drain with each change.

with fuel dilution and not getting all the oil out each change i prefer to change more often. I researched a lot when i got my 8 and i dont see the benefit to synthetic in a rotary engine because of the reasons i listed above, and mazda doesn't recommend it either.

The rotary engine is sweet, but it is terrible on gas!!
 
Only available in Japan?
That could explain the can being labeled mainly in English?
 
How can the properties of GII+ be perfectly suitable while a GIII is not? How many conventional 5w20/30s claim to be exclusively GII anyway? I know of only one in Australia, it's made by Penrite and they promote it for use in the RX8 because of it.

Penrite 5w30


How is it good to use an ester based 2 stroke pre mix when it's not good to use an ester based oil in the crankcase (or is that eccentriccase)?
 
Originally Posted By: supercity
How can the properties of GII+ be perfectly suitable while a GIII is not? How many conventional 5w20/30s claim to be exclusively GII anyway? I know of only one in Australia, it's made by Penrite and they promote it for use in the RX8 because of it.

Penrite 5w30


How is it good to use an ester based 2 stroke pre mix when it's not good to use an ester based oil in the crankcase (or is that eccentriccase)?


The premix i use is not ester based. i use a semi-syn like yamalube. I do see your point and it is why i chose to not use and ester based/fully synthetic premix.
 
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