Help me please, I am confused about which oil to use, mineral, semi-synthetic or full synthetic and how many quarts of oil are used for mazda rx7 FD

 

we kind of just went over it, https://www.rx7club.com/3rd-gen-gene...t-ons-1161131/

 

You will always be confused about it ..... you will question yourself from time to time about your decision. There is so much discussion on this. This and to premix or not to premix, sump omp or 2 cycle.....

 

You’ll only really replace about 4 quarts of oil during a change. The rest will be stranded in the rotors, lines and depending on your model, oil cooler(s).
Use a shorter interval, use your eyes and nose when checking levels.

 

I was asking the same oil question. Most posters are just saying what they use, rather than more technical reasons.
I remember reading somewhere in the Rx7 archives that Mazda at one time said not to use synthetic oil in the Wankel, with the rationale that the engine was designed to burn some oil when running, to keep the rotor seals lubricated. Synthetic oil, they said, has a higher burn temperature, so instead of the synthetic burning, it tends to gum up on the seals. Then someone posted that that was arguably valid for the earlier formulae for synthetics, but the later synthetic formulations do not cause the gumming problem.
I was hoping for a latest technical opinion from an engine oil engineer that supports either theory.
Some searching here on the site did not take me to the desired information, if it is here.
Meanwhile, I have been avoiding synthetics.
Cheers.

 

From the 1994 Factory Service Manual:

 

I think its a discussion to have with your engine builder.
https://www.racingbeat.com/mazda/per...etic-oils.html
https://mazdatrix.com/using-syntheti...otary-engines/

IMO(which probably doesnt mean much) is if its a stock motor, especially using the OMP, I would use standard oil as it will burn better than most synthetics. I have seen people isolate their OMP and create a secondary tank specifically for 2-cycle oil. This and removing the OMP and strictly premixing might be a situation where you could potentially use synthetic oil as you are not introducing it directly into the motor.

 

For regular street use any quality mineral oil. I don't, however, follow Mazda's 30wt recommendation on FDs, I've always stuck to and recommend 50wt. That said, I'm in California - those in very cold climates may disagree.

 

Think about those turbos also!!!

 

The FSM and owners manual is probably the closest you’ll get to an “oil engineer ‘s” opinion. Of course being based on oil formulations of 40 years ago, a bone-stock car being daily driven in all climates with emissions and warranty concerns,…it might be a bit dated. But in the absence of an Oil engineer who’s also intimately familiar with a 13b REW…there you go.

My only recommendation is to go back thru all the previous threads and examine the posts and posters for their experience and rationale for the choice they made. THAT should probably be the “desired information” to look for. Then make your own decision.

 

Or you can do some experiments. Burn some different oils and see what kind of residue is left. Or, you can look at the inside of some motors and compare the build up on the rotors. These are a couple of things I did.
it is easy for some race guys to say synthetic as they rebuild quickly and synthetic of today are definitely not the same as 1993.
It is easy for Dino guys to say non synthetic as that's what the out of date manual states.

Same goes for viscosity. Are you going to really run this thing hard? 50 weight is pretty damn heavy for a dd. Utilizing 2 stroke in a separate sump for omp. Does the 2 stroke oil have enough viscosity spread and actually lube the seal? I believe it is suppose to "drip" and not spray. Tough call. Maybe sump oil regularly changed is the best route. Obviously an engine builder that isn't trying to push a product would be an invaluable source.
Don't forget using meth can wash away lube, so any lube premix or not, you may want to make sure it is compatible with meth (if you're using meth inj)

There is definitely a lot of bs out there and people pushing false info. Ultimately speaking lube is lube and from what I have read there are many people using all types that seem to do just fine.

I know the last I looked in my engine with a scope while changing turbo gaskets the rotor housings looked beautiful with 10+k miles and aftermarket apex seals. The rotors has minimal build up and this was with Royal purple HPS and the smallest nozzle injecting water. I have a pretty conservative timing. I ended up choosing RP vs Idemitsu for cost and much easier to source. I just change the oil with some serious ocd happening. I figured if I am using sump oil, ai will try and make sure it is clean (as can be). BTW, you can mix RP HPS viscosities with ZERO issues according to RP themselves.

Why did I go synthetic? I found it burned as clean as Dino in my own experiments. It is superior in lube and breakdown according to multiple tests. Temp runs cooler and many people have used synthetics on here. Why did I choose RP or Idemitsu? I spent a lot of time speaking with both companies. RP was easy to get a hold of. IDEMITSU was a pain in the *** during covid times. I would prefer Idemitsu, but costly and mostly just availablility. I use Idemitsu premix.
All this said I see absolutely ZERO reason why any good old Dino oil can't be used. Just change it often as any oil will get diluted with fuel after awhile and I wouldn't want to be dripping dirty oil into my combustion chamber and lubing my apex seals with gritty oil.

 

This is the main mindset I've taken as well. It also seems like the Mazdatrix article is saying something similar (I think the Racing Beat article is just too out of date to put much stock in). As they allude to in the article, there are just too many variables in engine builds, engine uses, and fuel used to make a blanket statement. This is why @iceman4357 's answer is probably the "best": talk to your builder. This even goes for those that have stock engines....Mazda is your builder....go with their recommendations.

I think on thing that needs to be considered more now, than maybe when Mazda did their testing, is the ethanol content of modern fuel. You don't need to have your car set up for E85 or flex fuel to see some ethanol contamination in your oil. Since fuel dilution is all but unavoidable, I think its best to have an oil that can hold up to fuel dilution. I think this is an aspect of this question that gets glossed over far too often. If we could get actual analysis based of this, it think we'd be able to move towards that "umbrella-type" answer to the question. I'd really like someone to do an independent test of the renewable lubricant's engine oil. Their claims are really promising, in my opinion. Penrite oil also claims to hold up well to ethanol, but finding that in the states is proving to be difficult.

As an aside [AKA Rant]: I think this is the reason that this question is so hated by the long-time rotary crowd. It's not so much that the question has been asked to a ridiculous degree over the years (and YES, it has been asked far too often), it's because there is no way of really giving a good answer. Especially since newer owners just simply ask: What oil should I use? No mention of modifications, turbo or N/A, usage, fuel, or hell...half the time they don't even say which engine/car they got. Then it just devolves into people saying what they use. They they start arguing amongst themselves about the answer, but meanwhile, the people arguing don't even have the same setup, or the same setup as the OP. So while each answer may be valid for each person, it's not appropriate for the other person, or even the OP...so the argument is pointless. [/Rant]

 

It is definitely frustrating as many builders opinions vary also. I remember taking hours upon hours researching this. It was painful and still is.
Ultimately, I would say oil is oil when it really comes down to it. My 1st rotary (2nd gen NA) gave me 198k miles a pure redline enjoyment until the heater core blew and I had no idea how bad over heating could be... all this on Quaker state 10w40... who would have ever though it possible lol....
I do get the turbo rotary is a whole different animal, bit how much debate was and goes on about 10w40 lol

 

I am in the dino camp, since my understanding is that the main advantage of synthetic is you can go longer between oil changes with it, but longer is not the best idea in a rotary. especially if it is raced, autoxed, or driven very hard very frequently. as multiple people said, the oil will get contaminated given the nature of the rotary.

But i will also add that synthetic has progressed from when i used to think it wasn't the best given the rotary burns it. Now my personal non-oil-engineer opinion is it might be ok. But if you are changing more frequently that the 10k or 15k or whatever synthetic manufacturers are claiming now, then the additional price doesn't justify it.

 

Unless you consider how much better synthetic performs in really high temp and high shear-force environments…..which the REW definitely has. But I agree, anyone that goes 10k between changes on a rotary should have their face on a can of beer and their keys taken.

 

hi, thank you for your messages it helps me too.