I'm not sure if this has been asked before and im not sure how to look for it, so im just gonna ask. I know that with the rotary the MOP pumps small amounts of oil to keep it lubricated, and that you shouldnt run the full synthetic oil because the detergents in them are harmful to the apex seals, or so i have read many times, well i have MOP block off plates so i am premixing, i use a premix designed for the rotary engine. Anyway, common sense would tell me that i could use synthetic oil now since it is not being pumped into the engine rotor housings any longer, am I right?

 

The gentleman I use for rebuilds who has been building them for decades now... basically told me this.... don't use full synthetic breaking in the engine. After 3000 miles or so, run whatever I want (synthetic wise). Most if not all oils off the shelf are partially (<50%) synthetic anyhow.

 

If you've blocked off the OMP as you said, you can run any oil you like, full synthetic or Dino oil. If you're planning on changing the oil frequently, like every 3500-5000 miles you should probably just go with a good Dino oil like Castrol. If you want to take advantage of the extended change intervals of a synthetic, up to 15000 miles then use a good fully synthetic. I wouldn't recommend the synthetic blends. Whatever you use, I would recommend 10-30 or 20-50. You're in South Carolina so the summer heat can get tough. Use the 20-50.

 

This topic has been beaten to death, like a dead horses daddys uncles brother.

But, to answer you question...

In an RX7, conventional oil will be pretty much crapped out at 3,000 miles. If you do run conventional oil, never ever ever go past 3,000 miles on your oil. I am not regurgitating bullshit from jiffy lube, this is clearly defined in the FSM.

Also, 10w-30 is clearly outlined in the FSM as acceptable in just about any condition. 20w-50 is great when it is 100*F outside and you are beating the **** out of the car, but remember, the car has a cooling system that is regulated by a thermostat. The car is going to be running close to proper operating temperature regardless of the ambient temperature assuming the cooling system is functioning correctly. Oil viscosity is best chosen for the coldest temperature that it is going to see within your oil change interval.

Go and pour some premix when it is 40*F outside and watch how slow it comes out of the bottle...yes, it's a lighter viscosity than 20w-50

 

Back in the 1980s, some brands of synthetic motor oil didn't work well in the combustion process, creating a residue that caused striations on the rotor housings and broke apex seals. Modern synthetic oil is fine, and it is actually recommended for racing applications by Racing Beat, Mazdatrix, and Mazdaspeed Motorsports Development.

It is fine to use synthetic engine oil regardless of whether you have the OMP or premix, but common sense would tell you to not to waste your money on synthetic oil unless you intend your car to experience severe racing conditions on a dedicated race track. Castrol GTX works very well for street driving and autocross, and it is less expensive than synthetic oil.

Per the FSM, engine oil is good for up to 7,500 miles. Modern motor oil is better than it was in the 1980's, but I don't recommend exceeding the guidance in the FSM.

It's actually best to choose oil viscosity by both the coldest and warmest temperature by using the FSM chart that you referenced. Keep in mind that the engine temperature is not the same as the oil temperature, and the oil cooler does not work as well when hot ambient air is moving through it.

10W-40 actually has the largest range, and that is what I use in St. Louis. I totally agree that 20W-50 is great for hot weather, and that is what I used in Florida.

 

Agree and agree...

I was quoting the "extreme conditions" service interval. Typically, I feel most street driven cars fall under that catagory.

As for the viscosity, I was trying to make it simple for the guy considering the wide temp range in a place like North Carolina. I have poured 20w-50 in the winter time here in Texas and at 30*F the stuff is like molasses.

I personally run 10w-30 in the winter and 20w-50 in the summer as we have the weather here to support that. If I was further north like the OP, I'd just run 10w-30 all year long.

Here is where I do not agree.

10w-40 does have a wide range, but since the viscosity modifiers in oil break down, you pretty much have a 10w-30 in your crank case half way through your oil change interval. 20w-50 will behave the same way, but at least you still have a higher viscosity oil even when the modifiers are breaking down.

Last but not least, I am not trying to start an oil debate thread and start beating the dead horses great grandmother, just stating what I have learned by doing countless hours of research into oil, viscosity and everything else oil related. If anything, everyone should be worried by the lack of ZDDP in modern oil.

To the OP, If you really want good information on oil, and everything you could ever want to know about oil, check out bobistheoilguy.com

 

That was the case up until about the mid 90s. Welcome to the modern world, you can now use 10W-40 without fear of premature breakdown.

However, personally, I would tend to use 20W-50 in the Texas heat.

... if your engine has a valvetrain, which ours don't.

^ Agree.

 

if you run the car on the track, synthetic.

if you run the car on the street, dino.

you'll be changing the oil at the same intervals regardless so synthetic on the street is just a waste of money. during teardowns of engines i could see no discernable difference in wear on the bearings of any engine using either type of oil for street driven applications.

also "rotary specific" premix always gets me, even the cheapest 2 stroke lubricants do the job compared to these $10/qt "specialty" premixes.

in my personal car i run dino oil in the crankcase and walmart 2 stroke oil in the tank, and that engine had over 2 lifespans put on it and still runs.