In case you're wanting an astoundingly clean FC RX-7 Turbo

This car is insane, only 46k miles. Nm, not affiliated.

https://sfbay.craigslist.org/pen/cto/5908240147.html

I thought you couldn't use synthetic oil in a rotary?

I lost track on how many of those I parted out years ago.

rustybugkiller wrote: I thought you couldn't use synthetic oil in a rotary?

You can't use a certain brand in a rotary (Amsoil, I thought) but so it wouldn't look like they were singling a single manufacturer out, they said "No synthetics at all."

Of course, if you eliminate the MOP and premix yourself, or get one of those fancy plates that feeds the MOP from a separate tank of oil, you can run whatever you want in the engine, even shoddy early 80s synthetics!

More realistically, there is no point to running synthetic oil. If you use the MOP then the oil needs to be replenished frequently, if you don't use the MOP then the oil gets diluted with gasoline and needs to be changed frequently (this happens regardless, it's just noticeable with the MOP disabled - RX-8s seem to burn a lot more oil than RX-7s because blowby gases don't make it past the oil control rings, it goes out the side exhaust ports instead, so they don't add gasoline to the oil) and in any case, if the oil gets hot enough that conventional oil isn't good enough, it's probably not going to start again after it cools back down. Oil temps over 200-210F are pretty much "oh berk, shut it off!" time, conventional oils handle that no issue.

So there isn't any practical reason to use synthetic, you don't need the heat resistance benefits and you can't use the long oil change interval benefits.

Why not amsoil?

My guess, whatever synthetic oil that was the problem was burning with a very high ash content, which is Bad in an engine designed to burn oil.

I guess "Amsoil" because for the longest time, they were not API rated.

You don't want to use any oil that leaves a heavy ash residue when burned.

At one time Mobil 1 burned very clean & I used it, then the Amsoil turned out to burn cleaner and I used it.

I kept testing because it seemed formulations changed so the oil I used changed occassionally.

Aside from the residue and failure to completely burn that the synthetics exhibit (as discussed above), think about it from a cost perspective - you're just going to burn it up anyways - might as well use dino oil.

I honestly never changed the oil in my rotaries (single turbo RX7, single turbo RX8, C-Street RX8) - I'd change the oil filter every 5,000 miles or so and add oil as necessary - usually a quart after a good day of racing.

I have to change mine every 1000-1500 miles or so. Can't run a PCV system and the oil never gets hot enough to evaporate off the blowby. I do an oil change with only 4 quarts in the pan (at the "add" mark) and after 1000-1500 it's a quart over the full mark. (I really want to send Blackstone a sample just to see what their reaction is) I change the filter every 10k or so.

This is something inherent to rotaries. There's something like 12 linear inches of side seal on each rotor face, blowby happens. When they were running in GTU, they developed a way to quickly change the oil during a pit stop.