Grandfather's suggestion, input?
 

I recently bought my grandfather's 1988 RX7 10th anniversary edition first run with the black Mazda decals, has 36,000 miles(woo!!) And is currently on its way to me. Bone stock. I researched a lot and found 20w50 Royal Purple was the oil of choice for the engine, however he suggested using 20w50 Phillips aviation oil. In comparison it seems like it wouldn't be a bad oil to run through this engine especially with the low Ash, however I definitely wanted to check with people who are more experienced than I am, because he does have dementia and aviation oil in the engine seems to be quite the debate... however I'm inclined to believe that he knows what he's talking about because he was an airplane mechanic/instructor for 55 years, and taught me everything I know about Mechanics for cars and for airplanes.

any input?

Literally almost anything but royal purple.

Is Royal Purple that bad?

Can you elaborate more on this "first run" of 10ae with black decals? I've never seen/heard of this, and I own a 10ae. They were only produced for a single model year, so I find it strange that there would be any production differences.

From what I've been told, some had Mazda written in black on the front, and others did not.

from a site I got this quote "The 10th Anniversary Editions are based on the RX-7 Turbo II, so this car features a 1.3-liter turbocharged rotary engine making 187-horsepower and a five-speed manual transmission. The black Mazda logo on the front and the bright gold rotary badge on the fenders indicates that this example is part of the first series of 10th AE RX-7s, as the second series lacked the logo and had yellow-gold badges"

every rx7 has the front badge, it was either silver or black depending on the exterior color.

the side badge for the 10AE actually looks like it might have changed, although good luck figuring out which one is which. there is a different part number for cars made after 4/01/1988.

If it were me I'd just run GTX 20w50 and be strict about oil changes every 3000 miles.