Impact of synthetic oil on 1988 Mazda RX7 with 80k miles

[woodsman75]

We have a 1988 Mazda RX7 with an odometer showing 81k+ miles. We don't know whether it rolled over, but it has at least this many miles. Based on the condition of the car, I'm inclined to think it has 81k miles and not 181k miles. We bought the car from a dealership that had no service records. A rotary mechanic inspected it before purchase and said it was in great mechanical shape, and we drove it from FL to NC, and aside from a new battery, it was flawless.

We put in Idemitsu 20W-50 Racing Rotary Engine oil. Then we learned that some people at least, say not to use synthetic oil. At 80k miles and 35 years, the engine has been broken in. We can use conventional oil on the next change, but is the synthetic so bad that we should change it before driving it again? We
put on about 30 miles on the new synthetic.

As an aside, at $100 for 5 quarts, I don't mind using conventional.

 

[Revving2Redline]

I was under the impression that full synthetic might not burn off enough and these rotary wenkels need to consume oil. if so, I could say probably 10w,40 from Amsoil

https://www.amsoil.com/lookup/auto-and-light-truck/1988/mazda/rx-7/1-3l-2-cyl-engine-code-1308cc-2-turbo/

 

[MRC01]

I owned a '95 RX-7 and the manual said not to use synthetic oil. It didn't say why, but the engine had oil injection under high power and we RX-7 owners speculated that Mazda thought conventional/mineral oil burned cleaner. Mine was a twin turbo and I raced it in SCCA, always conventional mineral oil, never gave me any trouble.

 

[blufeb95]

Is that a racing-racing oil or a street "racing" oil?
I've always wondered is straight 30 or straight 40 CF-2 rated diesel oil would a good choice in a rotary, since it's meant to reduce build up in two-stroke Detroit diesels.

 

[wpod]

What advantage are you expecting from running syn oil?

 

[RooflessVW]

 

[ekrampitzjr]

Mazda rotaries meter or inject small amounts of engine oil into the fuel or directly (depending on model and year) to lubricate the rotor seals. Of course, that oil is burned during combustion. The story was ash buildup from burning synthetic oil could build up and cause problems such as detonation.

Even some of the rotary modifiers warned to stick with conventional oil instead of the full synthetics you would find in auto-parts stores. They would use a premix arrangement for racing.

The Idemitsu synthetic rotary racing oil is PAO and allegedly does not cause that problem. This was the oil the Mazda 4–rotor racer that won Le Mans in 1991 used. But it costs $$$$$.

 

[Jetronic]

Mazda rotaries meter or inject small amounts of engine oil into the fuel or directly (depending on model and year) to lubricate the rotor seals. Of course, that oil is burned during combustion. The story was ash buildup from burning synthetic oil could build up and cause problems such as detonation.

Even some of the rotary modifiers warned to stick with conventional oil instead of the full synthetics you would find in auto-parts stores. They would use a premix arrangement for racing.

The Idemitsu synthetic rotary racing oil is PAO and allegedly does not cause that problem. This was the oil the Mazda 4–rotor racer that won Le Mans in 1991 used. But it costs $$$$$.

Except the ash doesn't come from the base oil, but the metallics in the additive package.

 

[blufeb95]

Except the ash doesn't come from the base oil, but the metallics in the additive package.

But when PAO is exposed to extreme heat and oxidizes it tends to form a very hard varnish.

 

[Jetronic]

But when PAO is exposed to extreme heat and oxidizes it tends to form a very hard varnish.

yet, in the post I replied to:

The Idemitsu synthetic rotary racing oil is PAO and allegedly does not cause that problem. This was the oil the Mazda 4–rotor racer that won Le Mans in 1991 used. But it costs $$$$$.

So is PAO and varnish even an issue in an oil burner? At the very least the ash thing seems to be of more concern

 

[97prizm]

We have a 1988 Mazda RX7 with an odometer showing 81k+ miles. We don't know whether it rolled over, but it has at least this many miles. Based on the condition of the car, I'm inclined to think it has 81k miles and not 181k miles. We bought the car from a dealership that had no service records. A rotary mechanic inspected it before purchase and said it was in great mechanical shape, and we drove it from FL to NC, and aside from a new battery, it was flawless.

We put in Idemitsu 20W-50 Racing Rotary Engine oil. Then we learned that some people at least, say not to use synthetic oil. At 80k miles and 35 years, the engine has been broken in. We can use conventional oil on the next change, but is the synthetic so bad that we should change it before driving it again? We
put on about 30 miles on the new synthetic.

As an aside, at $100 for 5 quarts, I don't mind using conventional.

I have a 1984 Mazda rx-7 that I have raced. I've used Royal Purple 10w-40 with good results. I've met enough people with rx-7s that said the whole "no synthetic oil " issue came from issues with early synthetic oils.

 

[Greasymechtech]

You can use ANY oil you want. Keep it clean with toptier fuel, and don't baby it after its warmed up. And, no short trips! Get it fully warmed prior to every shut down. They normally run overly pig rich for emissions.
To vent the combustion chambers, prior to shutting down, rev engine to 5000rpm and then kill the ignition. Make it a habit.

I've run synthetic in my rotaries for over 35 years. Never had an issue. NEGLIGENCE is what causes rotary problems.

My only recommendation is 'clean oil'. Since the oil is injected, you should change the oil every 3000 miles, NO MATTER WHAT TYPE OF OIL OR BRAND, or filter.

Remove and clean the oil injectors and make sure they are working. If turbo, you're stuck with premium fuel. If non-turbo, then you can use whatever fuel you want but I've always used premium.

Tune up time... plugs, coolant, belts, thermostat, oil/filter, transmission fluid, diff fluid, brake bleed, hoses,....

Since it is oil injected, keep the oil full, checked often, and topped off always. The oil is also a major cooling source for the engine. Just look at that monstrosity of an oil cooler up front.

 

[Audiman]

Don’t forget a oil that is designed and used for racing has different requirements than one that has a a requirement to last thousands of miles and leave the engine in a condition it can last hundreds of thousands of miles.

The le mans 4 rotor would have been built for the race and built again for the next race.

 

[skyactiv]

I know someone that once had an RX8. Stated he always poured 2-stroke oil in the gas tank when fueling. So I would think if one is going to add 2-stroke oil when fueling up, it'd be best to use an outboard oil as those are ashless.

 

[Audiman]

I know someone that once had an RX8. Stated he always poured 2-stroke oil in the gas tank when fueling. So I would think if one is going to add 2-stroke oil when fueling up, it'd be best to use an outboard oil as those are ashless.

That’s what people who put 2-stroke oil in diesel use.

 

[97prizm]

I know someone that once had an RX8. Stated he always poured 2-stroke oil in the gas tank when fueling. So I would think if one is going to add 2-stroke oil when fueling up, it'd be best to use an outboard oil as those are ashless.

The mop or metering oil pump can fail especially without warning in high mileage vehicles. I know many a rotary owner that mix 2 stroke oil in the gas as a precaution

 

[Bladecutter]

Ex 2011 RX-8 owner here.

Best bet for long life of a valuable rotary engine:

Separate the two oil systems:

Have 1 oil system for the rotating parts of the engine, and run a high quality synthetic there.

The second system would then be the oiling system that injects oil into the combustion chamber in order to oil the apex seals in order to reduce wear. Buy a kit that would have its own oil reservoir for this purpose, and you reroute the MOP to pull the oil from the reservoir in order to feed the oil injectors with always fresh lube.

And if you want to add another layer of protection, 2 stroke oil into the gas tank on every fill.
That way, the apex seals are protected as well as can be, for as long as possible.

 

[DGXR]

Idemitsu 20W-50 Racing Rotary Engine oil sounds like it is specifically developed for use in rotary engines...?
If so, curious how it might cause problems. But I'm not a rotary guy either. Help me learn before lighting the torch.

 

[Greasymechtech]

Specially developed? Don't kid yourself. Specially marketed!!!!!! Understand the difference.

I didn't see the need to run 20w50 in my naturally aspirated 13b's, or the various brands of rotary oil marketed over the years.