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Recommend oil for rotary engine

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Old Dec 24, 2025 | 04:47 PM
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Recommend oil for rotary engine

What oil can I use on my FD?….Stock, I’ve always used Castrol 20-50 non synthetic here in Florida….Is it possible to use a Synthetic oil with the stock oil injection system?
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Old Dec 24, 2025 | 06:02 PM
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"No"

It depends who you ask but "no". Stick with the conventional or delete the omp and run full synthetic
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Old Dec 24, 2025 | 09:51 PM
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OR Get yourself the Rotary Aviation OMP adapter & plumb a simple gravity feed tank to it. Put the pre-mix lube of your choice in the oil tank and run synthetic oil in the sump. Best of both worlds.
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Old Dec 25, 2025 | 09:53 AM
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Some synthetics burn ashless, though which ones are debated. It's pretty much accepted that Idemitsu's rotary specific is a synthetic that burns ashless - I've also had a client accidentally run many cases (over a few years) of VR1 synthetic when he thought he was buying the mineral version of VR1, on teardown it looked great but a sample size of 1 isn't enough for me to make a suggestion on.
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Old Dec 25, 2025 | 01:34 PM
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Originally Posted by dguy
Some synthetics burn ashless, though which ones are debated. It's pretty much accepted that Idemitsu's rotary specific is a synthetic that burns ashless - I've also had a client accidentally run many cases (over a few years) of VR1 synthetic when he thought he was buying the mineral version of VR1, on teardown it looked great but a sample size of 1 isn't enough for me to make a suggestion on.
Thanks for the advice, and feedback everyone. I read a bunch of stuff on the Forum previously posted. I think I’ll stick with Castrol 20-50 mineral. I don’t drive the FD enough to make any changes…..1993 with 79k….original motor….and I don’t drive it hard!
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Old Dec 25, 2025 | 01:47 PM
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be sure you are doing a full throttle pull at least once when ever you do take it out
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Old Dec 25, 2025 | 04:37 PM
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Yea, you gotta rip 'er here and there if you want it to last bud!
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Old Dec 25, 2025 | 06:34 PM
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Originally Posted by FDAUTO
be sure you are doing a full throttle pull at least once when ever you do take it out
Originally Posted by fireindc
Yea, you gotta rip 'er here and there if you want it to last bud!
If you don't do that, deposits can build up in the combustion chambers and on the rotors and may cause issues down the road...
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Old Dec 26, 2025 | 07:13 PM
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Originally Posted by DaveW
If you don't do that, deposits can build up in the combustion chambers and on the rotors and may cause issues down the road...
yes….It’s impossible to drive the FD without whomping it a few times ….It begs you to do it!!😎
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Old Dec 27, 2025 | 11:11 AM
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Thumbs up

Originally Posted by DaveW
If you don't do that, deposits can build up in the combustion chambers and on the rotors and may cause issues down the road...
Exactly!

Originally Posted by Greg Sabol
yes….It’s impossible to drive the FD without whomping it a few times ….It begs you to do it!!😎

Yep .... Just remember "A daily revvin keeps the motor from going to rotary heaven".

Steve
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Old Dec 28, 2025 | 03:02 PM
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For non-synthetic, Valvoline VR1 20w50 is what I'd recommend year round in FL. It has added ZDDP additive, which is important for a rotary engine because of the harsh environment, to include the rotor ring gear to stationary gear interface.

"A ZDDP additive (Zinc Dialkyldithiophosphate) is a crucial engine oil supplement, especially for classic cars and high-performance engines, that provides superior anti-wear and anti-corrosion protection, forming a sacrificial layer on metal parts like flat tappet cams to prevent premature failure, though its phosphorus content requires lower levels in modern oils due to emissions systems, necessitating these additives for older vehicles."
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Old Dec 28, 2025 | 04:07 PM
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Don't use racing oils like VR1 that have additives like ZDDP, etc., if you are running a catalytic converter - they will ruin it in short order.

Last edited by DaveW; Dec 28, 2025 at 06:04 PM.
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Old Dec 29, 2025 | 10:20 AM
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Thanks again for the advice. The FD has the Racing Beat down pipe and exhaust 👍
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Old Dec 29, 2025 | 12:27 PM
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Originally Posted by Greg Sabol
Thanks again for the advice. The FD has the Racing Beat down pipe and exhaust 👍
No main cat? If so VR1 with ZDDP is OK.

However, an exhaust system with a DP and catback could still have the main cat unless it's been replaced with a mid-pipe or similar.
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Old Dec 30, 2025 | 10:45 AM
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Originally Posted by DaveW
No main cat? If so VR1 with ZDDP is OK.

However, an exhaust system with a DP and catback could still have the main cat unless it's been replaced with a mid-pipe or similar.
The FD has a mid-pipe...Thx.
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