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100LL and ROTAX 912ULS


NC Bill

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Just watched the ASA video ROTAX 912 ENGINE INTRODUCTION with Phil Lockwood.

 

In it he advises that if you are going to use 100LL as primary fuel there are 4 things to do to increase engine life:

 

1- use dinosaur oil - no synthetics

2- use Declan

3- adhere to 25 hour oil/filter changes & clean bowl at least every 100 hours to remove lead deposits.

4- cruise at 5000RPM or higher

 

The first 3 sound pretty basic. Is running at or above 5000RPM generally agreed?

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Hi Bill,

 

Yes running at cruise at 5000rpm or better is advised, I think the CTLS manual has a warning that if you use 100ll you should avoid prolonged operation below 4800. 5000 is even better, and your prop should be pitched in such a way that you can reach about 5500 at full throttle level flight. The Rotax was designed to run at those RPMs all day long, if your not able to get to those RPMs during normal flight your engine is being loaded to much and can cause eventual damage. I know it is louder in the cockpit, and even seems strange if your coming from Cessna and Pipers but your Rotax will thank you for it!

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The RPM thing is true, from what I've read, regardless of 100LL. The engine and gearbox was designed to run continuously at a high RPM. Anything less is like lugging a car in high gear... 'won't kill it, but introduces stresses and vibrations that can contribute to a shortening of engine life. I think FD had a service bulletin that warned against lugging the engine on climb-out.

Tim

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The Rotax is better run at 5300 rpm with 100LL in conjunction with the Decalin lead scavenger additive. Low cruise rpms with 100LL just causes excessive lead build up. The higher rpms helps keep the lead blown out the exhaust and not settle places you don't want it. As far as the Dino oil you should not be using that and I hope that was Lockwood's older video. Rotax does not recommend the mineral oil over synthetics, but does recommend semi or full synthetic. You're right not to use a full synthetic as it does not suspend the lead in 100LL, but you should be using a semi synthetic which does suspend the lead and is far better than a straight mineral based oil. There are some good full and semi synthetic oils out there that most anyone can get.

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