Rotax recommended oil change interval - 100LL

by John Peck in 912 / 914 Technical Questions 13 years ago

I almost hate to bring this up, but since I have about 25 hours on my oil (50 hrs TTSN) I have to decide whether it needs changing or not. I run 100% 100LL. My engine uses essentially no oil between changes and it looks as clean today as it did when it came out of the bottle.

I am confused by the Rotax manuals on this subject.

Page 16 of Section 05-20-00 of the current Rotax Line Maintenance Manual says the oil should be changed at 100 hours, or 50 hours if running on 100LL.

However, SI-912-016-R4 Section 3.3 first lists 50 hours, then farther down this changes to 25 hours.

So, what is Rotax really saying here? 50, or 25?

Secondly, has Rotax published an opinion on the use of additives, such as Decalin?

Re: Rotax recommended oil change interval - 100LL

by Roger Lee » 13 years ago

Roger Lee

129 5.31k 5.12k

Hi John,

There is a little confusion and a little leeway on oil changes, but skimping on oil changes is like living with diseased blood in your body. So if you have a brand new engine change the oil at 25 hrs. for the first time. Always check the magnetic plug at every oil change as per Rotax. Rotax states in the manuals and SB that if you use 100LL then you should be using 25 hr. oil changes. You need to do this to help keep the lead from accumulating in the engine. Lead is bad and if you can switch to 91 Octane or higher unleaded auto fuel you will be way ahead of the maint. and extra cost game. Rotax says up to 100 hr. oil changes with unleaded auto fuel, but many of us do it at 50 hrs. which has been discussed at length in Rotax schools. For me 50-75 hrs is a max with unleaded fuel. Many people don't even fly that many hours in a year so it needs to be changed at the annual. Read the reasons why under the oil blog. If you leave oil in with the 100LL you will pay dearly later in your engines life. The oil may still be good at 25-50 hrs., but the lead will be accumulating where you really don't want it.
Rotax allows for Decalin and TCP, but admit they really haven't tested it. TCP has some harsh chemicals and it is recommended that it not even be carried in the cabin. Decalin is much milder and won't hurt your plane and I know at least a 100 guys that use it including myself and have good results with it long term. It cost about $19 for a bottle from Aircraft Spruce and you use 1/2 oz. per 10 gals. TCP and Decalin are both lead scavengers. You should also be running a little higher cruise setting with 100LL to help keep the lead blown out the exhaust. (i.e. 5200-5400 cruise rpm)

So change your oil at 25 hrs. with 100LL and 50-75 for unleaded. It's not about the oil with 100LL, but lead accumulation. Absolutely use a lead scavenger like Decalin. When using 100LL you will need to have the gearbox inspected at 600 hrs. and the slipper clutch disassembled and cleaned from all the lead. Unleaded fuel use is 1000 hrs. If you leave the clutch in and it gets to 800+ hrs. with 100LL then there is a really good chance the slipper clutch has so much lead that it may not function.

Always use a semi synthetic oil with 100LL and not a full synthetic.

You should have done a required 25 hr. TTSN inspection to keep your warranty and oil should have been changed for the first time there too. Make sure you keep good records on your engine and plane. It will pay you benefits later.
I hope this helped answer your questions and not confused you more.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Rotax recommended oil change interval - 100LL

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