90 octane auto vs. 100LL

by Roland Berg in General Tech Discussion 14 years ago

The preferred fuel for the Rotax 912 is 90 octane fuel. Never have seen 90 octane auto fuel at airports. To use 90 octane auto fuel it would require obtaining fuel from a gas station. Not worth the effort to do this, therefore, 100LL seems to be the only alternative. Have seen ads for Decalin additives to be added to 100LL to reduce the lead, but hesitate to use it since don't know what affect this additive may cause to both the Rotax and to system componets such as fuel tank, lines, etc.. Is it safe to add Decalin additive to the fuel or will it cause more problems than it is worth? Don't believe Rotax makes any rcommendation on it use.

Re: 90 octane auto vs. 100LL

by Roger Lee » 14 years ago

Roger Lee

131 5.38k 5.44k

Hi Roland,

This is a common topic, but an easy one.

You need to use 91 Oct. or higher for the 912ULS. The 912UL can use 87 Oct. because of the lower compression. Absolutely don't use 87 Oct. in a 912ULS. You can however use 87 oct. mixed at a 50/50 ratio or higher with 100LL. There has to be more 100LL than 87 oct. You are right that this 91 Oct. usually comes from a gas station. There are several airports in the nation that carry 87 oct Mogas, but darn few that have 91 Oct Mogas. Most of us using 91 Oct. bring it out to the airport in 5 gal. cans and just get stuck with 100LL when we travel.
If you use 100Ll use the Decalin, it will not hurt your plane or engine like TCP did. TCP had some harsher chemicals. Absolutely use the Decalin to help keep lead build up at bay. It is not a cure all, but does help. Using 100LL will not only have higher fuel cost, but carries a fairly higher margin for engine maint. (i.e. oil change intervals, gearbox rebuild and much earlier interior parts leading) 100Ll will not get you any further down the road than 91 Oct., just cost you more to get there, both in the short and long term out of pocket expenses.

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

Thank you said by: Roland Berg

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