Lycoming approve UL91 - what now?

[Curlytips]

OK - so they finally issued Service Instruction 1070R and I can use UL91 in my O-360A4M as long as I use Aeroshell 15W-50, but...........

Will I notice any difference in power?

Can I mix it with 100LL?

Any drawbacks anyone can see?

[stickandrudderman]

There's a lot of info about this over on the Flyer forum.

[A and C]

I don't see any problems with mixing UL91 with 100 LL in your engine however as usual with these things the devil is in the detail.

People reading these threads should take great care to make sure that they read and understand the Lycoming SB as for instance some O-235 engines can run on UL91 and some can't. It is the last three (O-235-***) in the engine designation that will tell you if your engine can run UL91 so check your engine data plate.

[Rod1]

“Any drawbacks anyone can see?”

Provided your engine is on the list you should have no issues. Mixing is no problem. Lyk are still testing so some other engines will probably be added in time. 91UL is Avgas so no Mogas type restrictions. If you look at flyer the 91UL launch thread has a lot of info.

Rod1

[A and C]

You do not have to use w15/w50 oil if you put the Lycoming additive ( P/N LW-16702 ) in the oil.

I would think that using the w15/w50 would be a much more convinent way of doing things and it has advantages of better corrosion resistance that would be important if you don't do a lot of flying.

As with all these instructions from Lycoming the small print needs careful reading.

[BackPacker]

Suppose an engine is on the approved list. Can you then start using UL91 straight away, or do you need for approval from the airframe manufacturer as well?

One of the issues with Mogas was that if certain types of rubber were used somewhere in the fuel system (which is obviously outside the control of the engine manufacturer), they could swell and/or deteriorate and either cause leakage or blockage.

Do we have the same risk with UL91?

[2high2fastagain]

In the wider sense of drawbacks (as Rod 1 hints), for me it's a looming disaster. My aircraft has a high compression engine and a turbo, so I don't think there's a sniff of a chance of UL91 working for me any time soon. If UL91 takes off and avgas becomes too expensive or too rare, then I guess it's a new engine (maybe a diesel heaven forbid!) or a new hobby and a potentially unsaleable aircraft asset.

It's a shame the GA community isn't holding out for a straight avgas replacement. I guess that was too much to hope for.

[Rod1]

“Suppose an engine is on the approved list. Can you then start using UL91 straight away,”

YES

Avgas 91UL is Avgas 100LL before the lead is added. EASA have cleared everything provided the engine manufacturer is happy.

“If UL91 takes off and avgas becomes too expensive”.

91UL is just as much Avgas as 100LL. The potential single fuel solution Avgas 100UL may come in time but will have a high price tag.

Rod1

[Stephen Furner]

Has anyone heard what the situation is for the older Continental engines? I understand they have agreement with LAA for use of UL91 in permit aircraft but so far I've not heard anything about its use in aircraft on a C of A. I tried e-mailing Continental for clarification a while ago but did not get a reply.

[Rod1]

If the engine is cleared for Mogas then you can use Avgas 91UL.

Rod1