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question for oil experts, Rotax experts

hevansrv7a

Well Known Member
The Rotax documentation says that an acceptable oil is any heavy duty motorcycle oil, synthetic preferred, which is designed to properly lubricate the gears.

I have 1 bottle of this oil (picture).Screen Shot 2022-08-25 at 2.46.15 PM.jpg

My question is whether is is OK to mix some of that kind of oil with the special Shell/Rotax oil that is already in my "12".

I'm not using leaded gas, just premium mogas with up to 10% ethanol. I just want to top it off, not use a lot of it. It would probably be half a pint or less added to the 3 quarts or litres minus what has been lost/used.

Along with yes or no, some reasons would be helpful.

I learned today that the Aero Shell Sport Plus 4 is currently hard to get. I bought 4 bottles today from a Rotax authorized shop who also told me they are being told to limit the sales to one case (12) per customer. Aircraft Spruce is backordered to the end of September.
 

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Do a search here. I don't think mixing or using some of a liter as make up oil between oil changes would hurt anything, but I do think a straight 20w-50 is a little "heavy" if a full oil change was done with it. The lighter viscosity when cold is needed so that with reduced engine rpms when cold, the oil line between the oil sump and the oil pump doesn't collapse and starve the engine of oil pressure.

Some, including a flight school of RV-12s in Boise Idaho, have run strictly unleaded mogas and Mobil 1 Racing 4T 10w-40 motorcycle oil in their Rotax engines. It has gearbox additives in the motor oil, good for the Rotax gearbox too. So, you can consider that an option also. Some here run it religiously.

I know I've run it, with 50 hour interval oil and filter changes on strictly Mogas, and it works fine and protects the gearbox internals also.

It can be hard to find, but it does work well, if all you run is Mogas, religiously, as full synthetic motor oils don't suspend lead well in the engine.
 
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Do a search here. I don't think mixing or using some of a liter as make up oil between oil changes would hurt anything, but I do think a straight 20w-50 is a little "heavy" if a full oil change was done with it. The lighter viscosity when cold is needed so that with reduced engine rpms when cold, the oil line between the oil sump and the oil pump doesn't collapse and starve the engine of oil pressure.

Some, including a flight school of RV-12s in Boise Idaho, have run strictly unleaded mogas and Mobil 1 Racing 4T 10w-40 motorcycle oil in their Rotax engines. It has gearbox additives in the motor oil, good for the Rotax gearbox too. So, you can consider that an option also. Some here run it religiously.

I know I've run it, with 50 hour interval oil and filter changes on strictly Mogas, and it works fine and protects the gearbox internals also.

It can be hard to find, but it does work well, if all you run is Mogas, religiously, as full synthetic motor oils don't suspend lead well in the engine.

Here is the relevant page from the Rotax manual. If I am reading it correctly, the oil I bought should be OK down to zero F. I don't fly in weather like that. But the real issue is the compatibility of the oils. Thanks for the additional information. Also, I always keep the engine warm in the hangar all winter long.
 

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The Rotax documentation says that an acceptable oil is any heavy duty motorcycle oil, synthetic preferred, which is designed to properly lubricate the gears

That is not an accurate statement. Where does it say that?
The Rotax Service Instruction is the proper reference:
So, strictly speaking and referring to the SI, the answer to your question would be NO. Nowhere does it approve a mix of different types and weights of lubricating oil.
 

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That is not an accurate statement. Where does it say that?
The Rotax Service Instruction is the proper reference:
So, strictly speaking and referring to the SI, the answer to your question would be NO. Nowhere does it approve a mix of different types and weights of lubricating oil.

Here is the page in the Operators Manual. I am not trying to argue with you, just show that my statements were justified. If there is a contradiction between the SI and the OM then it's a problem for all of us.

As for mixing the oils, the absence of an OK is not necessarily persuasive. It's a reasonable, safe assertion for you to make but it's not all that clear.
 

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Rotax now officially seems to recommend only ShellAero Sport Plus 4 for use in 912 ULS engines no matter what fuel is used. In the past Rotax listed oils that were “recommended from the authorized distributors”. Those recommendations were further divided by unleaded or MOGAS and unleaded fuels. The service instructions document I'm referring to is from 2011 (SI-912-016). The current Rotax Service Instruction document does not make the same “recommendations”. The 2011 document recommends, among other oils, Mobil 1 Racing 4T / MX4T and Mobil 1 V-Twin for use with unleaded or MOGAS fuels. Interestingly the 2011 document specifically lists MOTUL 5100 Synthetic Blend as “. . . not suitable for engines types 912/914 series” for use with avgas because of a formulation change.

Both the 2011 and 2021 Rotax Service Instruction documents in section “ 6)” refer to oil types. Paraphrasing: If temperatures exceed 250 degrees F no matter which type fuel used, don't use petroleum or mineral based oils. If temperatures often exceed 250 degrees F, and you are using an unleaded or MOGAS fuel, use of a high quality synthetic oil is recommended.
 
I learned today that the Aero Shell Sport Plus 4 is currently hard to get

I did notice some supply issues a couple months ago.

In previous versions of this document, up to SI-912 i001-R2 / SI-912-016R7 (dated 9/23/2013), they included more recommendations and information for oils to use (see below).

Once they introduced AeroShell Oil Sport Plus 4 "with new formulation in red bottle" (the super secret RON424 specification, the old formula was API SL specification), they changed their document to ONLY recommend this oil. The change occurred between Rev2-Rev3, which was between 9/23/2013 - 4/16/2015.
 

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The answers from Rob Carsey and from azonslow were VERY helpful but not in the way i expected.

I discovered my SI was out of date. I downloaded the latest one. They are correct that Rotax ONLY recommends the Aero Shell Sport Plus 4 and "in the red bottle". Wow.

Oh, btw, the Motul oil I have is not a blend and is not what was referred to under the identifier "5100". However, that's moot now since Rotax is recommending ONLY their own special, blend which meets their (literally) secret standard.

The SI that I have, now, is 30 December, 2021.

Case closed. It's no longer a question of mixing since no other oil is now OK.

Thanks to all who responded so quickly.
 
I would have come to a different conclusion..

The Motul TWIN 20W50 apparently is mfg to the API SL specification (according to a datasheet I just pulled up).. which is the same as the old Aeroshell Sport Plus 4 spec. I don't know why Rotax changed their recommendations -- whether they didn't want to be liable for recommending products that they had no control over, or what.. but the fact is that many 912 engines ran with API SL oil for years and they weren't blowing up left and right.

Additionally, this is a synthetic oil.. and you said you're running mogas (no lead).. which is also fine.

Lastly, the viscosity of Motul is 20W50 vs Aeroshell's 10W40 -- a little different.. but as you pointed out, different viscosities are OK, as long as you're operating in the right ambient temperature range for it. Realistically, if you have 2 liters Aeroshell and 1 of Motul mixed.. the viscosity is something like 17W47.

I often thought about what I would do if I were "on the road" somewhere and noticed my dipstick was low unexpectedly. The chances of the local FBO or A&P shop having Aeroshell Sport Plus 4 are nil. But then I remember that yes, you can use these other oils. API SL is a 2001 standard.. there are newer/better standards like API SM.. and perhaps Rotax just wanted to get with the times and encourage the use of more modern/better oils. Nobody pays much attention to the API stamp on the back of the bottles..so the safest thing was to standardize on one "red bottle".
 
monopoly

Shell effectively has a monopoly on Rotax 4 stroke oil because they are the only manufacturer that has the formula spec from Rotax, apparently. Sport Plus 4 is also more expensive than the other oils that were previously acceptable, apparently.
 
The SAE SL standard is just one standard for motor oil, for automobile engines.

The other standard, for Motorcycles, because of the oil being shared by the gearbox is JASO MA2. Gearbox oils end up usually having a lot of ZDDP wear additive package added. Fine in motors without catalytic converters, but that additive is not good in newer vehicles with pollution controls.

It's the gearbox additive that's needed by the Rotax engines.
 
The SAE SL standard is just one standard for motor oil, for automobile engines.

The other standard, for Motorcycles, because of the oil being shared by the gearbox is JASO MA2. Gearbox oils end up usually having a lot of ZDDP wear additive package added. Fine in motors without catalytic converters, but that additive is not good in newer vehicles with pollution controls.

It's the gearbox additive that's needed by the Rotax engines.
I'm not trying to make an argument for motorcycle oil, Motul or any other. But the Motul in this case does have the JASO MA2. See picture.
 

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