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Calculator for % MOGas Between Oil Changes


andyb

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My understanding is that the Rotax guideline is that if more that 30% of the gas used is Avgas (and therefore less than 70% is MOGas), then the oil change interval is 25 hours, rather than 50 hours.

 

I just had my first 25 hour oil change, looked at the cost, and came to the conclusion that there's a pretty good economic incentive to be below the 30%, to say nothing of it's being better for the engine.  I've therefore attempted to keep track of how much fuel that passes through the engine during a given interval (between oil changes) is which kind of gas.  I believe that it's a bit more entailed than what's actually been put into the tanks between oil changes, as that doesn't account for what was the makeup was at the time of the change, and also because just because a given kind of gas has been put into the tanks, it doesn't mean it was burned by the engine.

 

Therefore, I've attempted to put together a spreadsheet that calculates this, which is attached.  Green cells are for input.  Not sure I've gotten out all the calculation glitches, but feel free to use it, and certainly to advise if I've made any mistakes in the cells or the logic.

 

Given that this is amateurish, and not fully scrutinized, strongly suggest using your own independent calculations for any decision making.

 

Andy

 

P.S.  Okay, the Excel file didn't seem to download.  Any how-to advice?

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You should not try to tweek mixing or tracking your fuel if you want to go to the 50 hour oil change interval.  You can burn all Mogas by investing in a fuel trailer, or a fuel transfer tank for a pick-up truck.  Some also hand fill with jerry cans but that has to be a pain in the rear.

 

When getting fuel away from home you can use 100LL but you need to zap the lead with TCP.  Decalin Runup is good for that purpose...you can take some with you on trips.  http://decalinchemicals.com/products/decalin-runup-fuel-additive/

 

Use 91E10 premium grade gas.  And switch to all synthetic Mobil 1 4T motorcycle racing oil which can be bought at Walmart.  Make sure you always use Rotax oil filters...they are designed specifically for the engine.

 

Here is a picture of a fuel trailer I built for the purpose:

post-940-0-00647200-1446669308_thumb.jpg

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You should not try to tweek mixing or tracking your fuel if you want to go to the 50 hour oil change interval.  You can burn all Mogas by investing in a fuel trailer, or a fuel transfer tank for a pick-up truck.  Some also hand fill with jerry cans but that has to be a pain in the rear.

 

When getting fuel away from home you can use 100LL but you need to zap the lead with TCP.  Decalin Runup is good for that purpose...you can take some with you on trips.  http://decalinchemicals.com/products/decalin-runup-fuel-additive/

 

Use 91E10 premium grade gas.  And switch to all synthetic Mobil 1 4T motorcycle racing oil which can be bought at Walmart.  Make sure you always use Rotax oil filters...they are designed specifically for the engine.

 

Here is a picture of a fuel trailer I built for the purpose:

At my home airport, I exclusively fuel the plane with 91E10.  I presently use Tuff-Jugs (think that's they're called) and I don't find them too burdensome.  I'm considering the trailer you use, but the car I drive won't accept a trailer hitch, so there's a complication there.

 

The issue for me is fueling when I have to, when I'm away from my home airport.  Given the gross weight restrictions, on a flight of any length, in which I'm taking a passenger, I need to get fuel before coming home.  Is the TCP additive approved by Rotax, and if so, does it mitigate the need to be <30% avgas?  If not, I don't know how I can get away from calculating the %.

 

I use AeroShell Sport Oil, which is the one recommended by Rotax.

 

Andy

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Lets see, 50 hours times 5 gal / hour = 250 gallons times 30% = 75 gallons.  

 

How about 50 hours or 75 gallons of avgas which ever comes 1st?

 

Exception would be 75 gallons of avgas before 25 hours, then 25 hours is the limit.

 

 

I have an old cheap fuel trailer but it does have both a bonding cable and a ground.

 

post-6-0-95618300-1376752006_thumb.jpg
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At my home airport, I exclusively fuel the plane with 91E10.  I presently use Tuff-Jugs (think that's they're called) and I don't find them too burdensome.  I'm considering the trailer you use, but the car I drive won't accept a trailer hitch, so there's a complication there.

 

The issue for me is fueling when I have to, when I'm away from my home airport.  Given the gross weight restrictions, on a flight of any length, in which I'm taking a passenger, I need to get fuel before coming home.  Is the TCP additive approved by Rotax, and if so, does it mitigate the need to be <30% avgas?  If not, I don't know how I can get away from calculating the %.

 

I use AeroShell Sport Oil, which is the one recommended by Rotax.

 

Andy

 

Rotax min fuel is 91E10 and 91 without ethanol for the 912ULS and 912iS.    Rotax says its okay to use but does not recommend 100LL since the the lead content accelerates wear on the valve seats, create deposits in the combustion chamber and sediments in the lubrication system and gearbox.  And if you use 100LL you must change the oil each 25 hours largely due to lead buildup in the oil.

 

Decalin RunUp scavenges lead in 100LL after combustion to prevent lead oxide buildup on valves but still allows the lead to perform the anti-knock function prior to combustion.  And prevents valve seat erosion from valve seat micro welding. It is equivalent to TCP.

 

Decalin is not allowed in certified aircraft.  But is allowed in SLSA and experimentals.

 

Once you use Mogas exclusively (using Decalin on occasional use of 100LL still keeps you in the 50 hr change) you can then use Mobil 1 4t motorcycle racing oil full synthetic which is better than the Aeroshell for temperature and wear. 

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Once you use Mogas exclusively (using Decalin on occasional use of 100LL still keeps you in the 50 hr change) you can then use Mobil 1 4t motorcycle racing oil full synthetic which is better than the Aeroshell for temperature and wear.

Can you tell me where you got the information on Decalin use extending oil changes, and where it says that the mobile is better than Aeroshell?

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That's a very good point.

 

With just under 18 gals usable, for me even short out and backs usually require a topping off with 100LL - to no apparent ill effect.

 

I'm jealous of your bigger tanks - and lighter empty weight - in case it isn't obvious.

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Two points:

 

1)  Decalin is a "lead scavenger" and not a "lead eliminator".  It does lower the lead deposits in the engine and gearbox, but that lead then tends to deposit in the exhaust.  Some have said lead deposits in the exhaust can cause brittleness in the exhaust pipe that can then lead to cracks or other issues.  I use Decalin, but it's not a cure-all for lead issues.

 

2) The only oil currently recommend for the Rotax 912-series engines is the new (red bottle) Aeroshell Sport Plus 4 formulation.  You can use other oils and they may be acceptable in that use, but they are not recommended by Rotax.  

 

Just my two cents, I fully support people doing whatever they want with an engine they paid a lot of money for.

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Two points:

 

1)  Decalin is a "lead scavenger" and not a "lead eliminator".  It does lower the lead deposits in the engine and gearbox, but that lead then tends to deposit in the exhaust.  Some have said lead deposits in the exhaust can cause brittleness in the exhaust pipe that can then lead to cracks or other issues.  I use Decalin, but it's not a cure-all for lead issues.

 

2) The only oil currently recommend for the Rotax 912-series engines is the new (red bottle) Aeroshell Sport Plus 4 formulation.  You can use other oils and they may be acceptable in that use, but they are not recommended by Rotax.  

 

Just my two cents, I fully support people doing whatever they want with an engine they paid a lot of money for.

 

"Decalin RunUp scavenges lead in 100LL after combustion to prevent lead oxide buildup on valves but still allows the lead to perform the anti-knock function prior to combustion.  And prevents valve seat erosion from valve seat micro welding. It is equivalent to TCP." < right off the Decalin website.  http://decalinchemicals.com/runup-fuel-additive/

 

The recommended oil for the 912 when using leaded fuel is the Aeroshell Sport Plus (semi synthetic).    If you use Mogas exclusively (and if using 100LL use Decalin to deal with the lead) you can use a full synthetic oil - the oil recommended in that case is  Mobil 1 4T motorcycle racing oil (call California Power Systems or FD USA to verify this is true).  https://mobiloil.com/en/motor-oils/mobil-1/mobil-1-4t-motorcycle-oil

 

There is no question the use of leaded fuel is a problem for the plane...the oil change intervals are half when using Mogas, and the major  maintenance interval on the gearbox is twice as long as when using Mogas.

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"Decalin RunUp scavenges lead in 100LL after combustion to prevent lead oxide buildup on valves but still allows the lead to perform the anti-knock function prior to combustion.  And prevents valve seat erosion from valve seat micro welding. It is equivalent to TCP." < right off the Decalin website.  http://decalinchemicals.com/runup-fuel-additive/

 

The recommended oil for the 912 when using leaded fuel is the Aeroshell Sport Plus (semi synthetic).    If you use Mogas exclusively (and if using 100LL use Decalin to deal with the lead) you can use a full synthetic oil - the oil recommended in that case is  Mobil 1 4T motorcycle racing oil (call California Power Systems or FD USA to verify this is true).  https://mobiloil.com/en/motor-oils/mobil-1/mobil-1-4t-motorcycle-oil

 

There is no question the use of leaded fuel is a problem for the plane...the oil change intervals are half when using Mogas, and the major  maintenance interval on the gearbox is twice as long as when using Mogas.

 

When the new formulation of Aeroshell came out a few months ago, Rotax changed their guidance, stating the new formulation of Sport Plus 4 is now the recommended oil for all fuel types and situations.

 

You can still use Mobil 1 4T if you want, and it's still an approved/allowed oil, but it's not the Rotax *recommended* oil, even with 100% MOGAS.  

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It's helpful to ask why Rotax changed their guidance, was it wrong before or are they simplifying things?

 

If your CT has marginal oil cooling and you can avoid lead I think the 4T is likely the best or one of the best choices.

 

My understanding is that Rotax worked closely with Shell to come up with the new formulation, optimized for the 912 engine.  When they were done they decided it was a good enough blend that they went ahead and made it the recommended oil for all conditions and fuel types.  

 

Nothing wrong with Mobil 1 or another synthetic, it's just a matter of how much credence you put in manufacturer's recommendations.  

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Nothing wrong with Mobil 1 or another synthetic, it's just a matter of how much credence you put in manufacturer's recommendations.  

 

credence in prior recommendations vs current recommendations?

 

There is such a difference between 100LL and unleaded that I give more credence to prior recommendations that took this into account.

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Everyone recommends a specific brand of consumable for their product...Cars, washing machines, dishwashers, etc....  It's a commercial relationship.  That relationship doesn't necessarily equal "better".  In other words, it's advertising. 

 

The 4T is an approved oil and it works great (with mogas only).  The Areoshell is also an approved oil, but they just have a commercial relationship with Rotax. 

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Everyone recommends a specific brand of consumable for their product...Cars, washing machines, dishwashers, etc....  It's a commercial relationship.  That relationship doesn't necessarily equal "better".  In other words, it's advertising. 

 

The 4T is an approved oil and it works great (with mogas only).  The Areoshell is also an approved oil, but they just have a commercial relationship with Rotax. 

 

The 4T was an approved oil according to Rotax documentation.

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The issue with continuing to use the old oils from prior SBs, is that if they change formulations, you won't know until you have problems with your engine. If you look at old revisions, the list of oils which is no longer recommended has a few in it.

 

There is definitely something different with the new aeroshell sport plus 4. The old oil always had a mildly sweet smell to it and I always liked that, but this new formulation smells burnt... :-(

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What I find so interesting about Rotax discussions is that prior to the new oil recommendation, lots of people said "these engine routinely run way past TBO… these engines are bulletproof".  Now that the new oil recommendation has been made, the previous oil recommendations are radioactive and running your engine on anything other than the red bottle is like playing the lottery.  Do ya feel lucky?  

 

We hear about how Rotax worked with Shell to come up with the new oil.  So, were the previous oil recommendations just speculation by Rotax and Shell?  Is the engine so oddly different from other internal combustion engines that it needs an oil that didn't exist before the red bottle?  Was the engine not as good as everyone said it was before the new oil was put into the tank?

 

Rotax and its oil recommendations remind me of the old Soviet Union.  Time to remove the old page from the history book and past a new page in its place.  

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Misunderstandings about our oil selection and its use:

 

The current SI dated 4-2015 addresses fluids. Rotax only recommends Aeroshell Sport Plus 4 and it is not an absolute. They can not test and keep up with varying oil MFG's changing formulas. If an oil is made here in the US and made over seas it most likely has a different additive package. Rotax just simplified things by recommending Aeroshell. This is a controlled fluid for them because it is only made in one place in the world. In England. Aeroshell offered to work with Rotax (no other company has) to develope solely for the Rotax engine that supplies 80%+ of the worlds light aircraft engines. If there is any discussion about formula change Rotax is involved. After a few years Aeroshell decided to check how the oil was performing and then embarked on a 4 year research project with some high time flight schools to further tweak their formula. The engines with high time hours were then taken apart for evaluation. The base stock and additive packages were slightly changed to better enhance the longevity of the engine. Since Aeroshell is hard to come by in some parts of the world and knowing that there are other decent motorcycle oils out there Roatx knows these oils may be used. That said there have been some oils that have proved not suitable for the continued long term health of the engine. Right now Mobile One 4T is under investigation. I don't know any more than that and was informed by Rotech of this development.

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What I find so interesting about Rotax discussions is that prior to the new oil recommendation, lots of people said "these engine routinely run way past TBO… these engines are bulletproof".  Now that the new oil recommendation has been made, the previous oil recommendations are radioactive and running your engine on anything other than the red bottle is like playing the lottery.  Do ya feel lucky?  

 

We hear about how Rotax worked with Shell to come up with the new oil.  So, were the previous oil recommendations just speculation by Rotax and Shell?  Is the engine so oddly different from other internal combustion engines that it needs an oil that didn't exist before the red bottle?  Was the engine not as good as everyone said it was before the new oil was put into the tank?

 

Rotax and its oil recommendations remind me of the old Soviet Union.  Time to remove the old page from the history book and past a new page in its place.  

 

For my part, I certainly didn't mean to suggest that the old recommendations are completely invalidated.  However, it's a pretty reliable bet that the recommendation changed for a reason.  

 

That reason could be economic (Rotax and Shell greasing each others' palms and agreeing to the change), technical (Rotax and Shell found that the new formulation actually works as well or better than any other tested semi- or full synth oil under any conditions), or some combination of the two.  We can guess at that reason(s), but it's really just a guess without further guidance from Rotax.   

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What I find so interesting about Rotax discussions is that prior to the new oil recommendation, lots of people said "these engine routinely run way past TBO… these engines are bulletproof".  Now that the new oil recommendation has been made, the previous oil recommendations are radioactive and running your engine on anything other than the red bottle is like playing the lottery.  Do ya feel lucky?  

 

We hear about how Rotax worked with Shell to come up with the new oil.  So, were the previous oil recommendations just speculation by Rotax and Shell?  Is the engine so oddly different from other internal combustion engines that it needs an oil that didn't exist before the red bottle?  Was the engine not as good as everyone said it was before the new oil was put into the tank?

 

Rotax and its oil recommendations remind me of the old Soviet Union.  Time to remove the old page from the history book and past a new page in its place.  

 

The Aeroshell Red oil is a new formulation that allegedly improves what the old oil did for Rotax engines using 100LL.  I don't see an inconsistency in that evolution.  

 

But new owners should know that if you burn Mogas exclusively (and if occasionally use 100LL use Decalin to treat the ill effect of the lead) then you can double your oil change interval AND be able to use the full synthetic Mobil 1 4T motorcycle racing oil.  Both the fuel and the oil are superior for Rotax over the leaded/Aeroshell treatment.

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You should not try to tweek mixing or tracking your fuel if you want to go to the 50 hour oil change interval.  You can burn all Mogas by investing in a fuel trailer, or a fuel transfer tank for a pick-up truck.  Some also hand fill with jerry cans but that has to be a pain in the rear.

 

When getting fuel away from home you can use 100LL but you need to zap the lead with TCP.  Decalin Runup is good for that purpose...you can take some with you on trips.  http://decalinchemicals.com/products/decalin-runup-fuel-additive/

 

Use 91E10 premium grade gas.  And switch to all synthetic Mobil 1 4T motorcycle racing oil which can be bought at Walmart.  Make sure you always use Rotax oil filters...they are designed specifically for the engine.

 

Here is a picture of a fuel trailer I built for the purpose:

 

 

Both the fuel and the oil are superior for Rotax over the leaded/Aeroshell treatment.

 

Can you provide data to back up the assertion that Mobil One 4T is superior to Aeroshell Sport +4 for mogas use?  It might be, but without specific data directly relevant to the Rotax 912-series engine, then:

 

 

It's fine if you prefer and want to use the Mobile One oil, but you shouldn't make blanket statements on how it's "superior" unless you back them up with real analysis in these engines.  As Roger stated, with the Aeroshell product, Rotax did the running hours and engine tear downs to support their recommendation.  Mobile One may be the best thing since ice cream, but without the data to show that, it's just speculation.

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