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Fuel type...

Guest Tom

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What kind of fuel do you use on Rotax 2 stroke. I had conflicting


claims of one school saying do not use anything but premium unleaded


and anything else will destroy the engine while the other school said


exactly the opposite that premium will destroy head gaskets etc and i


should use only standard unleaded.


Please help clear the confusion.



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Guest TOSGcentral

Hi Tom,


For what it is worth the following notes may help and you can draw your


own conclusions from them. I am certainly not going to come down hard


and say do this and that or else!


I operated Thrusters with R582s in primarily hard circuit training work


over a ten year period. I evolved over three main fuel types – but note


that I was always careful with the correct fuel/oil mix and only


operated with top quality 2 stroke racing oils (primarily


Castrol TTS [synthetic] and what was Castrol 2T but they have changed


the name [mineral] – but never mixed the two oils!


Low Lead Petrol. I used this without drama for many years but the


product appeared to deteriorate over that time period. This was


particularly in the areas of fuel filter contamination and steadily


escalating engine operating temperatures (probably from the various ‘shandy [admin removed obscenity]tails’ that started being used.


100LL Avgas. This became available on the airfield and I switched to


this mainly for contamination control reasons. I was appearing to get a


good run out of it, operating temperatures went down, power went up and


contamination cleared up. However I was very lucky.


The chance failure of an oil/water seal on the transverse water


pump/rotary valve drive shaft caused the engine to be pulled down.


Richard Eacott of Boonah does all my major engine work and I comply


exactly with his advice – he is very competent!


Richard called me in to take a look at the stripped motor and advised


me to get off the Avgas! The engine only had about a 130 hours on it (I normally get about a 1000 hrs out of a R582).


The combustion chamber and piston crown were sludged up with lead


deposits and this had started working down the barrels and piston


rings/sides. Damage was already being caused to all three! We saved the


motor by catching it in time – but it was pure chance!


Premium Unleaded. I then switched to this product and have had no


problem with it. I get good operating temperatures and power. My main


control however is still fuel contamination! I probably pay top dollar


for my fuel because I use only outlets that I know buy in kosher fuel,


do not shandy, have clean storage tanks and use good quality




Conclusion. Other than the Avgas incident mentioned I cannot comment on


fuel ‘destroying engines’ or taking out head gaskets etc. I am also not


offering advice, simply an account of what I found and consequently


what I personally do – and I am a reasonably conservative and careful









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Thanks Tony, you've certainly shed some light on the subject. When it comes to premium do you use any specific brand (ie Shell Optimax)?







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Guest TOSGcentral

I use BP personally because that is available locally at a good quality


outlet and also because a close friend is one of the senior 'hands on'


production people at a BP refinery so I get the 'inside running' on a


lot of things!


Note for Ian: The 'keep it clean' device you use on this forum is a bit


picky mate! Good job the forum is not about chooks although I suppose


rooster would do! And my wife will have to be careful obviously about


ordering exotic drinks - she may be misunderstood



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Guest howard

The subject of the gummint possibly permitting a stealth blend of


ethanol was discussed at the BM. Tech are very worried about the effect


on seals and I think members should be raining their concern to have


tech take the matter up with the gummint.



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I'm running an INVERTED 582 and used to run on unleaded mogas.I


was fortunate that I was rebuilding my plane during the time of the


fuel adulteration problems but did find the odd problems starting and


often had fouled plugs running ULP.Combine this with using


Avgas at one of the Nat-flys and on the way home I started getting some


overheating and what sounded like detonation!?On landing at Bathurst to refuel my plugs were completely fouled, so after refuelling with ULP and some new plugs I got home OK.I now run PULP (Caltex 98 if possible) and my motor runs like a clock.I have only used Castrol Super TT, and now use it's replacement Active 2-T, I may try a synthetic one day.Arthur.



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My 912 powered Drifter has only ever been fed BP or Shell (usually BP) premium unleaded mogas.


I have no complaints at 406 hours. Clean plugs and smooth running.


One 912 owner swore to me that nothing but Optimax would ever suffice.


Another 912 owner told me NEVER under any circumstances to use Optimax.


Who do you believe????


I wish I could find a REAL authority on fuels.





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I know this isnt directly aircraft related, but my bike (a 250 cc 4 cyl 4 stroke, running to 19,000 rpm)


i only use Premium ULP in the bike, but i will never use Optimax.


general consensus in the bike world is Optimax is a no no. no idea why,


it just gums up injectors, i have ever only used BP or Mobil premium,


and no sign of pinging or anything for that matter all the way to


19,000 rpm.


Yet others will say Otimax is great in their car, im not sure if its


the fuel, or the way its handled at some distributors, butit always


seams to be brilliant, or dud fuel, never in between.



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I have asked Wal at Bert Flood about th 10% ethanol in PULP (it is starting to turn up in the Canberra area, but not by stealth yet as far as I know)


two weeks ago. He was going to try and get some info from Rotax, but I


have heard nothing yet. I run a 912 ULS and try to use PULP that does


not block the filters, all seem to do it to a greater or lesser extent,


but I have not knowingly used 10% ethanol yet.


What is the concensus on this stuff? I know it will probably vapour


lock sooner due to the higher vapour pressure, but does it affect the


engine in any other way? If ALL PULP goes this way, is Avgas usable in


the long term?





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With the 10% being pushed by the powers that be, is it a requirement


that fuel containing up to 10% be labeled as such? If not, how are we


to know if it has it in? The servo staff most of the time just look





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Ethanol has an 'octane' rating (or more correctly, 'a performance number') of about 113.


Unlike petrol. ethanol has an affinity to water which is quite readily absorbed.


It is a solvent which cleans fuel tanks and lines and blocks filters. Some flexible fuel lines are badly affected by ethanol.


Ethanol contains less energy per volume than petrol and requires a


richer mixture to avoid detonation due to localised overheating, which


can burn neat little holes in pistons. As a rough rule-of-thumb


doubling of jet sizes in a carburettor would be a good starting point


if you were running pure ethanol.


I suspect vapor-locks could be a real problem in aircraft.


Ethanol is an OK fuel in a motor and sustems designed to use it.


In summary, any amount of ethanol in aircraft fuel could spell trouble. Why risk it?





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Guest micgrace



Heres aquick and dirty method to ckeck for presence of ethanol in bowser fuel.


grab a glass container, fill it 1/4 full with water, mark the level. (bottom of meniscus)


Then fill up with the fuel sample, shake and let sit.


Note the rise of the water level (if any) If none safe to use. (not the sample) If it rises don't use this in an aircraft regardless of octane rating.


I believe some fuel companies make use of ethanol to raise the octane rating, so beware. (They don't tell us)




ethanol contains at least some water, you can be sure of corrossion


occuring somewhere in the fuel system. It has dire effects on


magnesium/aluminium castings as found in most carbies. Simple to see,


just take a carby off a car / motorbike that's been sitting for a


while. There will be a whitish deposit ready willing and able to ruin


your day.


How much more so for an aircraft that may sit around for months on end.


Actually if the aircraft is going to be sitting around for a while, it might pay to inhibit it for storage


All for now.


Micgrace. It's what you don't know, that will get you.



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Guest ozzie

i think the reason a lot of people who don't like optimax are from it's


effects on plastic and paintwork. older engines would suffer from seal


and fuel system problems. there also seems to be a bit of a competition


between fuel companies over who has the highest octane rating. the


aromatics used in optimax seem highly corrosive compared to other fuels


in the same rating. ethanol has been around for ages, it has been used


for years in sth america. for the best info on it's use and precautions


go to the local speedway track and talk to the bikers there. they blend


there own racing fuels so they would have some good knowlege on the




some things to consider when using unleaded fuel in engines that are


NOT fitted with a catalitic converter. and carbon filter on the tank


vents. the fuel in both it's vapor and burnt form is highly casogenic (cancer producing) do not use this fuel for parts cleaning, hand washing.


make really sure your cabin is exhaust free. stand upwind of your


whipper snipper exhaust. things used to be so reliable in the good old


super days, hey. ozzie



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Guest micgrace

Re: Fuel with ethanol


There is a real danger using fuel with ethanol in aircraft. The simple fact, is that ethanol is hydroscopic (will absorb water)


Those using the engine (car / bike /whatever) every day will probably not have a problem.




overnight, the nice warm fuel in the fuel tank will cool, the outside


air will enter the tank, and more water will be able to find it's way


into the fuel (ethanol).


Which brings up another point, refuel at the end of flight for the day, unless putting the plane into storage (other methods req.)


And as everyone knows water = corrossion, athough, aromatic hydrocarbons (hydrophobic) as in fuel are not corrosive to aluminium as far as I know.


Remember the daily GA ritual of checking for water?? This should be done on our aircraft as well.


As for me, I've got no intention of finding out for real.


All for now, Micgrace


What you don't know will get you, I'm still learning



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  • 3 months later...
Guest Kitfox 4004



all very interesting and I would say pretty correct. I'm no expert to judge but I'll throw in my two bobs worth. I used to race Karts and in some class's we ran on methanol. Methanol, Alcohol and Ethanol are much the same. Methanol as I understand it and according to a book I have is wood based and Ethanol is grain based as I rememmber it. Anyway that part is accademic. So what I learnt was that Methanol absorbs moisture and as stated this corrodes aluminium etc and rusts steel. It can swell up paper in fuel filters so they stop passing fuel.


Now as I run a Rotax 582 two stroke I'm dead worried about even just 10% Ethanol as what was happening when using Methanol in Kart motors was pin spots of rust on the needle bearings and lot's of failures unless we ran petrol through the motor afterwards. We had to screw in our mixture screws to do this.


Also be aware that as good as Synthetic oil is it also absorbs water. Run the motor regularly like every day and it's fine but let it stand and you can have trouble. Sounds strange but it's true. Oil companies often make a 50/50 mineral synthetic blend to address this problem.


Back to the 10% ethanol in petrol. I own a Kitfox and so spend heaps of time on the Matronics Kitfox list. On that list there has been lots of dicussion re this 10% ethanol wrecking our fibreglass fuel tanks. So that's another point. It gets to a lot of fuel lines too !


Re two strokes and Avgas. Apart from Tony's observations be aware that the lead will foul the plugs in fairly short time although one tank to get you home should not be a problem.


Hope all this is helpfull,





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Guest micgrace



From my chemistry information, ethanol/methanol is about the same acidity as water. And everyone knows what effect water has. Put the 2 together, and the alcohol actually partially ionizes. This effect is used in organic chem to create some useful compounds.


my 2 cents worth, micgracesmiley1.gif



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  • 3 weeks later...

I have been told on several occasions the fuel companies pool their resourses. For example in Tasmania, all fuel comes in on same boat. fuel companies them draw from the one source. They say they tip in their own additivies which makes each unique..????


I was led to understand 98 ron fuel was produced in each location (WA, Melb, Brisbane, Sydney by a singlecompany at thatlocation and distributed to each company (just like the Tassie example).


Before we get excited if BP, Shell is best, perhaps we need to clear up the source of each individual fuel.


In my opinion, as Tony Hayescorectly stated. the main difference is if the fuel is a shandy, and how it is cared for (filtration, water contamination etc) on the service station site.


I have used 98 Ron, (mainly shell) for 300 hours in a 912s rotax with the occasional Avgas when I can get it. to date had no problems with fuel filters checked regulary, and on most occasions clean as a whistle.


I'm more paranoid about static filling from plastic and metal cans via a siphon...... I think it is a little safer than tipping in via a funnel. any comments??







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  • 1 month later...
Guest palexxxx

I have found the following article about the use of Mogas (auto fuel) and Avgas in Rotax engines. I hope it is of some use.




Avgas vs Mogas for the Rotax 912 and 914 series aircraft engines Fuel for the Rotax 912/914 series engines is a topic that has been discussed and questioned for many years. Aviation articles from the early days of the 912 added to the confusion by stating that the Rotax, like the Continental and Lycoming, need lead to protect the valve train. Not true! The engine was designed for unleaded auto gas(Mogas); it will also run very well on Avgas, but it does not require it! However, there are some issues with Mogas and Avgas that we will discus and must be considered for your application:




While Avgas is heavily controlled, there is not a worldwide standard for Mogas. In some developing countries that have to import most of their oil, but they have lots of farms to grow grain, auto fuels contain more that 20% ethanol and are of questionable octane. In North America there are many states that have mandates under the EPA that forces producers to have at least 10% ethanol by volume in auto fuels.


Fuel ratings


The engine is designed by the engineers for normal auto gas that is available in most countries. Rotax uses the fuel specification that is called RON (Research Octane Number); this is only one method of measuring octane. One other method is MON (Motor Octane Number) and is essentially the same test but for a higher speed rating. In each case the test fuel is subjected to a test engine that uses a variable compression ratio engine. This fuel is then run in a prescribed test and the results, knock point of the engine, is noted. Canada and the USA use a combination of the RON and MON rating added to together and then divided by 2 for an average. This average, or AKI, anti-knock index, is what is normally seen advertised for the fuel octane. From this information a rating can be assigned as to the octane of the fuel. Octane is by definition the ability of the fuel to resist detonation by pressure and heat. This means the higher the rating the more resistant to detonation. Fuels can be designed in various ways to accomplish this, let us look briefly at them.




Lead, a heavy metal, can be added to the fuel to increase the octane. This is still, in aviation, the normal way to increase octane. It is unfortunately very hard on the environment and has been removed in most automotive fuels due to the pollution of the environment. The highly recognized 100 LL fuel in use today in the US is 50% of the lead volume of the fuel it replaced, 100/130, from the old days. This 100LL is still much higher in lead that any of the leaded auto fuels that were used in years past. The problems with the leaded fuels are the pollution and the heavy deposits of lead left on the spark plugs, piston rings, oil passages, and cylinder heads. Fuels with lead can be used if the operator is willing to increase maintenance on these parts. In many cases the engine will require a top overhaul well before the TBO due to the lead contamination. Additives that help purge the lead, TCP for example, are beneficial, but, are not yet recommended by Rotax due to the volatile nature of such an additive. The Rotax liquid cooled head is also a problem with a lead enhanced fuel. In simple terms it runs too cold. The head never gets hot enough to allow the lead to “purge†itself of the deposits and they build up over time. In comparison, an air cooled head has massive heating and cooling cycles that keep lead contamination more under control.


It’s interesting to note that 100LL aviation fuel is the single biggest source of airborne lead pollution in North America, yet more fuel is consumed by cars in one day than all of general aviation uses in one year! No wonder the environmentalists would like to see 100LL phased out! Due to its low volume and extra handling expenses even the fuel manufactures would not bemoan the passing of 100LL.




Ethanol, a grain alcohol, is the most common way to increase octane in fuel and replace lead. The grain used is readily available and for many countries this can supplement poor fuel supply and increase economic benefits for the grain producers. When the US and Canada went to unleaded fuels the problems of the ethanol were addressed by combining it in a stable additive called MTBE. Ethanol by itself will absorb huge volumes of water given the right circumstances. The solution was a simple chemical combination with other material. The problem now is that if fuel containing MTBE, which has been in auto fuels ever since we went to unleaded gas, is that this stable additive does not dilute when it gets into the water table. The result is that MTBE is now being removed and replaced with increasing amounts of straight ethanol. How much is too much? Rotax has issued statements that you should not use more that 5% alcohol by volume in any fuel. This would be nice but it is simply not practical. In the US for example the average percent by volume is 10% and this is controlled by the state, EPA, and other agencies that do not care how the engine manufacturer mandates his requirements. We know that the country of your application will vary worldwide in respect to alcohol in the fuel.




Methanol should never be used in aviation engines fuels due to the corrosive nature of the alcohol. Octane boosters Test done by independent labs show that octane boosters have little value to the consumer. The controlled tests concluded that while the booster is advertised to increase octane by up to 7% the octane increase was actually found to be a measly 1-2% and some brands actually had a negative effect on the octane. The conclusion is that, economically and performance wise, you are much farther ahead to just buy a higher grade of fuel.


Mixing Avgas and Mogas


Any ratio of Avgas to Mogas is allowed. A surprisingly small amount of lead will increase the octane level of Mogas.


Avgas and oil types


Warning! Avgas and fully synthetic oils do not mix! It was found that the fully synthetic oils are unable to capture the lead and carry it out of the engine at subsequent oil changes. The result is the lead accumulates on the spark plugs, piston rings, valve guides and generally throughout the engine. In some cases the fully synthetic oils would cause the lead to form a thick paste that would plug oil galleries and even the oil cooler! If you must use Avgas then use mineral or semi-synthetic oil and change the oil more frequently. 25Hr oil changes and premium oil will still be more cost effective than added engine maintenance due to excessive lead contamination.




Storage of Mogas should be avoided if possible. As we previously discussed, Ethanol will absorb huge amounts of water and must be protected from possible condensation conditions. The lead in Avgas and other chemicals in unleaded fuel are photosensitive, and will dissipate if they are exposed to the sun. Avoid keeping winter Mogas into the warmer months. Keep any container tightly sealed to prevent evaporation.




Exhaust gas temperature can be a useful tool, especially if you must use an alcohol additive fuel. As long as you are under the 10% by volume you can simply adjust the carbs to accommodate the different burn of the fuel. Ethanol fuels will burn hotter, due to the decreased density of the fuel, than aviation fuels. You may have to enrichen the jetting to accommodate the fuel.


What should I use?


Your airframe manufacture has the finial say on fuel requirements for each particular installation. We know from the engineering standpoint what Rotax needs. Check your operators manual and it clearly states which fuel is required. Now you need to find out what fuel you have available to you. (Is it RON or MON rated)? If the fuel is over 10% alcohol, measurable, then do not use it. Go to a low lead aviation fuel with the octane that is suitable. We know from experience that if the octane is too low, you detonate and could possibly fail the engine. If your fuel is aviation rated 100, no problem, the octane is high enough. If the fuel is auto rated, check the RON rating and compare to the Rotax information. An EGT for all installations is advisable because it monitors the actual temperature that the fuel air mixture is producing



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Guest palexxxx
I have found the following article about the use of Mogas (auto fuel) and Avgas in Rotax engines. I hope it is of some use. Peter.



Could you supply source for this article please.






I found the article at the following forum,




then click on 'Rotax 912', then 'Engine use of fuels'





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  • 2 weeks later...
Guest palexxxx

Further to the info that I posted above re avgas vs mogas:


I have found some more info which you maybe interested in.


Feeding your Rotax 4-Stroke Aircraft Engine


Fuel | Engine Lubrication | Oil Filters | Cooling Liquid | Spark Plugs




Octane rating


The Rotax 912 A/F/UL engines require a minimum octane rating of 87 AKI, commonly referred to as "regular" while the Rotax 912 S/ULS/ULSFR and 914 F/UL require a minimum of 91 AKI ("premium").


Some may have noticed that the Rotax manuals mention ratings of 90 and 95 respectively. These ratings are calculated based on the RON standards used in Europe and are equivalent to a rating of 87 and 91 under the AKI standards used in Canada.


In all cases, we recommend using as high an octane rating as possible, since fuel evaporates and quickly loses its octane rating by osmosis when it lays in your aircraft's fuel tank or in a plastic jug. A "premium" fuel will see its octane rating reduced to unusable levels after as little as three weeks. Fuel with a lower octane rating would obviously have an even shorter usable life.


Too low an octane rating will cause pre-ignition and detonation which can damage the piston ring grooves, skirt and crown.


Where to buy


It is recommended to buy gas at the busier gas stations of the major oil companies, since their tanks are renewed often allowing the fuel to stay fresh and clean.


Aviation Fuels


It is possible but not recommended to use 100LL AVGAS, since the the lead content is like cholesterol to your engine: it will accelerate wear on the valve seats, create deposits in the combustion chamber and sediments in the lubrication system and gearbox. Increased maintenance is necessary to compensate. Unlike "conventional" aircraft engines, lead is absolutely not essential to the proper lubrication and operation of a Rotax 4-stroke aircraft engine. The increased octane rating also has no marked advantage for the operation of your engine.


To be avoided:


* "Regular" fuel except if used in the 912 A/F/UL and burned entirely on the day of purchase;


* "Premium" fuel which is more than 3 weeks old


* AVGAS except when the required automotive fuel is not available


Engine Lubrication


Oil Specifications


Rotax recommends using a high quality, major brand, 4-stroke motorcycle oil with gear additives and “SF†or “SG†API classification.


The gear additives are required to withstand the high stresses in the reduction gearbox. The “GL4†or “GL5†specification is recommended.


Oil Types


Users running mostly unleaded fuel can opt for full-synthetic or semi-synthetic oils. Users running leaded AVGAS more than 30% of the time should only use mineral or semi-synthetic oils, since a full-synthetic oil will sludge and create residues when used with leaded fuel. Oil changes and other important maintenance tasks have to be performed more often when using leaded fuel, as described in the maintenance tasks table.


Figure 1. Selection of oil viscosity based on climatic conditions.




A multi-grade oil is recommended. Refer to figure 1 to select the appropriate viscosity for your climate.


Further Reference


Rotax has published a Service Instruction document titled "Selection of Motor Oil and General Operating Tips (SI-18-1997 R5)". It contains a list of suitable oils and unsuitable oils. Bear in mind that these tests were based on a selection of oils available in Europe. These oils may not be available in Canada, or the oils available under the same designation in Canada may not use the same formulation as their European equivalents. Also, oils only available in North America are not included in this list.


* SI-18-1997 R5, Selection of Motor Oil and General Operating tips for Rotax Engines Types 912 and 914 (series)


To be avoided:


* Synthetic oil if you run leaded fuel more than 30% of the time


* Oils with friction modifier additives ("antifriction"), will cause the slipper clutch to slip


* Oils designed for "conventional" aircraft engines


* Oils designed primarily for diesel engines as they generally have insufficient high temperature properties and additives which can cause friction clutch slipping


Oil Filters


Only the Rotax-recommended oil filter (part 825 701) should be used. Only those filters assure the correct pressure for bypass valve operation. Other filters have less filtering surface and are not made to withstand the high oil pressures the Rotax 4-stroke engines operate at.


To be avoided:


* Any other filter than Rotax part 825 701. There are no equivalents or substitutes!


* Contrarily to what some rumours would like you to believe, Rotax does not authorize the use of any other filter!


Cooling Liquid


Type selection


The 2004 release of Service Bulletin "Change of coolant specification (SB-912-043 / SB-914-029) has created some confusion among owners. The instructions it contains are fairly simple but require referring to a few manuals for full comprehension. Here is a more concise explanation:


Figure 2. Cylinder heat temperature limits based on type of coolant and radiator cap in use.


The selection of your cooling liquid depends on the efficiency of your cooling system (radiator size and installation, etc).


Cylinder head temperature (CHT) is directly related to the efficiency of your cooling system and to the dangerous presence of vapour bubbles. Therefore this temperature is measured instead of the cooling liquid temperature.


If in all situations your cylinder head temperature is inside the limits of the "hot" or "normal" ranges of the first two columns in figure 2, you may use the ethylene glycol and water type.


You may notice that systems using a 1.2 bar / 18 psi (standard on recent engines) radiator cap have a broader range of allowable temperatures than those using a 0.9 bar / 13 psi cap.


If however your cylinder head temperature reaches the "hot" range of the third column, the use of Evans NPG+â„¢ non-aqueous (waterless) liquid is mandatory.


Ethylene glycol type


Rotax recommends a mix of 50% long life antifreeze concentrate without sulphates and phosphates, with anticorrosion additives designed for aluminium, and 50% distilled or demineralised water.


Do not forget to renew this cooling liquid every two years.


Non-aqueous type


The Evans NPG+â„¢ non-aqueous cooling liquid is mandatory under certain circumstances, but we recommend it for every engine since it offers more efficient cooling, an extremely high boiling point, a very low freezing point, corrosion prevention and unlimited life (no need to renew every two years). Also notable is that it operates at no or minimal pressure which greatly increases safety in case of an in-flight leak. It is available from us.


To be avoided:


* Antifreezes containing phosphates and sulphates, even those which are low phosphate and sulphate


* Water which is not distilled or demineralised


* Mixing ratios other than 50:50


* Ethylene glycol type of coolant if the appropriate limits can be exceeded


Spark Plugs


Plug Type Socket Electrode Gap


912 A/F/UL NGK DCPR7E 16mm 0.7-0.8mm/.028-.032â€Â


912 S/ULS/ULSFR NGK DCPR8E 16mm 0.7-0.8mm/.028-.032â€Â


914 F/UL NipponDenso X27EPR-U9 12mm 0.6-0.7mm/.024-.028â€Â


To be avoided:


* Other spark plug models, including those with a different heat range code, and other manufacturers' equivalents


* Unverified spark plug gaps. Always check gap before installing!



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  • 6 months later...
Guest disperse

just to add my little bit .......the idea that 98 octaine fuel produces more energy (still being debated ) is the reason some people say don't use it in small engines.....more stress others believe that the cleaning agents doing there job is the reason for the better economy......i dont know ....in my bike i would notice a difference......91 octaine = reg / 95 = premium / then the 98's = the premium premium



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