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Mixing UL91 / 91UL and 100LL, and need for additive LW-16702, or Aeroshell 15W/50

I wonder what’s the basis for oil with lycoming anti scuff additive being equired.

I’m not aware of such a requirement when mogas is used.

Do conti make a similar request,?

Administrator
Shoreham EGKA, United Kingdom

Flyingelephant

We have the 91UL fuel tank placard for the Robin DR400 and can make these without too much trouble. I will see if our team has the time to manufacture placard’s for other types and post further when I have investigated this.

What aircraft type would this be for ?

Bathman wrote:

I wonder what’s the basis for oil with lycoming anti scuff additive being equired.

I’m not aware of such a requirement when mogas is used.

The lead in 100LL contributes to the lubrication. (Of the valves?) When there is no lead, an oil additive is necessary.

Lycoming Service Instruction No. 1070AB (or later revisions), “Specified fuels”, states: “CAUTION: … WHEN USING THE AUTOMOTIVE FUELS IDENTIFIED IN TABLE 2, LYCOMING OIL ADDITIVE P/N LW-16702, OR AN EQUIVALENT FINISHED PRODUCT SUCH AS AEROSHELL 15W-50, MUST BE USED.”

So there is indeed such a requirement with MOGAS.

Last Edited by Airborne_Again at 11 Jun 08:07
ESKC (Uppsala/Sundbro), Sweden

Airborne_Again wrote:

The lead in 100LL contributes to the lubrication. (Of the valves?) When there is no lead, an oil additive is necessary.

There are a lot of experts, like Mike Busch, who say that this is an OWT. The recent fiasco with the UND fleet that reported “valve seat recession” has challenged the experts to also look at that possible scenario. What’s good about these discussions is that we will better understand the risks and rewards of running unleaded.

I recall all the same discussions in the 1970s when we got rid of leaded automobile fuel in the US – everyone was sure that the sky was falling, but it still seems to be there, thankfully.

As a data point, I mix mogas, UL91, and 100LL regularly. No issues so far. I have stopped hauling jerrycans of mogas to my hangar, mainly due to laziness, but also to support my local flying club with fuel purchases of UL91. I only burn 100LL when traveling and the airport only has leaded fuel.

Fly more.
LSGY, Switzerland
Now when talking about lead in gasoline – think about Diesel or gas (methane ) engines. Never had lead in the fuel but certainly you need good quality valves and seat rings .And these engines do a multitude of high power operating hours at minimum oil changes compared to hobby aero engines that are run at max. 75 percent power. That setting means maybe 2400 rpm only , not much more than idle for modern engines. Oil additive for unleaded fuel, sure , another BS in aviation business, write aviation on the product for selling anything to worried pilots. Vic
vic
EDME

vic wrote:

Oil additive for unleaded fuel, sure , another BS in aviation business, write aviation on the product for selling anything to worried pilots. Vic

Maybe Lycoming has a secret deal with the oil companies, what do I know? But do you really use less costly automotive oil in your aircraft engine as aviation oil is only for worried people?

ESKC (Uppsala/Sundbro), Sweden

Actually we use straight SAE 100 oil in the radial, no additives at all and super 98 . The engine was run like that all the time we were told by the seller. But really I cannot see any benefit from oil for valves and seats. Any little oil used by the engine will be burnt once it passes the exhaust valve, the intake valve is never a problem anywhere. But the matter is worries about leadfree fuel and “special” oils for that operation. Think about Rotaxes, Diesels, V 8s , Porsches , all run on unleaded , some at much higher loads, no special oils there. Just the steel for valves and seats has to be suitable, like stellited ex valves and high chrome steel seats.

Vic
vic
EDME

I have no dog in this game (burn 100LL because there is no 91UL anywhere I go, and use 50% W80 and 50% 15W50) but the problem with empirical data is that

  • we have too little data posted by aircraft owners (Europe has relatively few owners who participate on forums and fly a lot)
  • a given pilot might be repeatedly flying a particular mission profile which sidesteps an issue (e.g. flying at a particular power setting)
  • a given pilot might be repeatedly flying a particular mission profile which exhibits an issue but he is unaware of it (the vast majority of owners take little or no interest in their maintenance, and the vast majority of maintenance people know next to nothing about operational issues)
  • only some engine models may suffer from it, and be under-represented on forums

Anyone involved in manufacturing anything nontrivial will be familiar with this You can sell 100k of some product which has a serious defect but it is never discovered because 98% of the users never make use of that feature, another 1% are in the Peoples’ Republic of Upper Volta and are too poor to pay for return postage, and the final 1% are in Germany, have quietly chucked it in the bin, and bought a replacement from Siemens

Administrator
Shoreham EGKA, United Kingdom
Power settings may not matter much as cruise is rarely 100 percent power with most pilots here. So octane rating or lead content is only critical in climb at maximum revs – which is only 2500-2700 on most engines here. Niot much different to turboed truck Diesels today , unleaded. One thing to watch is water content in non-aviation gasoline when flying in freezing temps, but then , you can have that in avgas as well. There must be checks for water in fuel when filling up from unknown brands. Some do lots of endoscope checks, even with avgas only. Any bad effects from unleaded would be detected from seat wear, valve clerarances no means for getting numbers with hydro tappets – would not want them. Vic
vic
EDME
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