Car fuels vary greatly and on the whole Europe seem to have better quality auto fuels than us in Australia.
In Australia there seems to be 3 main brands (they each blend their fuels in slightly different way). Three of the main suppliers here are Caltex (originally off shute of Chevron), BP and Shell/Liberty (now Viva energy). Caltex blends tend to keep there volitility better than BP and much better than Shell but Avgas is all but perfect keeping volitility for 12 months. Rob Thomson had data sheets for Australian auto fuels and even brands varied what they sold up north to down south in Australia. 95 on the hole tend to be a bit more honest fuel than especially Shell 98 but I prefer fresh Caltex 98 if I can get it. If I am burning the fuel on the same say I am less particular. When not using a plane for a while I would always store with Avgas. Each time car fuel goes up and down in the air it can loose some volitiles from solution. Continuous use of Avgas will cause a build up of lead under heads but that's all. Tetra Ethyl Lead is still still a very good lubricant but only need a blend of 20‰ to 25% in fuel as a lubricant and then you do not have to use it every fill. I am quoting Doctor Hodges in Australia who would issue the STC to use auto fuel in most smaller Lycomings and Continentals carb engines. 95/98 here the plugs will always by colour run as if carb is running rich. If you use Avgas your plug colour means more and should be a medium gray ideally. I personally always use timing of 28deg (and somewhere I read it in Limbach paperwork as bottom of range). There is no loss in power and temperatures will usually be lower in climb. One gear tooth equals 3⅓ degrees. Almost zero chance of pinging and including using our rubbish fuels. You may recall Contenintal guess 35 years plus ago universally reduced the timing on their little 85hp engine (Champ aircraft and think Cessna 140) lowered timing to 25deg from think 32deg. Nobody picked any performance loss but DEFINATELY cooler in the climbs and you could maintain a full power climb indefinately. That is my justification for having Limbach timing under the book mean of 30deg. Ian McPhee +61 428847642 Box 657 Byron Bay NSW 2481 Australia On Tue, 4 Feb. 2020, 03:17 , <[email protected]> wrote: > Hi Ric, thanks for the answer. > > we see a dark attack on the valves, it looks like a fine tar-like deposit, > that makes the valve doesn't close properly after a while and we loose a > lot of power on the engine. > > We cannot explain this phenomena, but it caused already 2 times a lot of > motor overhaul. > > Br, Peter > > > ------------------------------ > *From: *"Ric Sutton" <[email protected]> > *To: *"peter clymans" <[email protected]> > *Sent: *Sunday, February 2, 2020 3:57:23 PM > *Subject: *Re: MOGas or AVGAs > > hi peter > i vaguely recall this topic being mentioned several times before on this > forum but my experience is thus- i run 95 mogas when i can. i am often > faced with only having the choice of 98, however i believe that the > volatiles evaporate more readily(in my part of australia at least). not > very good if you are not planning using a whole tank. i have encountered > pinging (detonation/preignition) as a result of this. there is an > airworthiness directive that speaks of the effect of some fuel blends on > the fiber glass fuel tank. performance wise- have noted very little > difference between fresh 98(or 95)mogas and avgas. through some........ > circumstances shall we say, a rebuild was necessay. this was after running > on avgas. on pulling down the engine i found lead deposits every where. is > that a problem? you can decide. > as it was a little while between tearing down and reassembly (6 ish > months) the valve seats were badly corroded. after speaking with people > that know much more than i, i am lead (geddit) to believe that chemical > reactions with some of the additives in avgas may have been instrumental in > this and wouldnt be as prevalent running on mogas. > i have heard of some retarding the timing to settle the pinging. i am > undertaking a protracted exercise to collect vibration data and carry out > some very rudimentary analysis before i commit to the same. > this is my two cents > is there anything specific you are trying to ascertain. > cheers > Ric. > ------------------------------ > *From:* [email protected] <[email protected]> on behalf > of [email protected] <[email protected]> > *Sent:* Saturday, February 1, 2020 5:50 PM > *To:* dog <[email protected]> > *Subject:* [DOG mailing list] MOGas or AVGAs > > Dear all, > > we are flying a Dimona H36 with Limbach L2000 and had a discussion using > MOGas or AVGas. > > Any opinions to this ? > > What are you using currently ? > > Appreciate your feedback. > > Peter Clymans - KAC Weelde - Belgium > > >
