nicks_tr34 Posted December 26, 2008 Report Share Posted December 26, 2008 As title really, do you know if/how the oil is effected by the fuel when mixed? Will both have a reduced lifespan/effectiveness?? I know petrol (unmixed) has a limited lifespan, and bottled oil has one too (the latter being many years, the former can be counted in weeks), but don't know what happens chemically to either component when they are mixed ... Quote Link to comment Share on other sites More sharing options...
feetupfun Posted December 26, 2008 Report Share Posted December 26, 2008 Many years ago when petrol could be stored for weeks and seemed to work well, it was drummed into me that it was important to leave the addition of the oil till the last minute for the best results from the brew. With the pump petrol we get here, it goes to crap so fast that it is now quite irrelevant when you mix in the oil. If straight modern petrol or premix is more than 2 weeks old, it goes into my car fuel tank. Quote Link to comment Share on other sites More sharing options...
tt5th Posted December 26, 2008 Report Share Posted December 26, 2008 Just wondered if anyone could explain to me this whole thing about petrol "going off"? I appreciate pre-mix might go off - particles seperating or something - but I've just started a bike that i bought thats been stood for 2 years and the petrol in it seems fine! I've also never had any problems on any bikes I've had when they've been laid up for months at a time while I try to fix them. That and the fact that the petrol must stay in various storage tanks for months before it gets to the pumps. So yes any info on this urban myth greatly appreciated. I probably should get to bed now, trial in the morning ha! Merry Boxing Day, wish me luck!! Quote Link to comment Share on other sites More sharing options...
jse Posted December 26, 2008 Report Share Posted December 26, 2008 Just wondered if anyone could explain to me this whole thing about petrol "going off"? I appreciate pre-mix might go off - particles seperating or something - but I've just started a bike that i bought thats been stood for 2 years and the petrol in it seems fine! I've also never had any problems on any bikes I've had when they've been laid up for months at a time while I try to fix them. That and the fact that the petrol must stay in various storage tanks for months before it gets to the pumps. So yes any info on this urban myth greatly appreciated. I probably should get to bed now, trial in the morning ha! Merry Boxing Day, wish me luck!! I can probably give a few reasons without going into the geeky chemical analysis area. 1. Evaporation, as the "lighter" chemicals in it (so called high-end aromatics) evaporate, which can also lead to hard starting and poor engine performance due to problems with vaporization. 2. Oxidation, as some of the chemicals react with Oxygen to produce new compounds (which produces that sour odor we all are familiar with and the "gums" that turn the fuel the dark color). 3. Contamination, as temperature flucuations promote condensation and water. 4. Light can also be a problem as gas is photo-reactive and most plastic fuel cans are translucent. There's a few guesses. Jon Quote Link to comment Share on other sites More sharing options...
nicks_tr34 Posted December 26, 2008 Author Report Share Posted December 26, 2008 (edited) I know that one of the reasons fuel goes 'off' is that it oxidises and loses octane. I seem to remember reading somewhere that fuel loses 1 octane point per fortnight of storage. So if you buy 95ron, in 3 months it is essentially 89ron*. Obviosuly you can then run into 'detonation' problems. I am fairly convinced that the fuel goes off with time - especially if it is not in a sealed container (the tank has a breather, therefore not considered sealed) so I am more concerned if adding the 2-stroke makes this situation worse or if the - lets face it quite hostile petrol deteriorates the oil when mixed. My concerns origin:- I also run 2-stroke go-karts, they run a obscene 16:1 castor mix, and even after a fresh mix for the day and leaving the leftover/unused fuel in the fueltank (translucent), you can see the next day the fuel/oil mix is starting to turn orange from clear/slight yellow (castor oil is virtually clear in colour). Certainly a week later and it is red!!! ... That is with castor oil - not sure again if there reacts differently to normal 2-stroke. As I have seen this extremely rapid discolouration, there is obviously something nasty going on in there and therefore I never use the castor pre-mix on anything other than the day of the mix in my kart. Oh and my mate tried using 2-week old pre-mixd fuel in his kart and the thing simply wouldn't run right!!! coincidence??? ... nope, we made a fresh batch and it ran perfectly! - again that is castor if it makes any difference ... Hence my concern for 50:1 2-stroke mix degeneration in my trials bike and the reason behind this thread ... Help!!!! *Don't quote me on those exact figures, but you get the idea! Edited December 26, 2008 by Nicks_TR34 Quote Link to comment Share on other sites More sharing options...
b40rt Posted December 26, 2008 Report Share Posted December 26, 2008 Many years ago when petrol could be stored for weeks and seemed to work well, it was drummed into me that it was important to leave the addition of the oil till the last minute for the best results from the brew.With the pump petrol we get here, it goes to crap so fast that it is now quite irrelevant when you mix in the oil. If straight modern petrol or premix is more than 2 weeks old, it goes into my car fuel tank. I assume your car doesnt have a catalitic converter, cats dont like additives. Quote Link to comment Share on other sites More sharing options...
docheckle Posted December 27, 2008 Report Share Posted December 27, 2008 Many moons ago I had a 250 superdream which if left any longer than a week, needed the carbs draining before it would start. The stuff in the tank seemed to be fine though go figure ? Quote Link to comment Share on other sites More sharing options...
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