Skylarking
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Hm, don’t know but isn’t 98RON a more refined fuel grade which contains more volatile components as compared to 91RON? I‘m not a chemical engineer working in the petrochemical industry so can’t say, but if that’s so, it seems logical to accept how the more refined volatile compounds would be the first to evaporate, since they are more volatile. As such, I‘d think 98 would have a shorter shelf life than say 91. And just like radioactive decay, wouldn’t that mean if 98 looses its aromatics or other volatile compounds, then what’s left behind may be something that is more akin to 91?Since this is a fuelly thread ... I had the old project car pink-slipped today, was talking to my mechanic about the stuck IAC, and he initially thought the problem might be fuel.
He said 98 is really unstable & only lasts a month before getting dodgy ... he reckons 95 is nowhere near as unstable, and that if you go for a drive before the car's going to be parked for some time you should try & use as much as possible of your 98 & put at least a half-tank of 95 in for when it's sitting there. He also reckons never use 98 for mowers, whippersnippers etc for the same reason.
Whatever the case, old fuel ain’t as good as new fuel. However, I must also confess I haven’t had issues with either 98 or 91 in my lawnmowers (I have two, a 2 stroke and a 4 stroke). I just use whatever is convenient on the day I fill up the 5ltr can and it lasts me many months