It has been mentioned on this thread that the octane value of fuel reduces with time, which indicates to me that there is some sort of shelf life.

Is this due to fuel bio-degrading, or fuel additives going out of suspension?

The reason I ask is that my 4 will sometimes sit for quite a period of time unused with a full tank of fuel. When I get the chance to drive it, I don't want any suprises caused by a degradation in the fuel in the tank.

Graham

What sort of timescale are we taking about here?

If it's a week or two then I wouldn't worry toomuch.

If it's months then you might want to think about making sure the tank is low whenever you leave it so you can top up fresh on your way out.

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JDM ST205 (286bhp and 281lb/ft)
JDM ST202 (Finally sold )
1982 Pontiac Trans Am 5.7L V8 (See my website)

Normally 2 to 3 weeks, but last year I was away for 4 months.

Graham

The parts of the fuel that give the higher RON rating are much lighter than the rest of the fuel and more likely to evaporate off over time, hense the RON reducing. I don't know the full technicalities but my old man worked for Esso for nearly 30 years so I believe him *lol*.

I've been running Tesco 99 for a while and not seen any obvious problems and performance was acceptable. However, the other day I was caught short and no Tesco nearby so I had to fil lup with Optimax. I wasn't really expecting a difference but I think I did find the Optimax to be a little better. As said before, it just sounded better and felt a little smoother. Think I might go back to it for good.

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'92 GT-Four RC - Project Rufus - something of a mover.
'05 Audi A3 3.2 V6 Quattro S Line - not bad for a daily.