Petrol degradation

[TarmacTerrorist]

Just wondering out of interest really about the life span of petrol. We've all heard of petrol 'going off' before, but how long does it take to go off and what is it that actually causes it to go off?

I've heard stories that Shell Optimax unlike BP Ultimate is enriched with additives to give it it's higher octane rating, which over a very short period of time degenerate rendering it as good as old 95?

If this is true then what sort of quality could you expect from a garage with slower moving sales who are waiting to have their tanks filled and are dishing out the dregs??

Comments appreciated.

Vinny

[PhilT]

Not sure about the timescales, but I always fill up at Shell stations that have a heavy flow of cars, i.e. motorway or main road.

[johneroberts]

Shell make it very hard for the "not so busy stations" to sell optimax, we had to wait for 18months until we go optimax in our town, before that it was a 24ml round trip to the nearest one. So the event of petrol going off i think is pretty small, in the case of a station that has been given optimax to sell.
Cheers
jr

[scillyisles]

Shell make it very hard for the "not so busy stations" to sell optimax, we had to wait for 18months until we go optimax in our town, before that it was a 24ml round trip to the nearest one. So the event of petrol going off i think is pretty small, in the case of a station that has been given optimax to sell.
Cheers
jr

This is correct - All Shell Optimax is produced at the Stanlow refinery in Cheshire and as such Shell have logistical problems ensuring distribution across the country. Therefore before a garage can sell Optimax, Shell make sure that there is demand for the fuel in the area -AFAIK the garage also has to have underground storage tanks to a higher spec in order to sell Optimax.

[DavidT]

I didn't realise it was so complex.

I am going to look at the dates on the boxes of millers I have now

[peterb]

I've heard stories that Shell Optimax unlike BP Ultimate is enriched with additives to give it it's higher octane rating, which over a very short period of time degenerate rendering it as good as old 95?

Ooo-err. So, it's probably not a good idea for me to keep the tank full (82 litres) of Optimax if the car's not going to be used for 3-4 weeks?

[scillyisles]

Shell don't recommend that you "store optimax in a tightly sealed container for more than six months" I'm not sure that in a car fuel tank could be truly defined as a tightly sealed container so I would have thought less time in a car tank.

The main benefit from Shell Optimax is not the RON number, in fact all the tests that Shell did claiming better performance were by comparison with normal (95 RON) unleaded, but are the "cleaning properties" of the fuel which is supposed to remove deposits in the engine etc to make it more responsive.
Typically, these deposits are found in older less efficient engines and it's in these cases that Optimax has shown better performance/responsiveness. The benefits of running Optimax in clean modern efficient engines are less proven and some could argue not really worth the extra Optimax cost. So a more sensible/cost effective approach would be to only use Optimax every so often for it's cleaning properties (say a tankful every month) and use SUL for the rest of the time.

[peterb]

So a more sensible/cost effective approach would be to only use Optimax every so often for it's cleaning properties (say a tankful every month) and use SUL for the rest of the time.

The first three times I filled my car with Esso SUL. From then (~1000 miles) on I've used Optimax. From my first tank of Optimax it showed an immediate improvement of 2mpg over the Esso SUL. This may have something to do with the engine loosening up, but the effect was very marked from the very first tank full.

One day I might get caught short whilst out of reach of a Shell, in which case I'll then find out what mpg I get from SUL.