Am i right in saying that my tank full of optimax would have less of an octane rating the longer its in the tank? The reason i ask is that my car is away getting some work done on it and when its finished its going on the rolling road. The car has been gone for nearly 9 weeks now and had half a tank left when i dropped it off and its probly going to be another few weeks till its going on the rolling road. So if the fuel has been in the tank for say 11 weeks would that affect its performance? Thanks.

 

Yes. I'd use it for early/midrange mapping.

 

 

yep definately go's off over time. won't even run after a couple of years in the tank.

 

The fuel in the tank of my cosworth has been there 6 months At least there isn't much left in there now.

 

id drain it and use it for a different car, thats what i do as my mondeo runabout doesnt care what it runs on.

 

why the face? optimax is different to other fuels, its octane comes from additives that can go off

 

fuel in the system does go off over time, weeks won't make as much difference as years though, but when yuo have lots of coughing and spluttering it does make sense to give it a fresh tank full after a while to amke sure it's all up to scratch

i wonder which mag will do a feature on this?

 

retro ford did one early last year iirc, not much good for this thread as they tested the effects on a tuned carb'd x-flow though, granted thats 100% different to an injection system but there was still 11hp in the difference

 

yeah it goes off over time, although i'm not sure how much a few weeks will make

to be honest i wouldnt risk it just in case, for the sake of a tank of fuel, just put fresh in for a mapping session

 

If it's optimax I expect it's as potent as water after all these years.

 

i lobbed the old petrol out of me gararge in me mower, it started after i'd cleaned the spark plug, but it coughed and choaked whilst i used it. mabey it'll run better of fresh fuel?

 

Yes fuel goes off surprisingly quickly if not stored in an airtight container.

If its in fuel cans though, it doesnt seem to degrade the same

(ive noticed pinking on old fuel left in tank, but not from old fuel in full cans)

 

Depends on how you look at it, if he is likely to leave fuel that long in future and then drive the car on it, its probably best it is mapped for doing so.

If its mapped on the ragged edge with fresh fuel then run on old fuel, it could easily melt as a result.

My rule is always to map on the worst fuel the car will be running, so if its old fuel that will be the it runs, then map on that!

 

As said above, Optimax/V Power holds it's octane rating for the least amount of time compared to other high octane pump fuels.

 

good point

i did used to drive my cossie, it wouldnt have long enough to go off!

 

So tesco 99 will be fine after a couple months in fuel tank??

 

id just top it up to the brim with new stuff