Shell V-Power "going off" ?

[wolfsbaneracing]

Is Shell V-Power (99 ron) known for 'going off' ? (ie losing its anti-knock properties)

My 'fun' car is a '61 Healey 3000. Triple carbs, fast-road cam, 6-branch exhaust, timing tweaked to suit highest octane fuel I can find.
I've owned the car since 1991; I know it and all its foibles intimately.

Since moving house about 2 years ago I have run the car exclusively on Shell V-power (the garage is at the end of my village).
All fine and dandy until today. Jumped in to drive to a local air-ambulance / classic car meet and had to return to base ...

The car was last driven (reasonably hard) in mid-February (ie 3 months ago) and still had just under 1/2 a tank of fuel left.
This afternoon it was running rough, excessive popping and banging, would barely tick-over and was pinking like hell on a whiff of throttle in 3rd gear !
The car has never before behaved like this. A quick stop and timing retard did effectively nothing to improve the situation.

So, back to the village and some new fuel. Half a tank added (of the usual V-power) had it brim full. Timing adjusted back to its normal setting.
Within a few hundred metres it was running as normal again !
Out of the speed-limited area it pulled through 2nd, 3rd and 4th on full bore with no pinking whatsoever - back to its usual boisterous self.

There is no explanation for this other than the fuel.
Anyone else had a similar experience ? And what thoughts to deal with the issue ??

[Spudgunassassin]

It doesn’t take long for petrol to go off

[wc98]

It definitely goes "off". Various things i have read state anywhere from 3 to 9 months for petrol, though it appears to depend on storage conditions.

[trashbat]

When was it last filled up?

[wolfsbaneracing]

I'm aware that fuel does go off. But I have never had the issue before today (or certainly not to such an extreme degree).
I previously ran the car on predominantly BP 'Ultimate' 98, hence wondering if Shell V-Power is more susceptible ??

[wolfsbaneracing]

trashbat said:

When was it last filled up?

Mid-February, 3 months ago.

[trashbat]

It's not long enough IMO, unless the supplied fuel was already bad. But it depends: how much did you put in at that point? Because obviously you're always left with some diminishing percentage of older fuel from the last fills.

[Lincsls1]

I believe E10 fuel to go off, but premium E5? Not so sure. Even so I'd have thought a minimum of 6 months.
My Monaro was left in the garage and on SORN from November 1st and not run once until May. It started and drove perfectly fine, didn't feel like it was down on power or do anything untoward.
Very similar story with the lawn mower too. I run that on the same fuel. Sits in the shed all winter, started and ran perfectly with the fuel still in the tank, always does, every year.

[E63eeeeee...]

It seems very unlikely to me that it goes off in 3 months in a fuel tank. I've regularly had cars not started for several months usually on V power and had no problems at all. Anyone who has a car that only does a few hundred miles a year is very likely driving it on year-old fuel sometimes. A couple of weeks ago I started one that had been parked up for something like 3 years, also on V Power, also ran fine. I'll run that one dry and change the fuel filter just in case, but having read this kind of thread before I was expecting it to be a very different experience.

[Panamax]

What happens to petrol left standing is that the lighter fractions evaporate off. How quickly that happens depends on temperature and the amount of ventilation. This is why you hear people thrashing about trying to start garden machinery each spring. Get some fresh fuel in there and all will be fine. Store your garden equipment empty.

In a car petrol tank you need to consider the volume of fuel in there, the exposed surface area of the fuel and the amount of air movement. In other words, you're more likely to have trouble if the tank was low on fuel when the car was stored.

Modern cars have a truly thumping high tension spark and are generally much easier to start. They also adjust timing automatically for fuel quality.

[trashbat]

You would still be on half bad fuel now too, so generally you would expect a severe problem to be only mitigated, not solved.

[Riley Blue]

My Riley goes into hibernation at the end of each October to re-emerge March/April, has done for the last 12 years and it's never had a problem with 'gone off fuel'.

It's run on Tesco 99RON Momentum 95% of the time and does around 4,000 miles a year.

[wolfsbaneracing]

trashbat said:

You would still be on half bad fuel now too, so generally you would expect a severe problem to be only mitigated, not solved.

Agreed ! But I went from a chalk to a cheese situation just by adding half a tank.
It doesn't add up in my head, but the sequence of events is factual history. Hence my post, wondering if V-Power is particularly finicky fuel ...

[Heaveho]

In my quite long term experience of storing cars, and independent tests that seem to confirm those experiences, Shell V Power is more likely than any other fuel to resist deterioration.

I've stored my Mk1 MR2, a car known for having fuel pump issues in these circumstances, and it simply started and ran after 3 years with zero issues. It was stored on Shell V power.

The tests I saw compared several manufacturers premium fuels, Shell, Tesco and Esso being those of note. When tested, at point of purchase, the V Power had a RON of 102, and was still at 99 after 2 years in storage. Tesco was a close second, Esso, surprisingly, noticeably worse. I've never had a fuel related issue from storing cars over a 20 year period on Shell, the cars being my Evo, Boxster and the already mentioned MR2. All of them have had to sit for between 2 and 3 years in the time I've owned them.

[av185]

Run a selection of Porsche GTs over the years all sorned over winter (dry garage) up to 6 months in some cases all run on Shell jungle juice most low fuel never had an issue.

[2172cc]

I had to dispose of 3/4 of a tank of V Power when my car just wouldn't run properly after about 6 months of not being used. We checked everything and all appeared ok so only thing left was the fuel. Drained the tank and put in 15 litres of Tesco 99 and it fired straight up and ran perfectly. Previously only ever used Shell V Power but now run all the time on Tesco 99.

[wolfsbaneracing]

@2172cc

May I ask what your car in question is, what state of tune ?
Is it more akin to my situation; no electronic anything, but a fast-road carbs and points engine ?

I'm wondering if a car with an ignition management system (eg an Evo) simply deals with the issue automatically ...

[2172cc]

wolfsbaneracing said:

@2172cc

May I ask what your car in question is, what state of tune ?
Is it more akin to my situation; no electronic anything, but a fast-road carbs and points engine ?

I'm wondering if a car with an ignition management system (eg an Evo) simply deals with the issue automatically ...

It's a Sunbeam Lotus. Engine has been rebuilt to a fast road spec, has MSD. electronic ignition, twin 45 Carburetors and Facet electric fuel pump. When the issue started, I'd just got to the end of my road then lots of blue smoke from the exhaust and running really rough and lumpy. It had only covered about 1500 miles after a full ( and expensive) rebuild. Not had the issue reoccur since.

[Tango13]

I run my 370Z almost exclusively on V-Power from the same filling station and every once in a while my mpg will take a dive as if the stock in the main tank has gone off.

Also seems to happen just before fuel prices drop, like they're not putting the expensive additives in?

[evil.edna]

The anti-knock constituents are volatile aromatics. The recent warm weather will have helped liberate some of them from your tank.

This particular phenomenon became an issue for all manufacturers of downsized turbocharged engines during the first lockdown.