ADUK Archive

How long does it take for fuel in a car fuel tank to stagnate / weaken?

I use 99 Octane fuel and sometimes the car is left in a the garage for a few days and not used. I wondered what length of time or inactivity would be needed to render the fuel not as potent, and perhaps lack some performance when used again...

I've heard 3 months.





There's your excuse, now go on go for a drive

It's a lot less time than three months, try a month, two months, in a sealed container, (A "stabilizer" should be added after that) for it to become "stale", it'll still burn etc, but it's the easily ignitable Hydrocarbons, and additives in it that flash off first.

James wrote:How long does it take for fuel in a car fuel tank to stagnate / weaken?

I use 99 Octane fuel and sometimes the car is left in a the garage for a few days and not used. I wondered what length of time or inactivity would be needed to render the fuel not as potent, and perhaps lack some performance when used again...

I wouldn't worry about it, I'm sure you've more than enough performance anyhow - and I expect the car goes quite well too.

You young tearaways seem fixated with performance; there's more to life than speed y'know.

I expect the Stressed One will now be along PDQ to give me another bollocking for referring to tearaways.

Best wishes all,
Dave.

LOL

I just want to know whether filling up 10 days prior to using the car costs me anything in terms of performance - the car has a really weird ECU that detects the exact petrol make up and adjusts the vehicles performance accordingly. If I change fuel type to a lower Octane I have around 1 - 2 tanks of "limp home mode" performance whereas if I move from a low Octane up to a higher one it takes around 1 tank for the ECU to exploit all the available RON.

I've yet to drive any car that goes into limp home mode just because it's had normal unleaded put it in. I would perhaps expect something like that on a 500bhp custom build turbo engine (Skyline/Cosworth maybe) but not on an OEM car.

In my car (non-turbo but 100bhp /litre) I can't really tell what fuel's been put in but I tend to use Optimax anyway. On my motorbike I reckon I can tell when it's got 98 octane in but that's probably psychological as I know what's just been put in it.

It isn't a drastic limp home mode, but the difference is enough to tell qute easily. I think it shortens the boost slightly and takes away some response. All I know is when I do change fuels (which I dont tend to do now) the car's character changes completely making for a very unfulfilling drive.

hardboiled wrote:I've yet to drive any car that goes into limp home mode just because it's had normal unleaded put it in. I would perhaps expect something like that on a 500bhp custom build turbo engine (Skyline/Cosworth maybe) but not on an OEM car.

In my car (non-turbo but 100bhp /litre) I can't really tell what fuel's been put in but I tend to use Optimax anyway. On my motorbike I reckon I can tell when it's got 98 octane in but that's probably psychological as I know what's just been put in it.

Gotta agree with this. it won't be in limp home, the Engine Management light on the dash would be on if it was. what will be happening is the knock sensor/s will be sensing detonation and The managment system will be altering the rest of the settings to suit.

Bikes and fuel, if I use Shell V-power in the bike I notice a difference in the fuel consumption.....it gets better, which suggests to me it's running more efficiently

I could tell the difference in fuels on the bike in terms of mpg and ummphh so stuck to optimax type fuels.

The only car I've ever known to show a preferance to fuels was my Alfa 75 2.0TS, mind you James, it was a proper car, RWD, De Dion rear axle and rear gearbox, plus from an era when 150bhp was proper performance, not like now when you have 8,000,000 bhp to get to 60 mph 1.5 seconds faster and 50,000,000 computers to control getting that power down!!!

Also it was an Alfa, so it got lighter every mile as bit's fell of it!!!

kwakba wrote:The only car I've ever known to show a preferance to fuels was my Alfa 75 2.0TS

How much difference did you observe? When we had 2.0's I don't think we could detect any significant difference despite driving them enthusiastically. With our 3.0 there appears to be a slight improvement in performance with higher octane petrol, but we fill with standard most of the time, mainly using the more expensive when we know our friends are likely to be driving it.

Double blind test. The power of marketing is strong in this young Jedi.

7db wrote:Double blind test. The power of marketing is strong in this young Jedi.

That sounds like a polite way of recognising that we now live in a world with more than its fair share of bullsh1t.

It's all getting very difficult; you need wellies and a big shovel everywhere you go these days.

Best wishes all,
Dave.

Gareth wrote:

kwakba wrote:The only car I've ever known to show a preferance to fuels was my Alfa 75 2.0TS

How much difference did you observe? When we had 2.0's I don't think we could detect any significant difference despite driving them enthusiastically. With our 3.0 there appears to be a slight improvement in performance with higher octane petrol, but we fill with standard most of the time, mainly using the more expensive when we know our friends are likely to be driving it.

It was smoother and would do another 80miles on a tank of fuel - wasn't as if it was faster, just noticebly smoother esp when the variable cam kicked in.