Petrol

[dorsetmike]

I have a vague recollection of reading somewhere that petrol deteriorates with age; this has me worried as I last refuelled nearly a year ago. The last time I drove was in March just after its MOT it ran OK then. Anyone able to confirm or deny my suspicion?

[andy]

RAC (and BP) say about six months at 20 degrees.....

www.rac.co.uk/drive/advice/know-how/does-fuel-go-off-old-fuel-and-fuel-storage-questions-answered/

Sell it and get taxis if you don't use it? I guess the tyres will be fairly old too?

[steveandthedogs]

E10 starts to deteriorate after about three weeks, I've been told by two different and reputable sources with no axe to grind - they don't sell the stuff, only mend machinery.

S

[willien]

Does diesel degenerate? While I do a larger mileage than Mike my car often goes for sweeks between trips.

[nickr]

At the end of April, I finished off a can of petrol for my mower that I had had for about 2 years. The mower ran fine.

Why had I had it 2 years? Well I inherited a can of similarly-aged fuel at the time just after I bought it, and I actually bought 2 cans worth then.

However, it certainly does denature with time, and I suspect E10 is rather worse for that than older furmulae.

[peterob]

Jun 7, 2023 14:04:42 GMT dorsetmike said:

I have a vague recollection of reading somewhere that petrol deteriorates with age; this has me worried as I last refuelled nearly a year ago. The last time I drove was in March just after its MOT it ran OK then. Anyone able to confirm or deny my suspicion?

Petrol shouldn't really deteriorate much - it will lose some of the light ends through evaporation if in an unsealed container like a car fuel tank but not a lot.  

Road fuel is not petrol anymore.  It has either 5% or 10% ethanol in it.  This will suffer some evaporative losses as for petrol alone but may also absorb some water.  I very much doubt that you'd notice any difference between March and now.  If you are worried then top up with the dear stuff (5% ethanol) which also has detergents in it although you need to run a couple of tanks of it through to notice a difference,  unless it is a high performance car.

For completeness - Two-stroke fuel does go off.  This is a petrol and oil mix but these days is only used in two stroke engines which are very old technology and certainly not used in cars.  Maybe an old motorbike.  Even lawnmowers and strimmers are four-stroke these days.

[MJB]

Maybe petrochemist can shed some light on the subject. I suspect that you may find some water in fuel and if its been sat so long, then you may have issues with sediment getting sucked up into the pump. Seriously if you haven't used it in a year, then it's time to get rid.

[andy]

FWIW adding a wee drop water to E10 petrol causes the ethanol to separate from the petrol in a matter of hours. It's how folk measure the actual content of ethanol in fuel (it's up to 10% not always 10%) and how folk remove the ethanol so they can run machines that are not compatible with it.

As soon as the fuel is unsealed it will be absorbing moisture out the air and slowly separating.

Diesel goes gummy with time apparently.

[petrochemist]

Thanks for the heads up Martin.

Stability will depend on the formulation, cheap fuels with lots of alkenes will deteriorate much quicker than some of the more expensive fuels. Even the best stuff can loose lighter components so that it doesn't perform so well.
Well sealed samples without alkenes, can sometimes keep quite well - I've tested high grade racing fuel that been stored for over 3 years & showed no change in composition.

Even with deterioration year old fuel should be safe to run, just listen out for knocking & don't work the engine hard. I'd recommend adding some fresh fuel (aim for ~1:1 mix) and use higher octane fuel (or better still add an octane booster) for this if the engine is pinking/knocking at all.

The hydrocarbon portion of diesel should stay stable for centuries, but today's fuel has biodiesel added and this can degrade much quicker, giving rise to the gumminess andy referred to.

[andy]

Jun 7, 2023 16:29:44 GMT peterob said:

Jun 7, 2023 14:04:42 GMT dorsetmike said:

I have a vague recollection of reading somewhere that petrol deteriorates with age; this has me worried as I last refuelled nearly a year ago. The last time I drove was in March just after its MOT it ran OK then. Anyone able to confirm or deny my suspicion?

Petrol shouldn't really deteriorate much - it will lose some of the light ends through evaporation if in an unsealed container like a car fuel tank but not a lot.  

Road fuel is not petrol anymore.  It has either 5% or 10% ethanol in it.  This will suffer some evaporative losses as for petrol alone but may also absorb some water.  I very much doubt that you'd notice any difference between March and now.  If you are worried then top up with the dear stuff (5% ethanol) which also has detergents in it although you need to run a couple of tanks of it through to notice a difference,  unless it is a high performance car.

For completeness - Two-stroke fuel does go off.  This is a petrol and oil mix but these days is only used in two stroke engines which are very old technology and certainly not used in cars.  Maybe an old motorbike.  Even lawnmowers and strimmers are four-stroke these days.

The only fuel I had for long enough to go off was 2 stroke nitromethene for a RC car. It took many years though.

[Deleted]

Jun 7, 2023 16:29:44 GMT peterob said:

Jun 7, 2023 14:04:42 GMT dorsetmike said:

I have a vague recollection of reading somewhere that petrol deteriorates with age; this has me worried as I last refuelled nearly a year ago. The last time I drove was in March just after its MOT it ran OK then. Anyone able to confirm or deny my suspicion?

Petrol shouldn't really deteriorate much - it will lose some of the light ends through evaporation if in an unsealed container like a car fuel tank but not a lot.  

Road fuel is not petrol anymore.  It has either 5% or 10% ethanol in it.  This will suffer some evaporative losses as for petrol alone but may also absorb some water.  I very much doubt that you'd notice any difference between March and now.  If you are worried then top up with the dear stuff (5% ethanol) which also has detergents in it although you need to run a couple of tanks of it through to notice a difference,  unless it is a high performance car.

For completeness - Two-stroke fuel does go off.  This is a petrol and oil mix but these days is only used in two stroke engines which are very old technology and certainly not used in cars.  Maybe an old motorbike.  Even lawnmowers and strimmers are four-stroke these days.

My strimmer which is relatively new uses 2 stroke. I use the recommended Apsen 2. Works fine.

[Chester PB]

Since Covid lockdown, my wife and I have only been putting unleaded in the car every 2 or 3 months, with no apparent problems.

However, I have found that tyres can 'perish' and began to break up after only a few thousand miles if they are 4 or 5 years old. Within the last year I have had to replace 4 for this reason, and all had plenty of depth left on the tread. Before I retired I always had to replace tyres because the tread was worn close to legal limits, but now they perish long before that because of the low mileage the car does (only about 1,000 miles last year).

[John Farrell]

Jun 7, 2023 20:54:32 GMT Chester PB said:

Since Covid lockdown, my wife and I have only been putting unleaded in the car every 2 or 3 months, with no apparent problems.

However, I have found that tyres can 'perish' and began to break up after only a few thousand miles if they are 4 or 5 years old. Within the last year I have had to replace 4 for this reason, and all had plenty of depth left on the tread. Before I retired I always had to replace tyres because the tread was worn close to legal limits, but now they perish long before that because of the low mileage the car does (only about 1,000 miles last year).

I had to replace all four tyres at my car's last service - the sidewalls were badly cracked (the mechanic showed me). The tyres were date coded 2015, but still had legal tread depth.

[mick]

Jun 7, 2023 22:00:51 GMT John Farrell said:

Jun 7, 2023 20:54:32 GMT Chester PB said:

Since Covid lockdown, my wife and I have only been putting unleaded in the car every 2 or 3 months, with no apparent problems.

However, I have found that tyres can 'perish' and began to break up after only a few thousand miles if they are 4 or 5 years old. Within the last year I have had to replace 4 for this reason, and all had plenty of depth left on the tread. Before I retired I always had to replace tyres because the tread was worn close to legal limits, but now they perish long before that because of the low mileage the car does (only about 1,000 miles last year).

I had to replace all four tyres at my car's last service - the sidewalls were badly cracked (the mechanic showed me). The tyres were date coded 2015, but still had legal tread depth.

Same here. In fact on the fronts the tread was starting to separate from the rest of the tyre (Michelin Pilots). I've never experienced that before.

Mick

[peterob]

Jun 8, 2023 6:18:45 GMT mick said:

Jun 7, 2023 22:00:51 GMT John Farrell said:

I had to replace all four tyres at my car's last service - the sidewalls were badly cracked (the mechanic showed me). The tyres were date coded 2015, but still had legal tread depth.

Same here. In fact on the fronts the tread was starting to separate from the rest of the tyre (Michelin Pilots). I've never experienced that before.

Mick

These posts remind me to check the tyres again.  They lose pressure "more" if the car is standing and it is important to rotate the wheel from time to time so that new tyre is in contact with the ground. if not they don't stay round.  I suspect that the composition of tyres has changed over the years to reduce losses of volatile hydrocarbons and less plasticiser means more tendency to crack. Exposure to direct sunlight won't help, neither will exposure to ozone in the air, average concentrations of which have been going up.