Effects of ageing fuel on octane rating and motor

[Phantom Snail]

Hi guys,
i have a question in regards to fuel.
Ive filled up a full tank of BP Ultimate towards the end of october last year...there was just over 3/4 of a tank according to the fuel gauge before i put it into storage for a trip and i just got back...so now the fuel is abit over 3 months old...
I was thinking that most likely the octane rating has dropped...
1 - would this be a correct assumption?
2 - so being a lower rating of octane, it cant be too good for the motor?
3 - what should i do about it? I was thinking about siphoning it out, but thats over 30 litres of fuel.. which is too much.. i was also thinking about putting abit of octane booster n some injector cleaner into the tank - but ive heard that octane boosters would do even more damage n harm to the motor.. and i dont want to drive it even granny style until the fuel is gone because im afraid it would do damage to the engine...

Any help is greatly appreciated...

Cheers

[aaronng]

You might as well top it up with more Ultimate (or whatever 98 octane that you like). That's better than octane booster for sure.

[silver_screen]

if its been a tad over 3 months.. the octane rating wouldnt have dropped by much at all...

Instead of being 98 its probably around 97ish.. it takes more than a 3 months to kill fuel :)

Ive had fuel in my rx7 for about 7 months now :) and its still ok... sort of..

[silver_screen]

oh and btw... what kind of motor is it???

If its just a street car.. your engine will be perfect no matter what the condition of the fuel might be (unless its been watered down.. or over 10months)

[Phantom Snail]

You might as well top it up with more Ultimate (or whatever 98 octane that you like). That's better than octane booster for sure.

Mmm but like 5-10 litres of bp ultimate wont really make much of an effect on 35 litres of "stale" fuel would it? so then thatd be like 35 litres or so of "stale" fuel mixed with about 5-10 litres of new fuel.. still bad for the engine overall isnt it?


oh and btw... what kind of motor is it???

If its just a street car.. your engine will be perfect no matter what the condition of the fuel might be (unless its been watered down.. or over 10months)

Its a b18c7 with a few mods...no aftermarket ecu tho...just apexi neo..

[silver_screen]

Then it'll be fine.. they dont need a diet of extreme fuels :)

Even my heavily modifed rx7 live without the good stuff for a short while :)

[EuroAccord13]

Fill up the tank.. Drive it and empty the tank and you'll be fine...

Fuel goes off in like 2 weeks...

[string]

Fuel goes off in like 2 weeks...
Yet it still runs my engine after 6 months... amazing! I must have filled with BP Magical instead of Ultimate last time.

Some evidence for your claim please?

[aaronng]

Yet it still runs my engine after 6 months... amazing! I must have filled with BP Magical instead of Ultimate last time.

Some evidence for your claim please?

Goes off, but still usable. LOL, you need to learn not to take things literally. I drink milk that goes off. Yummm.

[EuroDude]

I had fuel in my civic for like 6 months, no probs with the fuel at all.

Although I did use 95RON in a 92RON tuned engine ;)

[yfin]

Provided fuel is stored in a relatively sealed environment it will last a minimum of 6 months. In 3 months the RON in your fuel has hardly changed enough to be worried about.

[string]

Goes off, but still usable. LOL, you need to learn not to take things literally. I drink milk that goes off. Yummm.
If it's still usable, what "goes off"? :confused:

[aaronng]

If it's still usable, what "goes off"? :confused:

The more volatile fractions. Petrol does not consist of only 1 component. It's a blend. The light fractions that are easier to burn tend to evaporate and will escape. So in the end, you get a fuel that still burns when the spark plug fires, but doesn't give out as much energy as "fresh" fuel.

[silver_screen]

fuel does not go off in 2 weeks

it takes 6 months for the octane rating to drop which even then is extremely minimal.... fuel tanks r a very well sealed enviroment.. it'll be fine

[string]

fuel does not go off in 2 weeks

it takes 6 months for the octane rating to drop which even then is extremely minimal.... fuel tanks r a very well sealed enviroment.. it'll be fine

Exactally what I was thinking. The whole contents of the tank can evaporate for all it intents and purposes, it's a closed system.

[muhhan]

Today I'm sure I heard a 'tink', 'tink', 'tink' sound coming from my engine. I've never had someone tell me this is what pinging sounds like but I suspect it may be pinging. The sound I heard today could be best described as a hammer very lightly tapping a piece of metal. It was reasonably regular maybe once every 2 seconds. I did have to concentrate and focus on the sound to hear it among the other engine noises (I like listening to the sound of engines).

Reason why I'm posting in this thread is that if my engine was pinging I can't explain why except for the fact that the fuel in my car has been in there for about 18 months (possibly more) and the octane rating has dropped enough to cause the engine to ping. It is 7/8th full. It was filled with regular unleaded at the time.

What do others think?

[aaronng]

If it was filled with regular 91, and your engine requires 91 to run, then after 18 months, it might have dropped to 90 or even 89.5, which is at the borderline for your engine. Why don't you try topping up with 98 octane for that last 1/8th of the tank and see if it stops the tinking sound?

[muhhan]

Thanks. I will try that. I might see if I can siphon some out to make room for more good quality fuel. Could always use the old stuff for the lawn mower.

And if the question hadn't crossed your mind, the car isn't registered that is why the fuel has been sitting in there for so long, hence filling up will be a bit of a task. Might have to do the milk run to get it loaded.

[aaronng]

Thanks. I will try that. I might see if I can siphon some out to make room for more good quality fuel. Could always use the old stuff for the lawn mower.

And if the question hadn't crossed your mind, the car isn't registered that is why the fuel has been sitting in there for so long, hence filling up will be a bit of a task. Might have to do the milk run to get it loaded.

If it has been sitting for that long, then it might not be your fuel, but the engine being corroded due to the lack of oil in the internals after being left for that long. Change your engine oil and all yoru fluids too.

[muhhan]

Oil, oil filter and other fluids still get changed regularly as per service schedule (for time elapsed) and the car is started at least once a week for around 10 minutes, normally driven forward and backward in the driveway for a couple of metres. The car was running fine without the noticeable 'tink, tink' noise last week it was only this week (on the week end just past) that I heard this noise, which lead me to the aging fuel as a possible cause.

[aaronng]

Oil, oil filter and other fluids still get changed regularly as per service schedule (for time elapsed) and the car is started at least once a week for around 10 minutes, normally driven forward and backward in the driveway for a couple of metres.

You added 98 octane yet?
BTW, how do you drive for 10 minutes on a driveway? :p

[VT3C]

i dont think will be any problem - considering those of us running jdm engines which are tuned for 100RON are using 98 with no serious effects (so far hahah).. but in extreme cases you could always retard ignition timing slightly to reduce chance of detonation.