Effects of ageing fuel on octane rating and motor

[aaronng]

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

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?

[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.