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14 hours ago, Peter M said:

Variation: Just drive it and use full throttle once the engine comes up to temperature.

I think pulling fuses is just BS. 

 

That BP factsheet was interesting:

As the volatiles evaporate fuel gains about 1 RON in octane and about 40g in density per litre after being stored in a equipment fuel tank for 5 weeks.  Never seen actual metrics like this before.

What I hadn't thought about is this effectively makes the engine run richer with a change from 13:1 to 12.3:1 over the same period.  I guess that could further compound the cold start issue that is made more difficult by the loss of volatiles.  

My view with fuel is, if the engine will start cold, just drive it.  If it's hard to start, only top up with fresh fuel then.  If it is a motorcycle or lawnmower, pushing into the sun to warm up often does the trick.

 

That's fair. I'll see how it starts up when I take it out this week. As a rough guide and based on your experience @Peter Mhow long do you think 98 will be safe to use in your fuel tank from the initial pouring? 

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I posted up earlier in this thread - mine had regrettably sat for several months, and I fear the petrol in it was over six months old. Maybe even a year... (eeeek) I moved it from my yard to a temporary garage an hour away. I was worried I'd have issues driving it, but it fired up and ran like a top on the freeway. Not so much as a hiccup. Then I filled the tank and put fuel stabilizer in it. It was all I could do unfortunately. It does have a new fuel filter in, so hopefully that would catch any muck.

I've been meaning to send out the injectors to get cleaned. I doubt it's ever been done. Or maybe just get new ones.

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13 hours ago, Peter M said:

Why? I'm curious about your reasoning.

The octane rating of the fuel decreases over time.  I've usually had turbocharged cars or high strung N/A motors, driving it easy until a fuel tank of fresh fuel is much cheaper than dealing with the possibility of detonation.  But I'm conservative, its also why I've always slurped 20 litres of 109 in any turbocharged car I take to the race track 

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11 hours ago, rminc said:

That's fair. I'll see how it starts up when I take it out this week. As a rough guide and based on your experience @Peter Mhow long do you think 98 will be safe to use in your fuel tank from the initial pouring? 

rminc,

I don't think there is an answer to that one as it depends on so many things.  My 911 seems insensitive to fuel age but my Ducati will barely start and run with 18 month old 98 in its tank.  My Honda lawnmower needs to pre-warmed in the sun once its 95 gets to about 6 months old.  My wife's Honda car gives the impression it would start and run on anything with barely a miss!

Not that I deliberately try to run my engines on old fuel mind you, its just my observations over time, particularly over the last couple of years where I've moved 400km and had to store some vehicles while this happen.

Providing I'm confident that the fuel tank has been protected from water contamination, I would just try the fuel as is as I don't think there is any risk.  If it starts and runs poorly only then would I either top up or flush and replace the fuel then. 

 

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10 hours ago, 1q2w3e4r said:

The octane rating of the fuel decreases over time.  I've usually had turbocharged cars or high strung N/A motors, driving it easy until a fuel tank of fresh fuel is much cheaper than dealing with the possibility of detonation.  But I'm conservative, its also why I've always slurped 20 litres of 109 in any turbocharged car I take to the race track 

Race fuel?  I'm out my depth here and the advice available always seems to be well coated in caveats like: Octane Stability: High Octane vs Low Octane Fuels - Sunoco Race Fuels

For the pump fuel wangan likely has in his 3.2 tank, the BP factsheet shows the fuel octane actually increasing and mixture effectively "enriching" making detonation less likely. 

 

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On 20/09/2021 at 18:46, Peter M said:

rminc,

I don't think there is an answer to that one as it depends on so many things.  My 911 seems insensitive to fuel age but my Ducati will barely start and run with 18 month old 98 in its tank.  My Honda lawnmower needs to pre-warmed in the sun once its 95 gets to about 6 months old.  My wife's Honda car gives the impression it would start and run on anything with barely a miss!

Not that I deliberately try to run my engines on old fuel mind you, its just my observations over time, particularly over the last couple of years where I've moved 400km and had to store some vehicles while this happen.

Providing I'm confident that the fuel tank has been protected from water contamination, I would just try the fuel as is as I don't think there is any risk.  If it starts and runs poorly only then would I either top up or flush and replace the fuel then. 

 

Thanks @Peter M How would you be able to assess if it was protected from water? 

With the nice weather in Melbourne today I went for a decent 1 hour drive. The car started first crank after 2 months on the trickle charger, but did sound a touch lumpy as I was warming it up. Would you think this is due to the fuel? 

 

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4 hours ago, wangan said:

Thanks @Peter M How would you be able to assess if it was protected from water? 

With the nice weather in Melbourne today I went for a decent 1 hour drive. The car started first crank after 2 months on the trickle charger, but did sound a touch lumpy as I was warming it up. Would you think this is due to the fuel? 

wangan,

If you find a fuel tank or fuel drum left in the open with water ponded around the cap, be suspicious. A car without a petrol cap or just a rag shoved in the filler, be suspicious.  However I'm pretty confident you're car doesn't fall in this category and only mentioned this risk to offer up a full answer.

I think your car is fine and the lumpy idle was due to the engine simply being cold and running on cold start enrichment where combustion isn't always perfect.  If it suffered from contaminated fuel it would run poorly all the time.

I often respond to posts because people overthink things.  Combine that with some other's posting old wives tales and that's a recipe for unfounded anxiety which I don't like to see others suffer.

More time driving and less time on forums is the universal cure!

 

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30 minutes ago, Peter M said:

wangan,

If you find a fuel tank or fuel drum left in the open with water ponded around the cap, be suspicious. A car without a petrol cap or just a rag shoved in the filler, be suspicious.  However I'm pretty confident you're car doesn't fall in this category and only mentioned this risk to offer up a full answer.

I think your car is fine and the lumpy idle was due to the engine simply being cold and running on cold start enrichment where combustion isn't always perfect.  If it suffered from contaminated fuel it would run poorly all the time.

I often respond to posts because people overthink things.  Combine that with some other's posting old wives tales and that's a recipe for unfounded anxiety which I don't like to see others suffer.

More time driving and less time on forums is the universal cure!

 

Well said. 

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On 23/09/2021 at 19:22, Peter M said:

wangan,

If you find a fuel tank or fuel drum left in the open with water ponded around the cap, be suspicious. A car without a petrol cap or just a rag shoved in the filler, be suspicious.  However I'm pretty confident you're car doesn't fall in this category and only mentioned this risk to offer up a full answer.

I think your car is fine and the lumpy idle was due to the engine simply being cold and running on cold start enrichment where combustion isn't always perfect.  If it suffered from contaminated fuel it would run poorly all the time.

I often respond to posts because people overthink things.  Combine that with some other's posting old wives tales and that's a recipe for unfounded anxiety which I don't like to see others suffer.

More time driving and less time on forums is the universal cure!

 

I rememeber reading 10 weeks before it starts to solidify in your lines (areas where the fuel is in small volumes).

I also have been 95 RON has a better shelf life for both performance and storage, providing your comp isn't too high. 

What fuel do you use @Peter M

On 20/09/2021 at 19:01, Peter M said:

Race fuel?  I'm out my depth here and the advice available always seems to be well coated in caveats like: Octane Stability: High Octane vs Low Octane Fuels - Sunoco Race Fuels

For the pump fuel wangan likely has in his 3.2 tank, the BP factsheet shows the fuel octane actually increasing and mixture effectively "enriching" making detonation less likely. 

 

As far as I know fuel octane and detonation resistance aren't directly corrolated. You can have lower octane fuel which doesn't detonate either. 

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5 hours ago, rminc said:

I rememeber reading 10 weeks before it starts to solidify in your lines (areas where the fuel is in small volumes).

I also have been 95 RON has a better shelf life for both performance and storage, providing your comp isn't too high. 

What fuel do you use @Peter M

As far as I know fuel octane and detonation resistance aren't directly corrolated. You can have lower octane fuel which doesn't detonate either. 

rminc,

In the context of PFA and the majority of readers having fuel injected cars from the mid 70's onwards.

The fuel lines on these cars are normally maintained in a closed pressurised state meaning that evapouration of fuel is negligible and there is really no risk of viscosity increase or solidification.

I've also seen posts claiming 95 RON being more stable and somehow better than 98 RON.  However I haven't come across any plausible data to support this.  There also isn't anything in the Australian fuel standards that would indicate that 98 would be more unstable or inferior.  If people reported that 98 caused their engine to be harder to start, I could rationalise that but that's not being reported anecdotally. 

I've never noticed a difference between running 95 or 98.  Not saying there isn't a difference, it's just too subtle for me to pick up!

Depending on the car, the runabout gets the cheapest readily available 91 or E10 irrespective of brand.   My Ducati I prefer to run a name brand - BP, Caltex or Shell - 95.  My mildly modified air cooled Carrera with a measured 10.3:1 compression ratio, twin plugs, twin knock sensors through a Motec M130 ECU, I prefer to run a name brand 98.

Octane and detonation resistance are directly correlated provided the other factors that influence knock are held the same. 

Those other key factors are ignition advance, dynamic compression ratio, cylinder heat temp, AFR, inlet air temp, combustion shape/spark plug position and intake charge swirl/tumble (this last two significantly effect combustion speed.  The faster the combustion the less opportunity for detonation to occur.)   Modern engines manage these other knock related factors so well that they do produce high specific outputs on low octane fuel .  For example if an '80's  3.2 Carrera had the same specific output as a late model Honda Jazz, they would produce around 10% more power and on 91 RON to boot!  A standard 3.2 would detonate itself to smithereens if asked to produce more power on less octane.

So much for my intended 3 sentence answer! 

    

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Thanks everyone! @Peter Mand @rminc. I've also heard that 95 is a better fuel to run if these cars aren't been driven that much. I've never ran it though, as everyone has always said 98 is the way to go. I think the shelf life is a bit longer. 6 months before a drop in quality as opposed to the 1 or 2 months for 98.

From my research and correct me if I'm wrong. 98 will be fine to run even if it's a year old. After a month or two it might drop octane, so might not be the smartest to be putting around full throttle, but the car will run, start and drive as normal. 

Hypothetically if the fuel is say 9 months old, you'd be fine unless you were doing something like a track day. 

Also, I was advised that for long term storage, it's best to keep your tank full of fuel to avoid condensation. There are other benefits, but I've gone blank for now. 

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  • 9 months later...

Got my car back from a service today and was speaking to the mechanic about fuel. So I thought I'd reply to this thread. He recommended 95 instead of 98 fuel due to the static compression. There is no benefit in running 98 and he also said 95 has a much better shelf life than 98. I think with the US static compression you can even use 91.

I don't drive the car much and after a month or two 98 starts to degrade. 95 again has different characteristics giving you a longer period (around 6 months) before fuel starts to degrade, 91 again gives you longer (1 year approx). 

Just what I was told for anyone interested, so I'm going to make the switch to 98. 

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From what I understand is that the US fuel ratings are different to ours. Perhaps I’m wrong?

Also for example our BP98 is better than some other 98s. Some fuels with their additives are some what hydroscopic, these you’d want to avoid  for cars not being driven regularly.

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25 minutes ago, Joz said:

From what I understand is that the US fuel ratings are different to ours. Perhaps I’m wrong?

Also for example our BP98 is better than some other 98s. Some fuels with their additives are some what hydroscopic, these you’d want to avoid  for cars not being driven regularly.

For that reason I think 95 is actually better. Longer lasting. 98 is more for high compression engines. I think people just have the misconception that 98 is better, because it's 98.

Im not referring to 98 fuel ratings. Referring to US static compression for engine. I'm not sure if our cars are US or euro spec. 

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US uses the (R+M)/2 metric to measure octane, whereas most other places use RON, so the scale is a bit different. The US grades are usually 87, 89, and 91/93 (the highest grade varies a bit by region). US 91 octane is equivalent to Australian 95. So my US 1988 car which has a Steve Wong chip mapped for the US 91 gas/petrol takes 95 here. 

I don't know if this is true here, but in the US it's a legal requirement that a refiner's different grades all have the same additive package. If you go to e.g. a Mobil station, the only difference between their 87 and their 91 should be the octane rating. So while you might want to use a name-brand petrol for the additives, in normal situations there's no benefit to running higher octane than what your engine requires.

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On 18/07/2022 at 17:26, autojack said:

US uses the (R+M)/2 metric to measure octane, whereas most other places use RON, so the scale is a bit different. The US grades are usually 87, 89, and 91/93 (the highest grade varies a bit by region). US 91 octane is equivalent to Australian 95. So my US 1988 car which has a Steve Wong chip mapped for the US 91 gas/petrol takes 95 here. 

I don't know if this is true here, but in the US it's a legal requirement that a refiner's different grades all have the same additive package. If you go to e.g. a Mobil station, the only difference between their 87 and their 91 should be the octane rating. So while you might want to use a name-brand petrol for the additives, in normal situations there's no benefit to running higher octane than what your engine requires.

That is what I found. 95 is a better blend for my car, seeing its driven occasionally. Have been using it for months. Cannot see a difference between 95 and 98. It's also recommended to keep the rank almost full to avoid condensation. I would always leave it at half. Good fact sheet on BP website. 

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