18 month old gas in the tank - what to do?
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If the gas was bad, you would know within 30 seconds of starting the engine. It's mostly a myth that gas goes bad over time handed down from the days when cars had carburetors and fuel tanks that are vented to the atmosphere allowing the fuel to oxidize in place. I'd be more concerned with moisture in the tank which could cause the fuel pump to seize up, but since you drove it a few times, that wasn't an issue. I have many cars in long term storage and try to start the engine every 3-6 months and run it a good 30-60 seconds to keep the fuel pump free.
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Yep - I had boats for 24 years and had a couple tanks go south …
It would be my second concern, with varnishing being the first. We know it hasn't varnished.
I don't know what sort of knock sensors an 88 porche has, so I wouldn't flog the car until the gas gets used up. Yes, drive it at the speed limit, but take time getting up there.
Just drive it. Don't over think it.
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Thanks for all the replies! Just to be clear, at this point I'm not stressing about this since the car is running fine. You guys should have heard some of the people on the Porsche forum when I asked - telling me to drain all 60 liters, "It's the safest thing to do," etc. I just wanted to hear some more technical commentary about gasoline aging and when/why it might matter, because there is SO MUCH vague speculation out there. I'm a curious nerd, that's all. To respond to a couple of other comments:
The car doesn't have any knock sensors, so even though I did add a bottle of octane boost, I've made a point of not flooring it etc.
It did seem like gradually diluting the fuel wasn't going to be helpful - it's not like the fresh fuel was going to somehow restore the old, especially if it had really turned gummy or watery, etc.
I did assume that the 12 month timeline on the stabilizer was just a guarantee, after which the effects would decline, and 18 months didn't seem too far into the future.
The car doesn't have any knock sensors, so even though I did add a bottle of octane boost, I've made a point of not flooring it etc.
It did seem like gradually diluting the fuel wasn't going to be helpful - it's not like the fresh fuel was going to somehow restore the old, especially if it had really turned gummy or watery, etc.
I did assume that the 12 month timeline on the stabilizer was just a guarantee, after which the effects would decline, and 18 months didn't seem too far into the future.
There are various fractions. Petroleum is refined via fractional distillation. If you've ever seen a refinery, all those pipes you see are really distillation columns. They're attempting to separate different components by molecular weight. The lighter molecular weights will be considered "light ends". Then once they have different weights separated, these get blended into the finished fuel.
Octane rating isn't really a matter of octane leaving or degrading. Octane rating is relative to a standard of a blend of iso-octane and n-heptane. Pure iso-octane has an octane rating (MON or RON) of 100. n-heptane has an octane rating of 0. Blending them together is the reference test fuel But finished gasoline doesn't necessarily have any octane in it. It's just an abstraction. But when various hydrocarbons and oxygenates break down, the result is more likely to knock - aka the octane rating lowers.
I'm not really all that sure that 18 months is that bad, especially with a modern, sealed vehicle fuel tank with modern emissions systems. Not sure how a 1988 vehicle fits into it, but I would think it would have a sealed emissions system where the empty space in a tank is filled with fuel vapor instead of air.
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Thanks, this is really clear and explains even more about octane rating than I already knew - I was just recently explaining the basics of octane in an informal class/teaching setting, but I described it as an additive that prevents detonation. I always like to know these details, even if I probably won't try to explain it to people this way
It does look like the car has a vapor recovery system of some kind, so good to know that it would also play a role in the longevity of the gas.
Thanks, this is really clear and explains even more about octane rating than I already knew - I was just recently explaining the basics of octane in an informal class/teaching setting, but I described it as an additive that prevents detonation. I always like to know these details, even if I probably won't try to explain it to people this way
It does look like the car has a vapor recovery system of some kind, so good to know that it would also play a role in the longevity of the gas.
I’m not an expert on this, but I have heard of “octane content” being used to describe “octane rating”. But octane is just the reference. I’m not quite sure how it works over 100. But this is a list of octane ratings for various fuels.
Octane rating - Wikipedia
With storage, others mentioned oxidation, which obviously can be reduced if oxygen is limited. I’m pretty sure there’s other type of breakdown, maybe dependent on temperature.
It has everything to do with how the rating is obtained and what may or may not be added to iso-octane. I know you know there are multiple ways to do so.I’m not an expert on this, but I have heard of “octane content” being used to describe “octane rating”. But octane is just the reference. I’m not quite sure how it works over 100. But this is a list of octane ratings for various fuels.
Octane rating - Wikipedia
en.m.wikipedia.org
With storage, others mentioned oxidation, which obviously can be reduced if oxygen is limited. I’m pretty sure there’s other type of breakdown, maybe dependent on temperature.
And here was my response to you on the "over 100" thing a while back:
A Reason to Buy Premium Fuel
My 17 Regal GS calls for ETHYL. :D I called for Ethyl once..... But she never returned my call. :cry:
bobistheoilguy.com
I have seen that claim before but I do not know how that is possible. Depending on the definition of "stale" there is no way any additive is going to reverse oxidation.
Help to prevent it? Sure. Reverse it? No way.
I agree. But the claim is right there on the bottle' s front label and on their website. I have heard good things about it from my boat buddies. I use it in my boat but I don't know if it has done anything, the boat always starts and runs good, even with E0 from last season.
Does the gas tank have a drain plug, my '88 BMW had one,
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