Stale fuel

[swedishandgerman]

It should still run even on the most stale of stale petrol, just not so well. And it should start, just not so easily. I'd check all the basic stuff starting with ignition electrics.

Petrol loses combustibility as the octane rating reduces. However, it takes yonks to reduce to zero combustibility. High octane fuel (97 RON and above) reduces at a higher rate than standard unleaded (low octane 95 RON). Once high octane petrol has reduced to about 95 RON, the rate of reduction is the same from there downwards. Very high octane petrol (100 RON +) reduces to 97 or so quite quickly.

As such, if you set your car up to run on high octane fuel like I do, you are more likely to experience reduced efficiency, even pinking, after the thing has been laid up for a few months. But the thing will still run. If you set the car up to run on low octane standard unleaded with less ignition advance, you'll experience less noticeable effects.

There's not a lot you can do to overcome these effects. High octane fuel (97 RON or so) at the pumps - Tesco Optimum, Shell V Formula and so on - reduce quickly and ultra high octane reduce even quicker. Petrol with additives reduces quickly too. So if you use high octane fuels, the best thing is to buy little and often. In theory, you could regularly add octane boost, but that's a bit of a difficult one to monitor! I'm dubious about in tank octane stabilisers because there's no way you can reduce octane loss.

On the contrary, ethanol protection (to protect all the little metal parts) and lead replacement from out of the bottle additives don't reduce, so good to put in there.

These Volvos will run brilliantly on ultra high octane fuel but you have to adjust them to do so. As well they will run happily on quite bad fuel, but you have to adjust them to do so.

All based on the most efficient combustion happening just before pre-ignition (pinking), you can run them with 36 degrees max advance on the modern equivalent equivalent of 5-star (Super Unleaded 99 RON plus octane boost which adds 2 octane numbers = 101 RON).

Super unleaded is a bit higher than the old 4-star. You can run them on about 34 degs max advance before there's any pinking.

Premium unleaded - that's the standard unleaded you buy at the pumps - is about 95 RON so marginally better than the old 2-star. If you can run that and not experience any signs of pinking having set up your timing "by the book", then you're lucky. You usually have to knock it back a bit. And knocking it back a bit is not what I like!

Based on the above, if you set it up at 36 degs and the octane rating drops back after a few months, it'll pink and you won't enjoy as much power and efficiency as you could with fresh fuel in there.

[Ron Kwas]

Forum;

...good info from S&G and Derek!...yes, fuel deteriorates, and if you analyzed it with lab equipment, measurably in three months, but not anywhere near to the point of preventing ignition and Starting!!!

Often a squirt of fuel into the carbs will help awaken a car which was fine when parked a while ago, but which is reluctant to fire up (being vented to atmosphere, Fuelbowls will have evaporated empty)...this is my recommended Starting procedure with fuel which is older than a year (along with disabling ignition and cranking to build Oil Sys pressure)...after engine is running, Fuelpump will maintain fill of Bowls, and it will happily burn the old fuel (some pinking/pinging can occur if timing was adjusted right to the optimum edge [fuel has lost some of its anti-preignition properties], so don't do any performance tests or high load runs with it)...its also good practice to top up the tank once started with fresh fuel to pep up the old stuff...

Cheers

[Groundes-Peace]

Thanks for all the comments on this topic.
I cleaned the plugs and did use "Easy start".
The starter motor had to crank the engine for a lot of attempts before the engine started to reluctantly fire. Once warmed up the engine then ran smoothly whilst I replaced the air filters before driving to my nearest Shell garage.
I filled up with the "Super" they produce which I believe is 97 octane. The car is now running smoothly and restarting is no problem.
I keep my car in a brick garage, but I can see due to the recent variations in temperature in our part of North Bucks, the amount of condensation on metallic surfaces is considerable, with the car having been as cold as -8C then relatively quickly raised to 10C when there is high humidity in the air, I think this can also be a factor...

[tdz840]

Originally Posted by Simmy

todays petrol with ethanol added can eat away at rubber fuel lines on older cars. check float bowls and jets for debris

Yep good advice that i have just experienced.
Smally bits of rubber in the float valve and fuel chambers. Replaced the rubber lines and then split the old ones to see if i coould see evidence of breakdown. Nothing.
But a small inline filter I temporarily installed says different.
Blow through your carbs with particular focus on the float valve.
Russ