Old petrol in the tank

[bungeejumper]

An issue that might also be of relevance to some PHEV-ers who mostly plug in . I've just realised, to my not very great surprise, that the last time I filled my tank was last December. And the gauge says I've still got a third of a tank still in there, after doing less than three hundred miles.

Which, according to some people, is a problem, because six month old petrol is starting to generate what they attractively call varnish. Which, apparently, is double-plus ungood for your pump, your pipes and your fuel injectors.

I am pretty sure that my mileage is likely to rise significantly now that summer's arrived. But what would you do with the situation?

(a) Top the tank up to full right away, so as to dilute the separating petrol, and then thrash it off?

(b) Burn off the 1/3 tank quickly before I top it up?

(c) Get the tank drained? (Naah, probably not. If there's a layer of varnish at the bottom, it'll probably stay there, and anyway the outlet pipe to the pump is an inch or two above the tank sump.)

(d) Stop worrying and get a life?

BJ

[Dod101]

As a total non techie you can imagine my response. It would be to do (a) and (d). Plus probably try to use my car a bit more as lots of other stuff can go 'off' if the car is sitting virtually unused for 5 months or so.

Dod

[Mike88]

I have used one of my cars with petrol over a year old and it has been fine. Do nothing would be my suggestion.

[88V8]

......six month old petrol is starting to generate what they attractively call varnish. Which, apparently, is double-plus ungood for your pump, your pipes and your fuel injectors.

The problem is the ethanol content.
For old cars, pre-2000 say, the problems include fuel system corrosion and degredation of rubber parts. (I wrote' rubbers' then thought better of it).
This is a major issue for those of us running classic cars.
If you are interested, the Federation of British Historic Vehicle Clubs has produced a paper on the topic https://fbhvc.co.uk/fuels

Anyway.... modern cars have ethanol-resistant components, but ethanol rapidly evaporates, and when it evaporates the octane value of the fuel declines. This can make winter cold starting difficult.
If you have a performance engine, this can lead to damage from pre-ignition, but more likely the ECU will detect that you have dodgy fuel and dial down the performance. If the engine is more of the lawnmower variety, that will not be a problem.

And then... there's the hard deposits known as 'varnish'.

The deficiencies of ethanol fuel have long been known, and some manufacturers are more alert to it than others.
Toyota recommends adding at least 20 litres of gasoline every 12 months. If fresh gasoline hasn’t been added in a while, the main display will flash a message telling you to add fuel.
https://www.theglobeandmail.com/drive/m ... in-hybrid/

So, yes, try to keep it fresh. Fill the tank, use it up, and then try to remember to cycle through it at least 6-monthly.
Old fuel... not like old whisky.... old wine.

V8

[tjh290633]

Both our cars have been getting refuelled once a quarter, or even 6 months. They are still running.

My mower sits in the shed for several months and still starts, sometimes needing two goes.

Don't worry about it. Anyway, can't you force a PHEV to run on petrol now and then?

TJH

[bungeejumper]

Anyway.... modern cars have ethanol-resistant components, but ethanol rapidly evaporates, and when it evaporates the octane value of the fuel declines. This can make winter cold starting difficult.
If you have a performance engine, this can lead to damage from pre-ignition, but more likely the ECU will detect that you have dodgy fuel and dial down the performance. If the engine is more of the lawnmower variety, that will not be a problem.

And then... there's the hard deposits known as 'varnish'.

The deficiencies of ethanol fuel have long been known, and some manufacturers are more alert to it than others.
Toyota recommends adding at least 20 litres of gasoline every 12 months. If fresh gasoline hasn’t been added in a while, the main display will flash a message telling you to add fuel.
https://www.theglobeandmail.com/drive/m ... in-hybrid/

So, yes, try to keep it fresh. Fill the tank, use it up, and then try to remember to cycle through it at least 6-monthly.
Old fuel... not like old whisky.... old wine.

Great response. Thanks!

BJ

[Mike4]

It is generally advised with small petrol engines stored unused for long periods (e.g. mowers generators etc) that the petrol in the carburettor is drained by turning the fuel tap OFF then running it until it stops, in order to avoid the 'varnish' problem. But here, the 'varnish' is residue left when the carburettor petrol completely evaporates and i don't think that will be happening in the modern fuel injection components in your super-efficient PHEV petrol engine.

So, probably a case of "move along, nothing to see here". A better place to find out if this is a real life problem or just a theoretical one would be the discussion forum for your particular PHEV. I bet there is one!

[DrFfybes]

I just sold a car that was stuttering until I put some fresh fuel in. The BMW has similarly not been topped up since July and done 300 miles since, including the monthly jaunt on the drive.

The thing is to run the engine occasionall, even on a PHEV you can run it pretty easily if you choose - so best to choose to do it when the car is used.

My monthly procedure with stood cars is to wind the windows up and down, rotate the heater controls (vent choice, aircon pump, hot and cold, fan speed), warm up to operating temp and drive up and down the drive.

Just think of it as a stored classic with a large backup battery

In the meantime, shove a slug of Redex or similar in and try and use some fuel a bit more often. Top the tank up occasionally, and consider Super fuel as it has less (or no) ethanol.

[AF62]

and consider Super fuel as it has less (or no) ethanol.

Funnily enough I was just watching a video yesterday on steps to take when storing a car over winter, and this was the recommendation - a full tank of super unleaded, with the argument being that would minimise the amount of air in the tank.

[MonsterMork]

You could try jacking up the drive wheels, firing up the engine and sticking it in gear. That might work.

https://youtu.be/bqjK6jjt6gk

Please, please DON'T try this at home!!!

And more seriously, please don't try this at home! Having seen the aftermath of someone trying this and failing it really isn't recommended. And even when us professionals do it as a very-last-no-other-option method it is seriously pant-filling, even though we take a hell of a load of precautions to do so.

For a laid-up vehicle use a fuel stabiliser such as these:

https://www.frost.co.uk/sta-bil-fuel-pr ... zer-236ml/

https://www.frost.co.uk/millers-oil-tan ... rotection/

For those of us running older petrol engines try this:

https://www.frost.co.uk/ethomix-corrosi ... rotection/

MM

[9873210]

Cold starts are less likely to be a problem with a hybrid. The high voltage battery gives the equivalent of over 10000 cold cranking amps into a tens of kW "starting motor". If the fuel will run the engine you can probably start the engine.

Essentially the starter on a conventional engine is designed to be just able to start during the projected worse case, The "starter" on a hybrid is a secondary function of a system that is far larger because it is designed for other reasons.