Log in

No account? Create an account
spikey eye bw



Musings, questions and brief essays. The normal.

Previous Entry Share Next Entry
Car and fuel question
spikey eye bw
So I have filled up my car several times now, they have a tendency to drink petrol. I'd had no problems the first few times. Then, a couple of weeks back I had a few passengers and when I tried to fill the car would take a small amount of fuel before the pump cut out as though the tank was full. It did this repeatedly, taking about 70p - £2 of fuel at a time. Eventually, when the cost was what I expected to spend, I stopped. I had tried several different angles of pushing the hose's nose into the fuel tank, don't think I was doing anything different. I wondered if the car might be at a weird "laden" angle with all the passengers and asked them to get out, to no avail. So I put it down to a dodgy pump.

Today I just went and fuelled up at that same station, but a totally different pump and it's doing exactly the same thing. So, either my car's got something weirdly wrong with it, or I'm doing something stupid. My bet's on the latter. Any clues what it might be, anyone?

  • 1
It's the automatic fuel cut off for when the pump thinks the tank is full - if it detects any kind of back pressure the pump will stop fuel flow.

Some pumps are more fiddly than others and it's purely an angle thing - so you have to keep playing with trying different angles and the like. You'll certainly find that if you have people in the car the angle you need to put the nozzle in at will be different.

The only thing is to keep trying and it will sort itself out. I get this all the time with hire cars.

I don't remember the behavior of the pumps being different in England, but I only drove there a couple of weeks, compared to 30+ years in the US, so consider this to be USA-based advice. (I suspect the auto cut-off on the pumps is essentially the same hardware in both countries, too.)

I've never found the tiny difference that load makes to make any difference in filling the tank. There's more difference than that in slope of pavement in filling stations. I am always careful to put the nozzle "straight" in to the filler opening, which may remove some variables.

The shutoff is back-pressure based, so if something is restricting fuel flowing into your tank somehow, that could cause this symptom.

This kind of happens to me at random. I wouldn't worry about it.

I think what is happening is that fuel is not going down the pipe (in your car) efficiently and the pump is cutting out because it thinks the tank is full.

So what I do instead is try to deliver the fuel at a slower speed by not gripping the pump so hard. That seems to work.

You could possibly pull the pump back a centimetre or two. That may help as well...

No, I bet it's the station. There's one station in Reading that has hair-trigger fuel cutoffs, and all the pump handles in that station do it. I just have to hold the trigger with infinite delicacy to keep it at the angle that neither stops because I've released the trigger, nor stops because I've pulled the trigger too hard and frightened the pump.

what they all said.

I look at the fuel gauge before filling, and most petrol tanks are 50 or 60 litres, so if there's a half tank of fuel, I can get at least 25 litres in there ... if it's nearly empty, I can get around 50 in there (and actually, a 50 litre tank will probably take 55 litres if you try really hard).

What they said about using less pressure (happens to me all the time, if I try filling at full speed, the air rushing out of the tank triggers the back pressure sensor and stops the pump ... so I just have to fill slightly slower so it doesn't cut out)

"...most petrol tanks are 50 or 60 litres..."
I think you'll find that petrol tanks vary wildly from 30-40 litres right up to multiple, 100+ litre tanks depending on the make of the vehicle, the engine size, how economical, the position of the stars and moon when it was designed, the designers favourite colour, etc.

A Ford Ka has a 40litre tank, Peugeot 106 45litres ... most of the cars I've driven have been between 40 and 60 litres.

But then I've mostly driven larger cars.

The car I have outside at the moment has something like a 90 litre petrol tank and a 100litre LPG tank :-) It's a LPG conversion Jaguar XJ6

I should have said "most petrol tanks (in cars hawkida is likely to drive) are 40-60 litres" probably.


It's a Rover 111. I think it has a 40 litre tank, it may be smaller.

You're right. Different websites have values from 33-40litres for a Rover 114

e.g. this site has two people discussing whether it's 36 or 33 litres.

I've never owned a car that size (though I've had them as company cars and loan cars while mine was being repaired) ...

... and obviously they tend to get far better petrol mileage than my big "tanks" do, and park in much smaller spaces.

Not you. Dodgy pump. Worry not.

Yes, wot they all said - have experienced this on and off for decades.

As has been said, (in a roundabout way) it's an excess of back-pressure that's supposed to be caused by the petrol in the tank reaching the tip of the nozzle. It's a safety cutout.

Unfortunately what can happen in practice is the pump feeds petrol in so quickly it doesn't have time to drain the neck of the tank before the neck back fills. It's not uncommon on smaller cars which tend to have a slightly narrower neck on the tank.

The way round it (as has been said) is to not squeeze the grip quite so hard (fnarr-fnarr) so the petrol doesn't flow in quite so vigorously.

Yeah tell me about it mine does this all the time, and its a very small car as people have just put petrol in slower and it is fine.

This happened to me spectacularly once when on holiday in the US and visiting the only petrol station that we could find whose price was less than some psychologically important whole number of dollars per gallon. It must have taken me about 20 or 25 "squirts" to get any half-decent quantity of petrol, regardless of whether my squeeze was tight or loose. We concluded that the station might actually have been close to out of petrol.

You might have a blockage in your fuel tank breather pipe. This is an air vent in the fuel tank which releases the air pressure in the tank when the fuel goes in.

Best to get it looked at. Better safe than sorry.

  • 1