When buying fuel I always "fill to the brim" so I can reasonably accurately calculate consumption, but I read somewhere that it's a bad idea. (I use diesel, by the way, if that's relevant.)
Is bad to fill to the brim? If so, why?
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Possibility of fuel expansion (less so in this weather, I guess) and overspill onto the road. Two wheels and diesel fuel don't mix. I guess that's one reason...
Tim{P}
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Fair point, although I have always been filling right up for exactly the same reason as CP, and haven't had any signs of overspill.
(In winter do we get better value, i.e. a higher weight and therefore calorific value of fuel, for the same volume?)
Oz (as was)
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In cold weather you will get the same volume of fuel but it will weigh more. When I was a pilot we used to notice that when we refuelled from an airborne tanker that had been on station for many hours the fuel in it was so cold that when took a full load from it our gauges (calibrated in lbs) showed hundreds of pounds more than we would have expected from a refill from a bowser at ground level.
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AS
I find that intriguing as presumably the tank sensors do not actually weigh the fuel but instead measure volume and then apply a conversion factor. Can you explain in more detail?
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I find that intriguing as presumably the tank sensors do not actually weigh the fuel but instead measure volume and then apply a conversion factor. Can you explain in more detail?
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I was an aircraft engineer once, and I can confirm that you are right. Although the cockpit guages are in LBS, the sensors (usually 'hall-effect') are still measuring volume.
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Possibility of fuel expansion (less so in this weather, I guess) and overspill onto the road. Two wheels and diesel fuel don't mix. I guess that's one reason... Tim{P}
In an old Metro I used to drive, my Dad once brimmed the tank on a cold night, then I drove it the next day which was warm and sunny. I had parked it in the sun; when I got back to the car, petrol was squirting out of the tank breather hose, and there was quite a puddle around the back tyre.
If someone had walked past and dropped a cigarette end, it could have been bye bye Metro...
;o)
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Yes there was a recall on some models because of this.
I had a 'B' reg MG Metro and that had to have a new petrol cap in the first year or so of it's life. Said something like increased risk of accident due to fuel on rear tyre.
With diesel and frothing I'm not sure how accurate brim to brim filling is. What about non-level filling stations or manhole covers. Also tank geometry can play a part. I can fill my MGF (saddle tanks, passenger side filler) from the drivers side then top them up after 50 miles (before a long journey) and put lots more fuel in but the MGF has issues with over - filling/breathers as well,
Simon
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Weirdly enough i had a problem when doing my calculations of my fuel comsumption, on a motorway run i got 53 mpg, on the same way down i worked out using the same calculation only 45 mpg.
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Its not what you drive, its how you drive it! :-)
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The more fuel there is in the tank the more mass there is to carry about, so acceleration will be lower and consumption (in galls/mile) will be higher.
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L\'escargot.
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"Brim" doesn't actually mean to the point where it would spill out if you tilted the car - it means the point when the automatic filler cut-off is activated. That is when the bottom of the spout touches the fuel, ie 6-9" down the pipe.
I know it is possible to over-ride that, by clicking again, and also that garage pumps cut off at different points.
That is why for real accuracy you need to always refuel at the same pump.
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However many pumps are unduly sensitive and the cutout may operate even at the start of a fill, if the nozzle is fully inserted.
Oz (as was)
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The manuals for all my cars have words very similar to those in the MB W124 manual: "Only fill fuel tank until the discharge nozzle unit cuts out - do not overfill". It's worth checking your manual.
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Same here Roger. "As soon as the correctly filled nozzle switches off for the first time, the tank is full. Do not try to put more fuel in...."
Not sure how true this is though. On the past two occasions, the first time I filled the tank quickly the cut-out only operated after the tank spat about half a mug of petrol onto the forecourt. Conscious of this the second time, I filled more slowly, but the cut-off operated far too soon to the point where I got about another gallon in, and even then, the tank wasn't as full as the first time. Incidentally, it was the same petrol station.
I can't see what problem filling to the brim would cause, as long as its not "overfilled" so that when it heats up, it expands and leaks out. As for the more weight idea, I can see the meaning, but surely on the whole, it doesn?t make that much difference. Even in my lightweight Polo, I can?t feel any real difference.
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I may have dreamt this so I wait to be corrected, but don't modern engines have a emissions filter (charcoal?) somewhere in the circuit that doesn't like being constantly soaked in fuel which will happen when you overfill the tank? Certainly both our new Vauxhalls say fill to cut off and then no more than a couple of litres more.
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Here it is from Volvo cars - note overfilling warning:-
Evaporative control system
The car is equipped with an evaporative control system, which prevents gasoline vapor from being released into the atmosphere.
The system consists of a fuel tank with filler pipe and cap, two rollover valves, a Fill Limit Vent Valve (FLVV), vapor vent lines, a charcoal canister, a purge line, and a purge control valve and engine connections. In addition, there is a pressure sensor connected to the fuel tank and a filter-protected Canister Close Valve (CCV) on the atmospheric side of the canister, for system diagnosis.
The gasoline vapor is channeled through the rollover valves and the FLVV via the vapor vent lines into the charcoal canister, where it is stored. When the engine is started, the gasoline vapor is drawn from the charcoal canister to the engine's air intake system and into the combustion process.
NOTE:
Overfilling the fuel tank can cause damage to the evaporative control system.
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No, you haven't dreamt it, my old Polo has this too. But as far as I?m aware, it sited quite far up the filler neck, so you'd have to be going some to damage it. Probably those you see with the filler nozzle just in the tank, trying to get every last drop in there, are those which are most at risk of damaging that.
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I thought all diesel owners filled to the brim, and beyond, that's why petrol station forecourts are always covered in sand.
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For some reason on our Citroen C5 diesel it stressed not to keep filling after the third cut out. Not sure if this is relevent.
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In my Saab TiD handbook it says stop filling at the first cut out...
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You will never fill a tank completely;for many years now(80s)there has to be an expansion space left in the tank(legal requirement)most manufacturers comply with this by not connecting the pipe to the highest point in the tank;the evap canister is normally connected to the system near the filler but there will be fuel traps to stop liquid fuel getting to the canister.
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At some pumps my diesel Passat causes them to cut out straight away. So I have to twist the nozzle around to stop that.
I usually top up to the filler neck as I can get another 10 litres or so in. Some fuels are so frothy I just give up.
Never had problems with overflow in hot weather with my cars.
Once my fathers's 1968 H120 Rapier did it and a large paint blister blew up. Fortunately it subsided when the fuel dried off.
Still got the blessed cap here, on my desk.
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I wasna fu but just had plenty.
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