How much petrol am I losing?

[5129frederick]

During this very hot spell we've been having I put £10.00  of petrol into my car.  The day before yesterday I had to drive it somewhere, and I swear it's at least a third gone.  I read somewhere that on a hot day, petrol does evaporate, but I'm not sure what that figure is.  Am I losing up to a litre a day in fuel being a hot day, or what.  Somebody did work out a figure, but I cann't remember what it was.  Any idea?

[right-then-petal]

https://www.google.co.uk/#q=petrol+evaporate

that link might tell you

[5129frederick]

Thank you.  It did help.  Petrol does evapourate on a hot day, but so little, it wouldn't even register.  My car tends to have an iffy fuel gauge when running on thin air.  £10.00 doesn't even take it above the low mark.

On a related matter, if you're going away on holiday, don't fill your tank more than two-thirds full.  You're probably weighed down with everything bar the kitchen sink, and filling up the tank with even more, you'll actually see the back of the car go down as you put more in.  A gallon of fresh water weigh 10lbs - petrol weighs slightly less - that's why it floats, but to all intents and purposes it weighs the same, so by putting an extra five gallons, you're carrying not far short of an extra half hundredweight, and all that extra weight lowers the fuel economy.  Wait until you're at your destination and empty the car before filling up.

[goldcrest725]

I would agree with that. However, being a lazy so & so. When I'm driving to/from Scotland. I usually fill to maximum capacity, because my car. A Renault Scenic 1.6 Automatic will do the entire journey. Some 436 miles. On one tank of fuel, without stopping to refill. And the fuel prices at Motorway services are horrendous anyway.

[soppysofty]

Try not to let your fuel gauge get below the quarter tank mark as, especially in older cars, you run the risk of drawing sludge and residues into the fuel line and, from there, into the fuel pump and engine.

This can block the fuel line and/or damage the fuel pump.

So far as running a car with half - full tank of fuel goes it makes no difference to the vehicles fuel economy but, driving with a half full tank means that you have to stop more often to refuel and it is the stopping/starting that consumes the most fuel.

Continuous driving at around 56 mph is the most economical but guaranteed to annoy every other motorist on the road.

I find that cruising at the speed limit on motorways and observing traffic so I do not need to brake excessivley gives me the best fuel returns.

Easy on the right pedal, quick on the left pedal and use the middle pedal only when you have to - that is the recipie for good fuel economy and has, to date, returned me an average of 35 mpg in a 2 ltr Ford Focus which is 10 years old and has over 120,000 miles on the clock.

[5129frederick]

Good advice - I could add to that.  Change down through the gears, not the break for added economy, and use the same gear going down a hill as you would use to go up it.  There is a 50mph speed limit going down a hill on the A249 heading for Maidstone.  I see vehicles tearing past me, and yet it's only a dual carriageway with a good few bends in it.  Even the "heavies" do it.  In the wet, it's sheer madness.  I'll automatically drop into third gear and let the engine slow me down to a steady 40mph until I'm on the flat.  Drive according to the conditions, and read the road.  If there are a set of traffic lights on green 150 yards away, it's pointless trying to beat them.  30' from them, you'll only have to break heavily as they turn red.  Just approach them at the normal speed.  I actually look out for red traffic lights ahead knowing that if I approach them at 25mph, it's odds on certainty they'll change to green as I get there, and I won't have to stop at all.  I could probably teach Jackie Steward a thing or two.  Any of you members of the IAM - Institute of Advanced Motorists?  If people want to play with their horns and sound off, it's down to them.  Ironicallyit was one of just two points my MoT failed on - the horn, because I never use it from one month to the next.  I'm thinking of rewriting the Highway Code and bringing in overall stopping distances in feet - NOT metres!  

Oh, if only everybody as as good a driver as me ...   Calm down everybody - that was a JOKE!!!

[mygreyangel]

Petrol gauges are most unreliable at the extremes.  

I work at at petrol station/repair garage, it's very common for the gauges to stick when a small amount of fuel is in the tank or a small amount is added to an already low tank