[alfa] Filling gas tanks

[C M Smith <cmsmith@xxxxxxxxxxxxxxx>]

When deducing how much fuel has gone in to you tank remember that the 
published capacity for fuel is for a completely empty tank. Generally 
speaking it is very difficult to get the last 10 liters or 2.5 gallons out 
of the tank in normal driving. The fuel gauge usually reads empty or nearly 
empty when you actually have a couple of gallons in the tank, for obvious 
reasons (i e no one needs to be informed by the fuel gauge that the tank is 
empty!). Most new European cars are set up to switch on a low fuel light 
when 10 liters remain in the tank (or 7 liters or whatever % of the tank is 
deemed appropriate by the designers, my SAAB's use about 15% remaining or 
10 liters enough to travel about 20 miles in town and 30 on the highway 
before the fuel starvation effects show up from low fuel).

A 12 gallon tank will rarely take more than 10 to 11 gallons on a refill 
when the fuel gauge shows  empty. Also, depending upon the shape of the 
tank and position of the pump intake the engine will exhibit fuel 
starvation symptoms considerably before the tank is actually empty. Put 
another way, there has to be enough fuel always in the tank to allow the 
intake to reliably pick up fuel so you can never refill with an amount 
equal to full dry capacity.

Finally, most fuel gauges are conservative, tending to be calibrated to 
show empty quite a bit before the tank is actually nearly empty. The most 
reliable guide to fuel remaining is to know your fuel economy and watch the 
odometer. I always use my trip odometer for this purpose when not actually 
using it for a designated trip. I have found the trip odometer to be the 
most useful instrument for gauging fuel remaining as, after all, what you 
actually need to know is how far you can go on the fuel remaining, not how 
much fuel is actually there. My SAABs have the nifty (and dead accurate) 
range to empty display as part of the on board computer. This requires a 
pretty accurate fuel level sender to be workable, and takes the consumption 
directly from the FI ECU and the mileage driven from the odometer drive.

Cheers


Michael Smith
White 1991 164L
Original owner
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