What mpg figure does the trip computer use to calculate the range??

 

It uses the mpg figure displayed, and then uses information provided by the fuel tank sender to estimate the remaining fuel in the tank. By multiplying the fuel remaining by the average mpg, the range, or miles to empty, can be computed.



edit by Ron A: This is a revised reply since my first reply did not accurately state the method used.

 

Something to add is that the range is an ESTIMATE based on your recent average mpg. An easy way to consider the issue is that you can be sailing along for 250 miles on cruise control and be told that you have 150 miles to empty, but if you suddenly slam into a traffic jam (say, the Lincoln Tunnel at rush hour), the miles to empty figure is going to drop big-time because your average mpg is going to drop.

 

Ron - I know mileage and range have been covered on countless threads, so excuse this different slant on the same question.

I'm one of those guys that fills the tank to the very top. When refueling after the low fuel light comes on, the pump initially shuts off at about 13.5 gallons. I regulary can fill it to 16. Won't the tank/filler tube actually hold almost 19 gallons? That being the case, at 32 mpg (Hwy), I've got almost 600 miles in range.

I know there are multiple issues with completely filling the tank, but I have been doing it for 30 years, and have never had a problem. Remember, I'm a dinosaur from the mid-70's who went through two gas crisis. When you had to wait in line for an hour to buy a maximum of ten gallons, you dribbled every drop into the tank you could.

 

gurneyeagle: I don't know if you have seen my post about how much the fuel tank holds, and other info, so I'll repost it here. It also links to a couple of threads that will give you more information, if you care to go that far.

I used to do as you do, and I believe I have been driving longer than you, but after I did my test I found out that stopping at the first click will give you 17 gallons, and that is what the manufacturer intended. I believe that squeezing in any more might be detrimental to the emission control system.

This info is excerpted from a very long thread I started about fuel tank capacities, etc. and is based on actual and precise testing.

a. When the low fuel warning light comes on, if you are getting 25 mpg you can go 94 miles, but if you are only getting 20 mpg, you can only go 74 miles. Of course, other miles per gallon figures will result in different results. This means you have approximately 3.7 gallons remaining.

b. When “miles to empty” (2004TL) or “range” (2005TL) reads zero, that is time to fill up, but you can still go 57 miles at 25mpg, but only 45 miles at 20mpg. This means you have approximately 2.3 gallons remaining.

c. When filling the tank, if you stop at the first shutoff, you will have about 17 gallons in the tank.

d. The tank will actually hold about 19 gallons, but it is not recommended to fill the tank to capacity, so stop at the first shutoff.

If you want to read the whole thread, click here. and if that's not enough information for you, here's another thread you can read.

 

Thanks for all the information. Very educational. This is an excellent forum.

 

From personal experience I noticed that the time your car idles is also included in the MPG counter. This is easily visible if you reset your trip computer. You will see a drop for every minute you stand in traffic or on traffic light. So speed, distance, time, manner of driving are all considered.

 

Thirty years ago cars didn't have sealed fuel systems with evaporative recovery cannisters that can flood (and potentially ignite) if the tank is overfilled.

 

That makes sense when you think about it. Your car still burns gas when you're sitting in stopped traffic—that's one reason why metered taxis usually charge at a specific rate for time spent stuck in stopped traffic. You're averaging zero mpg when you're stopped like that, so your average mpg drops.

 

You may have been topping off for the last 30 years, but only in the last 3 years did the feds mandate complex systems to test that the gas tank system holds pressure....test pumps, valves, charcoal canisters, vapor recovery systems, etc, and lots of raw fuel into those parts over time will cause problems.

Brett

 

Thanks for that info, Brett.