I’m sure my distance to empty used to be accurate but now I lose about 40 miles from what it says when I fill up. Is that normal? I’m sure it used to be more accurate?

12 hours ago, Jason87 said:

I’m sure my distance to empty used to be accurate but now I lose about 40 miles from what it says when I fill up. Is that normal? I’m sure it used to be more accurate?

I'm pretty sure your memory is playing tricks on you. The only 'accurate' method is to do a full brim to brim top up with fuel, and manually workout your consumption. Then, every time you full up, set your odometer to zero, and then use that as a range calculator... Built in 'computers' are inherently inaccurate.

If you fill up 'early' a few times it seems to forget how big the tank is.  I've noticed this on a few different cars.  Like an old phone battery that had to be drained and fully recharged every time.

You can help it remember by pushing into the '0 miles remaining'...but only if safe to do so and if you're sure of the actual range.  I'm not recommending just randomly driving on the motorway until it cuts out lol.

I presume the distance to empty is calculated using the running average mpg. So after you fill the tank the distance to empty is variable. Mine can be anywhere between 630 and 700 miles depending on the type of journeys I've been doing.

Maybe I’m forgetting. I just thought the range is done on how you drive and I always drive the same so didn’t think id lose 40odd miles 

I’ve never understood how it calculates it. Does it look at mpg for the last mile or last 5 miles or last 25 miles or last 1 minute or last 10 mins or since you last started the engine?    Does anyone know?   Does it vary by make and model.  I would never rely on it.      Years ago a friend borrowed my brothers car. He ran out of petrol.  He said it wasn’t his fault as no warning light came on!!!!.   The car had no warning light but it had a perfectly good working fuel gauge.  To make things worse-   As it had a slight coolant leak my brother kept a container of water in the boot-  but it was a red plastic petrol can - with water in.   The friend assumed this was petrol and poured it all in the fuel tank.  A complete disaster . 

9 hours ago, isetta said:

... A complete disaster . 

My Uncle was a chief research scientist with GM in Detroit from the 1960 till he retired in 2000. I use to spend much time with him when younger, and always remember him telling me that if he could design a really accurate petrol gauge, he could make a fortune! It's all a black art involving witchcraft! LOL

10 hours ago, isetta said:

I’ve never understood how it calculates it. Does it look at mpg for the last mile or last 5 miles or last 25 miles or last 1 minute or last 10 mins or since you last started the engine?    Does anyone know?   Does it vary by make and model.  I would never rely on it.      Years ago a friend borrowed my brothers car. He ran out of petrol.  He said it wasn’t his fault as no warning light came on!!!!.   The car had no warning light but it had a perfectly good working fuel gauge.  To make things worse-   As it had a slight coolant leak my brother kept a container of water in the boot-  but it was a red plastic petrol can - with water in.   The friend assumed this was petrol and poured it all in the fuel tank.  A complete disaster . 

My grandad's car had a slight coolant leak when I was a kid.  Car was bought brand new, he just didn't want to make a fuss.  He carried around a 2 litre pop bottle with coolant in it...looked like Lucozade!  

I don't know how the range is calculated but I suspect it does differ between cars.  I've generally found it fairly accurate, once you learn that cars particular 'quirk'.  (The Golf range can't be trusted below about 50 miles...I reckon the previous owner wore out the bottom of the gauge by sticking a fivers worth in every few days.)  With the precision of fuel metering on modern cars, the MPG calculation should be pretty accurate.  It's the tank level that's still a bit poor, easily affected by parking on hills etc.