The pumps aren't accurate? Like MikeShepherd stated litres and km is the only way to get accurate. I finally got my wife on this vehicle to help me document each fill up. I use fuelly. My experience is that each tank is different, depends on whether it was city vs highway for that given tanks. On our long road trips, the vehicle was quite off. The lifetime of the vehicle isn't too far off though. My signature has a link to our real world numbers.

 

Accurate pumps?

I am saying when you fill up, especially an RX how do you make sure it is filled exactly to the point you filled it last time? Impossible.

 

For me the RX software in calculating (litre per 100km/mpg) is good enough for my purposes, there of course is nothing wrong in doing more detailed calculations if you wanted to now exactually the amount used verse distance traveled. It would be interesting if someone has used both methods while driving the same route to see what variance there is. Cheers

 

I have 7500 miles on my RX 350h. I manually compute the mpg each time I fill up and reset the trip computer. Sometimes my manual calculations are a mile or 2 more than the vehicle shows, sometimes a mile or 2 less. As such, I think the vehicle computer is pretty accurate. As indicated above, even though I fill up each time, the actual level that is put in the tank is going to be different each time due to fuel flow, weather,etc. There is no way you can accurately manually compute mpg since you can’t see the exact level the fuel in the tank is each time you fill it like you can a 5 gallon gas can.

 

‘How do you fill to the exact same level each time?

 

You can’t, as my post said. That’s why manual calculations are not perfect. I agree with your initial post.

 

This is a good question, to many variables from tank fill level, nozzle shut off pressure, weather temperature and so on. The best we can do is try and eliminate discrepancies to the best of our ability. When the low fuel light comes on, it doesn’t matter how much fuel is left in the tank. It’s how consistent the fuel meter senser is to trigger the light. This is a variable we can’t control and have no idea what tolerances it functions at. This however should be our starting point knowing there is a margin of error.

Add fuel to a controlled volume, do not fill the tank to the top, for example say 8 gallons. This can be repeatable at the same gas station using the same pump under similar weather conditions. When the low fuel light comes on calculate your milage based on 8 gallons.

This is just my thoughts, opinions, but I am enjoying the car.

 

Novel idea but many people may not be able to get to a station the second that light goes on. They may drive many miles before they get to a station let alone the same "repeatable" station. I think if you use the same brand with the same pump setting and stop after the 1st click off you can get fairly accurate and consistent.

 

If I were to simplify the process for the explanation above .

1) Fill your tank when the light goes on.
2) Write down how many gallons you added (it's irrelevant when you stop filling)
3) Drive car until light goes on.
4) Divide the milage by the amount of gas you already put in.

There is no need to replenish the fuel to figure out MPG

 

I thought we had computers to calculate MPG?

 

I have found in-car MPG calculators to be inaccurate, often optimistic.

There is no excuse for not maintaining a log so that you can monitor MPG over long periods, if you care about such things.

Granted, we come from the era of carburetors, where MPG was an indicator of proper health, that needed to be tweaked periodically.



Where is the idle mixture adjusting screw on the 500h, again???

 

I have a fuel flow meter in my boat. It is ridiculously accurate. I know there are log book apps, but they are way too much work. I am primarily interested in what is the ultimate range of my hybrid. Right now I *think* it is 900 kms. But I won't try to test it unless I bring along a jerry can.

 

It does matter when you stop filling. If the pump clicks off and you continue a few more times till it clicks off each time you will be adding more fuel which will make your mile calculation go down. If you are consistent and stop after the 1st click of each fill up it wont matter.

 

I doubt the above will yield accurate results either. The kick-off device on the pump hose can vary depending on how far the nozzle is inserted and how it is inserted and the speed at which you are filling your tank. . Plus I doubt they are all calibrated the same. The device would/could have different results from one pump to another. Also speed of fuel being added has much to do with it as if I pump at full speed, the device will kick off immediately on my 350h even when I am close to empty.

 

This will impact the results for single tank fills, however, if you track over the long term it will have no impact. As a retired Engineering manager, people who know me would expect me to have a spreadsheet for this, and I do! When I fill my tank I record my total mileage and the display MPG on the credit card receipt. I put this in a spreadsheet later. The actual vs. display MPG values are rarely the same and they are not off in any direction + or - more than the other.

The spreadsheet I have now is for my Mercedes GLE 350 which I am trading for a 2024 RX 350h which should go into production any day now!!!