2012 RX 450h Curious about the Range declared by the on-board computer

[TRWeasle]

I am new even for a newbie, both to Lexus and to the world of Hybrid.  

I have driven just over 2k miles with my new second hand Lexus and was wondering about the declared range and the fuel gauge of the car.  
Often the car has been giving me a low range like 30 miles left and then I fill it up and it will only take 52 liters.  In the manual, it says 65 liters capacity.  

Yesterday I really overdid it and the car was screaming at me 8 miles left.  I still only managed to put in 57 liters.  

A friend of mine (with a 2012 RX 300) said there must have been gas in the tank preventing the extra fuel from going in, but that I must have actually been pretty darn empty.  

What are your thoughts/experiences with this?  Is the declared range/fuel gauge accurate or have I got many more miles range than it tells me? 

I'm finding the range of the car -370 / 380 miles to be a bit stifling: I used to have an Audi A6 Avant TDI with a fuel tank of 80 liters and a range of 500 miles.
 

[Herbie]

But your Audi didn't have a 3.5 litre V6 petrol engine and weigh 2 tons did it?

The absolute most I've ever had out of a tankful in mine has been 390 miles, which is very good for a car of this size and weight.

[TRWeasle]

2 hours ago, Herbie said:

But your Audi didn't have a 3.5 litre V6 petrol engine and weigh 2 tons did it?

The absolute most I've ever had out of a tankful in mine has been 390 miles, which is very good for a car of this size and weight.

Lol, no it had a 3.0 Litre V6 diesel engine and weighed only 1.8 tons.  

My question was not actually regarding the range, but more about the *accuracy* of the range shown on the display of the RX 450 h. 

[Nigel-Lexus Owner]

Hi Amit,

The best is to fill the tank up as soon as a low fuel light come on. The fuel protects the inside of the tank and lubricates the fuel pump. If you are able to get only 57 litres maybe there are 8 litres left in the tank which are needed to cool and lubricate the fuel pump. If you are so brave, maybe get a full petrol can with you and keep driving until the tank is completely empty. Not sure if the engine will start with just adding fuel. Maybe it is easier and cheaper, just to go to a petrol station as soon as a low fuel light comes on.

On another note. If you are doing 380 miles from 57 litres of fuel, this is 6.66 miles for every litre.

If you have 80 litres tank in the Lexus you could do 533 miles. (6.66 x 80 = 533)

I hope that helps. I do not think you have an air in the tank, just Lexus does not want you to run empty, due to fuel pump potential damages, which might be a costly replacement and not a great relatability advert.

 

[jumpingjehovahs]

I read on here once that either there’s a really large reserve or the miles to empty is set too high so you’re less likely to run out. Something like that anyway.

Weirdly, I’ve always thought I can’t get enough fuel in mine and been surprised at how little goes in.


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[ISJason]

Just a thought. The RX is a long range cruiser. Surely the idea is to enjoy the luxury and the size . If you have to worry about the fuel and mpg so much, why buy one in the first place?

[malcolmw]

About the 4th Gen RX but...

 

[Herbie]

17 minutes ago, ISJason said:

Just a thought. The RX is a long range cruiser. Surely the idea is to enjoy the luxury and the size . If you have to worry about the fuel and mpg so much, why buy one in the first place?

I got mine for medical reasons after a back injury. Normal saloons are almost impossible to get into/out of and no other SUV came close to being as comfortable, so it had to be the RX. However, I'm not rich and running the thing is darn near killing me.

Not everyone who has a luxury car also has a luxury bank balance to go with it.

[TRWeasle]

4 hours ago, ISJason said:

Just a thought. The RX is a long range cruiser. Surely the idea is to enjoy the luxury and the size . If you have to worry about the fuel and mpg so much, why buy one in the first place?

Me?   I'm just exploring this world and discovering what she can do.  I've also hit 120 mph on the speedo with her, so yes, I am enjoying the luxury.

 

[Teshoo Lama]

5 hours ago, ISJason said:

Just a thought. The RX is a long range cruiser. Surely the idea is to enjoy the luxury and the size . If you have to worry about the fuel and mpg so much, why buy one in the first place?

Being new to the RX, all the comparison shopping is still fresh in my mind.

It's actually a relatively economical option when bought second-hand, given the high mpg for the class, low tax and exemptions (like the free parking permit in Westminster, which is otherwise £145. Then there's expanded ULEZ in 2021). It's also easy on the discs and pads isn't it? Those savings will add up.

Luxury and economy in the same package. I mean, what do other big, heavy automatic V6 petrol SUVs get? Low 20s per gallon at best. High teens on an equivalent Range Rover? I did 37 mpg from Lancashire to central London today.

[Brian26]

Hi All, I may be completely wrong here. But I remember back in the dark days when I had a Merc there was some discussion on one of their forums regarding how much was left in the tank when the yellow warning light came on. I seem to remember thst there was an EU requirement for the warning light to come on when there was enough fuel left to do a further 50 of 60 kilometers. (That being the distance between motorway services on the continent I believe ) . Maybe that would account for the large amount of fuel being left in the tank when the light comes on?

Bri

[darrude]

There are various reasons not to drain the tank as stated above, but an often forgot reason is to prevent fuel starvation when the car is on an incline and fuel is taken away from the feed point, more of a problem when parking on an hill, you come back then can't start your car. 

[Lost it]

The other issue is that usually the fuel pump sits in the tank. And it uses the fuel to self lube and cool itself. So there's always a "fudge factor" in the fuel gauge to try and stop people running the pump dry, wearing out everything in the process. Starting with the pump. It's not a "variable displacement" device with a controlled bleed to allow some fuel to return to the tank, it's a pump that pushes against a pressure setting system for the fuel injection.

Basically you should never run a tank dry. No idea how easy it is (or isn't) to get to this pump if it fails on you through you trying to get the last mile from your fuel tank.

And as for tank range, it's not an "active measuring" system is it? Doesn't it rely on the last journey type to estimate a range? So if you do a lot of motorway miles at 65mph average, it will tell you you have more range than if you spent the last tankfull crawling through central London at 13mpg or less.

Just guessing here.