How Accurate Is The Mpg Computer?

[T20oer]

I've had my 2007 rx400 for a couple of weeks now. I've managed to achieve 35.6 mpg on a run and according to the computer im averaging 27.4 around the houses. But, I'm beginning to wonder how accurate the computer figures actually are.

I'm actually getting about 60 miles from £20 worth of juice, which in real terms is around 18 mpg. Which is shocking :( I'm not driving it fast or with a heavy right foot, in fact I've always got one eye on the mpg figures. It's a nice car but I don't think I'll be keeping it very long at this rate. I'm a bit disappointed really, I was under the impression the hybrid system helped the mpg figures ??

[katabrontes]

On my RX350 the computer shows about 20.7 but calculating on full to full and the trip meter give near to 19.8 running around the country at a fairly gentle pace. It was better on a fast run on the motorway (400miles) - about 26MPG - so it looks as if the computer is a bit optimistic. The service manager at LKexus Bordeaux told me that one should expect about 9L/100Km (31.4MPG) from an RX400 and about 8 (35MPG) from an RX450. He thought about 13l/100Km (21.7MPG) would be about right for an RX350

[T20oer]

I can understand official figures being exaggerated but the car lying to me as well? What is the world coming too?? To be honest I'd be happy if I was getting what the computer is telling me I'm getting but 18? I find that pretty hard to live with :(

I think I'll take it back and get it checked over

[nelmo]

.

I'm actually getting about 60 miles from £20 worth of juice, which in real terms is around 18 mpg.

You're being too vague there.

To check, do this:

fill the tank up (stop when the pump cuts out the first time)

Zero one of the trip odometers.

Drive until the tank is near empty (you could just wait until its half full but it won't be quite as accurate).

Fill up again to the first click.

Record how many litres you filled up with (X).

Record how many miles on the trip odometer (Y).

Calculate mpg using this formula:

Y

__________

(X / 4.546)

I've done this and found the display optimistic by 1 or 2 mpg only. But that may be my fault because I'm not filling up the same amount both times.

I get 18mpg when towing my 1600kg caravan so i doubt you're getting that low just driving round. Having said that, the RX is a 2 tonne, 3.3 litre, 270bhp petrol engined thoroughbred - you're not going to be saving the planet! :-)

[ISJason]

hi,i get 30 -35 around town and 35 to 38mpg on the Mway, so i'm pretty happy considering the size of the car. Helps if your not a fast driver too i guess. (not suggesting you are. )

I've never bothered to try to test the accuracy, as compared to my old IS200 at 29 mpg maximum, its amazing enough.