Hi all!

I have bought 2002 S60 2.4 D (130HP) last month. I've made a test on the highway. I tried to achieve as low fuel consumtion as possible.
Conditions:
straight flat 80/50 km/mile long section of the highway
optimal engine temperature
booth directions driven test

My trip computer displayed average fuel consumption under 3 l/100km (80 mpUSg) in booth direction of the road.
Is it possible or computer is "cheating"?

J.

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Hi there. :grin: Presumably you zeroed all of the computers readings before conducting the test.

Diesel engines are economical, but a 2.4D pulling the weight of a Volvo S60 will not return 80 mpg over a 50 mile distance. In good conditions like you describe you may get very good mpg if you drive carefully on the highway/motorway but I still suspect that your computer is misleading you by a good 20% or more.

Instead of relying on the computer, I would fill the tank with diesel, do the test drive again, then refill the tank & do a calculation based on distance travelled divided by the amount of fuel used to refill tank the second time.

My other car is a 2.2 turbodiesel with a weight similar to that of an S60 & I get 50 miles to an imperial gallon on a long motorway journey (say 500 mile round trip). Without a turbo it might improve to say 60 mpg imperial. US gallons are smaller so the mileage per US gallon will be lower. :57:

:puzzled: I don't wish to be critical-but were you really driving over 80k's per hour when you took that photograph?

If you were-that was extremely dangerous and a very stupid thing to do. No trophy for that effort. :huh:

Naw, perfectly safe - looks like cruise control was on, so the car was driving itself, right? :excl: :o :wacko: :ph34r: :haha: :haha: :haha:

Sure, cruise controll will do ;-) As I described - empty saturday evening highway...
Anyway, as Black Beauty recommended, I figured it out from the diesel bills. Long time statistic (10000Km) showed, that fuel conpsumption was about 3,9l/100km, that's good too - it's the same as when computer shows 5l/100km and my real consumption is about 6.5. But 30% difference is pretty much, isn't it?

Come on, don't be ridiculous, 80kmh, watching the road and taking a blind shot... nothing dangerous... :auto:

:grin: Speedos are deliberately made to show a higher figure than is actually correct. This "tolerance" is built in by manufacturers mainly because the diameter of the tyres changes as the tread wears, as tyre pressure alters over time and as the tyre warms up/as the ambient temperature changes, when snow chains are fitted, when owners fit different sized wheels and/or different profile tyres, as other components wear etc.

For example the same wheel with a tyre having 7mm of tread on it will travel a greater distance per full 360 degree rotation than if it has a tyre with only 2mm of tread on it. Lower tyre pressure or a heavier load in the car will have the same effect. The difference in distance travelled will not be much per rotation BUT in percentage terms manufacturers err on the side of caution to stop your speedo under-reading your speed & you being convicted for speeding as a result.

Your electronic odometer uses this exaggerated speed reading to calculate distance travelled, so the distance travelled on a trip and overall on the odometer will be slightly higher than the actual distance travelled. The fuel consumption reading is based on the measured distance travelled & the measured amount of fuel used i.e. at least 1 of the factors in the fuel consumption calculation is inaccurate, probably both, therefore the read-out answer given as the current & average fuel consumption should be taken as a guide only, it is not completely accurate.

The most accurate way to measure speed nowadays is with a GPS device such as a speed camera detector (if legal in that country) or with a sat nav device. GPS systems normally give an EXTREMELY accurate speed reading when travelling at a constant speed - there is a time lag in the reading when speed is increasing/decreasing.

At a constant speed my company car's speedometer always reads 4 mph (around 6.5 km/h) higher than my GPS device shows. In my T4 the speedo reads only 1 mph (around 1.6 km/h) higher than the GPS device.

The most accurate way to check fuel consumption is to measure the fuel actually put into the tank versus the distance travelled using that quantity of fuel. The accuracy or otherwise of the fuel dispenser pump at the filling station and of the odometer will both affect the accuracy of the fuel consumption figure calculated but it is probably the most accurate way the average motorist can do this. The greater the distance that the calculation is based on, the more accurate the final figure is likely to be.

Sorry, but my guess is that 60.31 mpg over 6,214 miles of mixed city/motorway motoring is not achievable in your car. Depending on your driving style and many other factors too numerous to mention my guess for mixed/combined urban & motorway driving is between 42 mpg and 48mpg (imperial).

Happy & safe motoring!