I have a 1992 400 E
On a recent long journey (800km ~500mi) I got fuel economy of 8.9 litres / 100km (26.5 mi/USgal or 31.82mi / Imp gal)
My best city driving fuel consumption has been 12.4 litres/100km (18.93 mi/US gal or 22.73 mi/Imp gal)

This is the widest difference I've ever experienced in a car.

I've been trying to drive for fuel economy in the city, but apparently not succeding well.

Why the big difference?

On the highway, what engine rpm will burn fuel most efficiently?

Is running at best torque rpm of any benefit, or would slowing down to minimize wind resistance give me more.

Regards,
Vorpal

 

Hey Vorpal, there has been much info on this subject latly and a few key points to keep in mind for fuel economy for ANY car.

1. Tire pressure..this is a key factor, for many reasons...for proper tire ware, handling and fuel cons.
2. I heard on the radio that driving the posted speed limits in town, doing all your stops, you will save money on gas.
3. a lighter right foot, more cash in the pocket, avoid speeding from stop-to-stop.
4. on the highway, i hear that driving between 100-110 km/hour, you will save a bit on gas, anything over 120+km..you will consume more..
good luck bro.
Fabs

 

Hi Vorpal.
The big difference between Town and Highway is as follows.
Around town the engine has to accelerate the full weight of the car every time you stop. Reduce the number of stops and you will improve consumption. The weight of the car is also very important factor so a smaller, lighter car will give better fuel consumption.
On the highway it is all about rolling resistance and aerodynamics since the car continues to travel at a relatively fixed speed.
Rolling resistance is all about tyre construction (which covers width) and tyre pressure. Higher tyre pressures (within reason) improve consumption but worsen ride comfort, handling etc. Aerodynamics build up slowly throughoiut the speed range but are significant at anything about say 50mph.
You are correct in recognising that other factors also influence fuel consumption and rather than Torque one needs to know the speed at which the engine fuel loops are at their optimum. This is engine design and load related.

Big heavy large engined cars can be more economical on the higfhway than smaller engined cars due to the long gearing that can be used. However this is the reverse for town usage. Generally the smaller (lighter) the car the better since a greater proportion of mileage is usually done in town traffic.

Incidentally AirCon can contribute up to 10% reduction in fuel consumption when it is on. Try to turn it off.
Likewise driving style. Bad to Good.

If you are worried about fuel consumption / price try buying fuel in the UK at roughly 8 UDS for an imperial gallon!.