On 2 December 2012 16:38, SUSANC <SKCHANDLER4@hotmail.com> wrote:

We have had two motorhomes based on the 2.8jtd Fiat and both of them ran
at about 55 mph when at 2000 revs. We have just got a used van based on the
same engine and find that at 2000 revs it is running at about 47 mph. This
van is 1 metre longer than our others - could this be the difference or
could it be a sign of something else? As we do about 9000 miles a year will
this make a great difference to our fuel usage? Any info greatly
appreciated.

I'm not a Fiat man, but using my Land Rover experiences there will be
differences.

The gearbox may have different ratio gears.

The axle differential may have a different ratio.

The tyres may be different sizes, so their circumference would be different.

Then the speedo could be wrong. Try using a GPSr to display actual
speed over the ground. Used correctly, a GPSr will always be more
accurate than a speedo.

Reg