What would you expect to get to the gallon sitting at the usual 70-80mph on the motorway??

I drove my fathers 1999 2.0ltr Sport Automatic and the return was Dire, 29.8mpg [img]/ubbthreads/images/graemlins/confused.gif[/img]. I was expecting a good deal more, afterall My 735 (For Sale, before anyone comments!!) returns 30-34 at the same speed on the same long distance run [img]/ubbthreads/images/graemlins/smile.gif[/img](150 miles one way!) so I'd have expected something similar if not more than. Any Ideas anyone??? Its just been dealer serviced for 40k miles and no faults were found on the diagnostics...

I'd be interested to hear other opinions on similar Boras?Golfs..