Back in the 1960's my uncle bought a new full size Ford passenger car and was suprised that it got upper 20's MPG.
After the first scheduled maintenence it dropped down to about 14.
He brought the car back to the dealer and they assured that his car was working
properly:
That a "mistake" had been made at the factory and they replaced "parts" not meant for the car on his last visit.
They didn't offer any further details even after the (suspected) fuss was thrashed by my uncle.
Suprisingly he is still a "Ford guy".

Steve

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT