On Sun, 25 Nov 2007 10:23:55 +0700, Bruce in Bangkok
wrote:


This "running one engine to save fuel" story has been popular for
ages, but I have always wondered about it.
...
Bruce-in-Bangkok

The run one, stop one approach is likely to succeed with
spark ignition engines. At low throttle they incur pumping losses
to keep that vacuum going in the inlet manifold.

Diesels don't have this problem, and so are less wasteful at low
revs.

Brian Whatcott Altus OK