Pat, a cool running engine will have more fuel condense out on the "cold"
metal surfaces.  This condensed fuel will get sucked into the cylinder where 
it won't burn completely and then spat out the tailpipe.  Not good for 
mileage, emissions, or engine life (it washes oil off the cylinder walls).
The condensation on cold surfaces is the reason that a cold start requires a 
closed choke(carbs) or operation of the cold start injector to get enough fuel
in suspension to start the engine.  

Happy Motoring!! (I resisted the urge to say Cool Runnin Maan!)

Steve

Kirbyst@a1.rpr.rpna.com

'77,'81 buses
'67,'70,'74 bugs
'68 1602,'79 528I bimmers