[Piwoslaw]

Originally Posted by RobertSmalls

We're talking about different pollutants here. If you allow your cat to get too cold, you're going to see a sharp rise in NOx and HC emissions as the cat doesn't function when it's cold. However, automakers were able to squeeze engine stop/start systems past the EPA, and some were able to achieve a SULEV rating while doing so. Whether this is an artifact of the EPA's testing methodology not representative of the actual NOx and HC emissions of hybrids, I'm not sure. It's at least an indication that engine-off is inoffensive enough that the EPA condones it.

Stop&Start systems are getting popular in Europe (I recently read that up to 70% of new cars will have it within the next few years), since it helps in the European fuel consumption test cycle, and helps to squeeze into the next-highest EURO emissions class. New cars have thermal insulation on their cats, which is a good idea for anyone who EOC's or drives efficiently enough to keeps temperatures low.

Thyme: I always understand that plain P&G is with the engine on, unless otherwise implied. But many members see it the other way around. This thread is about engine off P&G, I believe.