Greetings,

FYI, temperature extremes shouldn't affect the function of a standard dry
chemical type fire extinguisher that many people keep in thier cars.  Dry
chem extinguishers contain the chemical in the form of an ultra-fine powder
and are pressurized with dry air or nitrogen.  The only things that can go
wrong are not temperature dependent but include compacting of the powder if
stored in one position for too long, a leaky seal that allows the stored
pressure to bleed off, or a malfunctioning valve.  It is recommended that
you have extinguishers inspected annually, but if you don't (honestly, who
does?) then simply invert your extinguisher at least once a year and give it
a few whacks with a rubber mallet to break up and shift the powder inside it
before storing it again in it's holder or bracket.

For a typical car type fire involving the engine compartment, it is my
preference to use a CO2 extinguisher.  The fine powder in a dry chem
extinguisher does an admirable job of putting out the fire, but the powder
literally gets everywhere in every nook and cranny and can be corrosive.
CO2 may take a little more effort to put out the fire (it works best in
enclosed spaces) but if you are planning on ever rebuilding the motor after
the fire it won't leave any residue or cause any damage.

Cheers - Jonathan

Never really see a difference in the "charge" gauge on mine, even in sub
zero temps.

The temperature won't affect the extinguisher operation, it MAY affect
the valve if it is one of the cheap plastic ones, it may get brittle and
break when you try to use it. If it is a good unit (Kidde, Sentry, Ansul
etc.) it won't have a problem. One thing that should be done is to
inspect and shake the unit at least once a year to keep the powder from
caking in the bottom and to check for leaks.

Steve W.