Okay, we've said that an extinguisher rated for car-likely fires is good. But what exactly is the kind of extinguisher/rating for these situations? No one has said. I am all ears... or eyes, whatever.

Well there is a difference between rated for car fires and rated for car fires and won't harm the electronics... which do you want to know about?

I'll pipe in ... how about all the above (I know nothing about car extinguishers).

Same here. School us.

Since other more reliable and knowledgeable sources seem reluctant to respond, I'll take a shot at it.

As related above, I use halon or clean agent halon which is what replaced halon after it was discovered that halon apparently causes ozone depletion. Halon is the same gas used to protect computer rooms. The benefit of halon is that it does not leave behind a caustic residue like dry powder extinguishers which will cause havoc to a car interior. The lack of powder residue is helpful if dealing with a small fire. The halon extinguisher is bolted to the front of the drivers seat where I can reach it while belted in the seat.

That said, I keep a standard 5lb ABC dry powder extinguisher in the trunk as well as a back up. I like the knock down power of the ABC, but there will be a substantial mess to clean up.

I believe the the best compromise between halon and dry chemical is CO2 which is what sits in my garage. Unfortunately, the CO2 extinguishers need to be rather large to be effective and are thus not favored for in-car installation.

YMMV.

Craig.

I carry a 5lb ABC in my vehicle. When I was with the fire company I carried a 20 LB ABC. They make a huge mess. They work well on a lot of things.

I used to have some CO2 extinguishers. They were always empty after the kids discovered that they made dry ice.

Here is my uneducated thinking about car fires.

One question is if the extinguisher is going to be reachable if the car is burning. If reaching the extinguisher places you at risk of getting burned it is not worth fighting the fire. Sorry but true. If the the car is already burning then an extinguisher inside it is a hazard rather than a help, especially if reaching it places you in harms way. Not only does trying to get it place you at risk from the fire, the pressurized extinguishers are potential bombs.

I think the biggest fire hazard in a car is battery driven electrical and fuel fires, mostly from under the hood. In an accident wires are often shorted together from the impact and making sparks, sometimes even just heating to the flash point temperature without sparking. Disconnecting the battery can remove that source of ignition.

If you are early enough to be concerned about the condition of the upholstery in a car you should be able to extinguish the fire with your bottle of drinking water.
If it is past that time then you are already past being worried about how much of a mess the extinguisher makes, and are likely past the insurance company's write off point for damages to the car.

If there is a fuel tank rupture you are looking at a large amount of fuel and again the mess from the chemicals are not going to be much of a concern.
In the case of a fuel tank starting to burn I would be more concerned about making sure everybody was clear of it, not because I expect it to explode like in the movies, but because leaking fuel spreads and burns fast with a lot of heat. Ten gallons of gasoline running all over the road and flaming is definitely a job for professional firefighters and certainly not a job for panicked accident victims with a small extinguisher.
Safety first, get the people clear of a fire hazard then fight it if it makes sense, but do the first aid for the victims before worrying about saving the vehicle. It is better to let the vehicle burn and save a life instead if you need to choose.

...Now there are other reasons to have a small extinguisher handy in your car. It might be somebody else's car on fire, or the fire might not be a car at all.
So I think yes for a small extinguisher, but with some cautions.
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Does that about sum it up?

I keep a Kidde 2.5-pound automotive extinguisher strapped to my rollcage in the Jeep, right behind the driver's seat. Easy access, even when rolled over and belted in. I've seen too many offroad rigs get burned to the ground.

Don't bother with the car in a car fire - protect exposures (houses and such) you can't really save a car that has fully ignited. If you can put it out in the first few SECONDS of fire, you might save it. Once the fire is in the passenger compartment - it's over.

Have to second this one.

Unless it might be a collectable, or have a loan against it and you forgot to pay the insurance bill this month LET IT GO.

There is not much worse than a car that has been repaired after a fire or flood. Well, except the burn ward.