i found 6 year old batteries in my car are they still good?

they might have some capacity left in them but it is doubtful. cold rarely damages dry cell batteries. all batteries have self-discharge, so the storage life depends on how much of the original charge is lost while sitting. a car interior gets hot enough to accelerate this internal reaction and shorten the battery life.

Just use them. If they are dead, throw them out. I doubt they are. Also don't just throw them in the garbage. They must go in recycling . Batteries contain extremely toxic stuff. We don't want them in the landfill contaminating ground water.

test them with a volt ohm meter and you'll know. an auto parts store can test them or radioshack

I would say just try them out:)