I have a west facing double garage door that is absorbing and radiating heat in the afternoon into the garage space. The temp difference between inside and outside of the garage is horrible.

A petrol can left on the garage floor exploded yesterday afternoon, due to the expanding gas.
When I got into the car it shows outside temp was 44 degree, driven out of the garage for a few minutes and it drops straight back to 32.

does anyone know of garage door insulation kit easily available from bunnings?

one thing you can do is put a vent into your roof and then have a couple of whirly birds.
My garage is now at a closer temp to the outside temp.

roller door, panel lift or tilt lift?

roller door

speaking of vent i don't understand the logic behind venting cooking smell into roof space, any builder still doing that should have their head check by a butt specialist.

Thats why its against the BCA. Shold always be vented to atmosphere.

I think something similar to
Owens Corning Garage Door Insulation Kit
might do...

Looks to be more for winter heat loss...no sure how well it would prevent radiant heat, there would be no air gap.

Personally, I would never keep petrol or any type of flammable liquid like that in my garage.

Jerry cans and similar containers are not vented like car fuel tanks and so the do build up pressure and can be dangerous.

The other thing is that in high temps the fuel vapors are more volatile and can ignite by a smaller spark source.

Putting a vent in the ceiling and using whirlybirds will help reduce the heat but the petrol can will still expand and contract with heat.

This might be a noobish question guys, so please don't flame me:
It does make sense if the outside temp is cold and you wanted to keep the inside warm.
But insulating the garage door panels wouldn't it make it worst after you've driven and parked your car? wouldn't it slow down the heat dissipation time?

yes it would, but wouldn't really be an issue i would think.