Looks pretty good! And I don't think they need much else. CR 10 may be fair, though the hp are a bit low for it, aren't they?
I'd say Challenge Rating 9. They don't have an Iron Golem's multiple attacks and poison breath.
Healed by Flames looks good. We could make the temp hp cap scale with size - maybe equal to the golem's Construct bonus hps?
Healed by Flames (Ex): An attack that deals fire damage breaks any slow effect on the firedog and heals 1 point of damage for each 3 points of damage the attack would otherwise deal. If the amount of healing would cause the golem to exceed its full normal hit points, it gains any excess as temporary hit points (to a maximum equal to a Construct's bonus hit points, 20 temporary hit points for a Medium-sized firedog). For example, a firedog hit by a fireball gains back 6 hit points if the damage total is 18 points. The firedog gets no saving throw against fire effects.
Regardless, Healed by Flames needs to be added to Special Qualities where the "fire resistance 15 or immunity to fire" is.
Apart from that it's just construction. We can use the Iron Golem's with something fire-related instead of
cloudkill (how about
fire shield for the sake of argument) and lower weights and gp values.
Price 50,000 or 60,000 gp? It's somewhere between a Clay and Stone Golem in nastiness.
How about this for a start:
Construction
A firedog’s body is sculpted from 600 pounds of pure iron, smelted with rare tinctures and admixtures costing at least 1,000 gp. Assembling the body requires a DC 16 Craft (armorsmithing) check or a DC 16 Craft (weaponsmithing) check.
CL 14th; Craft Construct,
fire shield,
geas/quest,
limited wish, caster must be at least 14th level; Price 150,000 gp; Cost 80,000 gp + 5,600 XP.