No, no heat gain from what I can tell. I am really looney about things messing up my truck, so I check under the hood almost every time I get out of the truck after driving at night. Just to make sure there is no problem with the lights. Once my obsessive compulsion wears off, I will stop doing that. I got the 6000k kit based on the recommendation of the people that HID'd their Lexus GX's. As far as the light output goes, there is so much light on the 6000k kit, I think the 4300k kit would be too much for oncoming and drivers in front of you. In fact, I am going to adjust my 6000k's to aim downward a bit because I feel bad for those in front of me in small passenger cars.