[yotatechie04]

Again, I have to say that I agree with Joe, most likely it's going to be the coolant, but in some cases, if you have low coolant and your heater core goes bad, you won't have any heat, and there won't be any tell tale signs of a bad core, usually when you have bad core, you'll have coolant leaking in the floorboards of the car, but if you're coolant's down way too far, you won't have that. Check all of those though, could be either or. Best of luck to you!