So I bought this thing used at at 92K miles... it now has 93.5K and I've had many overheating issues. First though was thermostat replaced, rad cap replaced, fan switch replaced, flushed the radiator, then I was befundled when none of this fixed it. I was thinking a cracked head because the knock sensor had been comming on, I was really scared. Took it to a mechanic and there's no carbon in the coolant. He then proceeded to tell me that this car should have a coolant reservoir and that I'm losing coolant out of the overflow when I accelerate and go up hills because of this. So my question is, should this car have one?? If so, who the hell would modify this and take it out???????? and why?