I've replaced the thermostat and I'm still getting no hot water in the lower radiator hose. I don't overheat until I'm driving a little bit and then slow down. I used to be able to turn on the heater to alleviate the problem, but now I get zero response from that. It feels like regular air is coming out. Any ideas? I'm beginning to think it may be a radiator flow problem, but I'm not too sure. Please help!