The temperature has dropped quite a bit around here this past week so the heater has been on a lot, but I've noticed it only seems to get warm, not at all hot like it used to.

The valve is working, I can switch it from warm to icy with no problems. I don't think there is any problem with the core, no leaks and both hoses heat up just fine (in and out of the core). I noticed today on the highway that it seems to be a little cooler at highway speeds, but not a large change. This makes me suspect the thermostat, however the temp gauge never wavers (which I realize doesn't say much) but also I checked it the other day, started the truck cold, let it warm up. The top radiator hose stayed cold until the engine hit operating temp then heated up quickly. There are no bubbling sounds, coolant is full.

I'll probably put in a new OEM double hole thermostat anyway, no idea how old the current on is anyway. Any other ideas though? Preferably an ingeniously simple solution I've overlooked that doesn't involve me being mechanic outside in below zero weather. <img src="/forums/images/graemlins/smile.gif" alt="" />