Bad Thermostat?

[Rusty1]

Was working on my truck today and got a few things squared away. Took it out for a drive and when I got home there was little bit of steam coming out from under the hood. The upper hose was hot,the radiator was hot but the lower radiator hose was cool to the touch. Bad Stat? Bad water pump? Clogged radiator? I'm hoping stat.

 

[89Suburban]

Where was the steam coming from? The overflow tank?

 

[Rusty1]

seemed to be from the cap. wasn't alot. I just let it run for about 10 to 15 min with the cap off. No flow. Just alot of burps. Air Lock?

 

[89Suburban]

Pull the thermostat and run it and see if it stays cool. If the system keeps filling with air it could be a bad head gasket or cracked head. Cheapest and first thing to check is the thermostat. That will also allow you to check for flow in the radiator with the t-stat pulled. Water pump going bad usually leaks out the pee hole. Never heard of an impeller falling off the shaft, not to say it doesn't happen, just unlikely IMO. I suppose you don't have a pressure tester?