What would cause my 2000 Mazda B2500 to run cold?

Hi I have a 2000 Mazda B2500 that is running cold. It has the 2.3 engine. I just replaced the thermostat and there is no signs of my head gasket being bad. Does anyone know what could still cause my truck to run cold?|||If you think the car runs cold because the dashboard gauge says so, you might actually just have a bad connection or a bad gauge. But I'd also start with the thermostat once you know the car is indeed running cold.|||How do you know it's running cold? The only thing I can think of is did you check the radiator "fan clutch" ? Have you got plenty of antifreeze in it? Get back to me with these answers. we'll go from there.|||you may have gotten a bad thermostat I have had the same thing happen before and I got another new thermostat and it fixed the problem.