My toyota pickup won't stay warm. It will idle until warm but then when you start driving the temp drops to below the cold line. Any ideas?

If it's cold outside where you live, try covering the radiator with a piece of cardboard (winter front, as used in AK). Also, try replacing the thermostat with a new OEM product--it may be opening too soon.

A gasoline engine should NEVER need cardboard in front of the radiator. It didn't come from the factory that way and the radiator didn't get more efficient as it aged. The thermostat is almost always the cause of an engine that can't maintain proper temp. TXGrease is right on when he says get factory T-stat. Or buy STANT. Other brands are junk.

Also, I should have mentioned to purge all air in the cooling system.