temp. drops when i start to drive
 

I noticed today that my truck wasnt warming up as fast as it usually does and when i finally did it was when i was stopped, but as i started to drive again it would drop. out side temp 28* f hopefully someone could explain this to me or tell me if something is going wrong. Replace water pump, and t-stat 2 weeks ago.

my truck does the same thing it mostly because the water temp is so cold it takes a while to heat it up. when the thermostat opens it has all that cold water coming in making the engine cool back down.

i believe this is normal my truck will go to 200° then will go down

my truck would go all the way up to 210 but once it got their it dropped back down within 2 minites to 160 then started to go back up a new thermostat fixed the problem but then figured out the wire on the thermostat was corroded and not reading correctly