my 07 ford F-150 has been having some issues. when i first start up my truck the engine temperature seems fine but within ten seconds it drops to zero . the check engine light has come on and when i give the truck plenty of gas the temperature rises back to the center position . then when i let off completely it drops back down.. mechanic says it might be the sensor but i needed a second opinion.

 

Sounds like you are low on coolant. Honestly if the sensor was bad i would think it would read bad all the time not just when you get off the gas.
What were the codes the check engine light have you?
Might also possibly be a stuck open t- Stat

 

You should have a code if the check engine light came on.

 

P1288 is the code I believe it's throwing

 

Yep, that's a bad CHT sensor.