My temp gauge is really irratic. Usually when im driving and under a bit of load it reads but sometimes in the higher gears at low rpm it doesn't read at all. It's a really weird problem. Also could this be causing my terrible gas mielage since driving a colder car consumes more fuel.

 

id say bad thermostat,
which causes it to use more fuel b/c engine temps r not staying at normal temp..

replace it .......with a oem one.