i would say its normal mate, ive seen a few of these read very low when they get to operating temp. mine used to fluxuate up and down all the time, very unreliable. if you wanted to be certain then get your hands on a known good test gauge, pull out the o/p switch and screw the line in and jus feed line through your window go for a drive and watch the gauge, only way to be sure, cheers.