I have an Autometer Phantom electric oil pressure guage tapped into the head. When the car is cold it reads 50-75 PSI, but when the car warms up it will only read a max of 25 PSI as WOT. The sending unit is huge, and it will not fit behind the A/C Compressor. Are my readings so low because of it being in the head, or is my oil pressure really that low?