have a 1998 murcury 40 hp ELPTO SERIAL #OG616340 it has a water pressure gauge that shows less then 5psi at idle. when the rpms increase to 2000-2500 the water pressure increase to 20 or so. should the water pressure flactuate that much? bad water pump/impellor? same pontoon and engine shifts into and out of gear hard, is there an adjustmentor libe point on the shift linkage?
