I have twin 5.7 mercruser engines. The port side reads about 70 at idle and pegs at WOT. The starboard reads very low at idle abot 10 I guess and goes to about 70 or 80 at WOT Is this ok? Can someone please explain to me how oil pressure works.
The sender has a diaphragm pressing against a spring, and also moves a wiper connection on a resistor. As pressure increases, it presses against the spring, compressing it and moving the resistor wiper. That allows more battery current to appear at the gauge. The gauge is really a DC voltmeter, with the scale graduated in PSI.
I expect the one that reads 70 psi at idle is the defective sender, but you can check them with a voltmeter and compare.
you could also swap the leads on the meters and see what happens to the readings. I suspect the meters or sending units are at fault. but a mechanical pressure gauge is what you really need to find out what the true pressure is..
i agree with flashback.Two months ago they were jelous of me having 60-70psi until i changed the intake manifold gasket and made a damage to the pressure sender.With the new one the pressure was the half.After geting some advise from the experts i attached a mechanical pressure gauge to the hole of the sender and i confirmed that the pressure was really the half!
When mine is cold, I have 30ish psi at fast idle (per electric gauge and mech gauge by engine) When I accelerate even little, it goes to 40~50. After its nice and warm and you decelerate real fast, the pressure can drop to 15) but if you accelerate to 900~ 1000 rpms, its back up to 30~40. GM says all you need is 7 at idle.
