Detroit Diesel oil pressure alarm

[brico]

Just recently my 1980 DD 6-71 NA engine oil pressure alarm/gauge started playing games with me. When I turn on the ignition key on the Port engine i do not hear the alarm but when I start the engine and run it for a while oil pressure reading is 40 PSI. When i stop the engine the alarm beeps as expected and the gauge reading goes to zero. When i turn off the ignition key the gauge reading goes to 10 PSI??When I turn it on again, the pressure reading goes to zero and alarm beeps.

On the Starboard engine when i turn on the ignition key i do not hear the alarm. When I start the engine and run it for a while oil pressure reading is 40 PSI. When i stop the engine the gauge reading goes to zero but no alarm beeps. When i turn off the ignition key the gauge reading goes to 20PSI??? When I again turn on the ignition key, pressure reading goes to zero but no alarm is heard at all.

How do I troubleshoot this problem?

[spartonboat1]

Please indicate rpm's and water temps associated with pressure readings. If 1,1-1,400 rpm, then pressure should be 50+ or so, as that is the point at which the pressure relief valve lift off pressure; esp. cold.

If warmed up to around 170 degs, idle pressure (650 rpm) could be 15-25 #'s. When raising rpm, pressure should rise, go above 50 #'s, then at about 55 #'s, drop back to 50 and hold steady, as the relief valve lifts off.

If engine turned off, pressure should drift to zero. When key is off, engine off, I would expect to see 0 #'s, until started. I have direct acting pressure guage, but maybe you have electric over hydraulic, as I don't know you vintage boat. I have a 1972 43' with 6-71 N's (not NA's).

[brico]

Thanks for quick response. The RPM is at idle 5-600. Manual says 30-6-0 PSI at that RPM is expected pressure. I am not concerned about the actual pressure reading as it seems the pressure gauge is showing correct and expected pressure reading when engines are on. My concern is the lack of audible alarm especially on Starboard engine should the engine oil pressure drop for whatever reason I would not get the audible alarm and I am not looking at the pressure gauge at all times.

[workingonadream]

check the fuse for the alarm. mine has its own fuse insert for the alarm. start there first, and then move along if the fuse is good. you can put power directly to the alarm to see if it sounds to eliminate a bad alarm, don't juice it up for too long, I would just do a quick tap to see if there is sound. as for why the gauges read above zero when the key is off may be a grounding problem, I had a similar problem with my car years ago and it was a broken ground wire. all I can recommend is that you check and clean all connections, and go from there. good luck