Engine Oil Pressure Gauges

[brico]

Recently I replaced engine oil pressure senders and gauges as old ones were not reliable and couple of gauges were broken.With new senders and gauges when the engine is started at say 1000 rpm to warm up or when hot and running at >1800 RPM the gauges are showing correct pressure, but if I reduce RPM below 1800 or when idle approaching slip in the marina, the pressure gauges drop to practically zero. What could be the reason for this? The senders are positively for dual gauges.

 

[Bob Bradley]

That may be a symptom of bearing wear. Before I got too concerned, I'd install a pair of mechanical gauges at the engines and have someone observe them under the conditions you describe.

 

[Fanfare]

I run straight 40 weight oil in my engines and generator. With both my old 8V-71Ns and newer 6V-92TAs I get higher oil pressures on cold startup. However, after a day of running, when I come into a slip at idle, the pressure drops down to perhaps 6 to 10 psi on the gauges. On my old 8-71s this would often sound the low oil pressure alarm, generally just for a second after pulling the throttles back. The straight weight oil becomes much more fluid at higher temperatures and can pass through various apertures such as sensors more rapidly. Last time I checked Detroit Diesel forbids multi weight oils for these diesels.

It is certainly possible that you could have some problem but you probably do not. I have put in mechanical oil pressure, fuel pump pressure and engine temperature gauges in each engine room. A hand infra red thermal gun is also pretty neat to use on several spots on these engines.

 

[racclarkson@gmail.com]

Recently I replaced engine oil pressure senders and gauges as old ones were not reliable and couple of gauges were broken.With new senders and gauges when the engine is started at say 1000 rpm to warm up or when hot and running at >1800 RPM the gauges are showing correct pressure, but if I reduce RPM below 1800 or when idle approaching slip in the marina, the pressure gauges drop to practically zero. What could be the reason for this? The senders are positively for dual gauges.

Do your OP alarms work? What what volt is the boat?

 

[brico]

Thanks Guys. I do have mechanical gauges and they are showing about 15PSI at 1250 RPM when engine is hot, and almost identical pressure at startup and at higher RPM so pressure is there. The alarms work well. I've changed the OP alarms couple of years ago when one failed. It is just unnerving to watch the low/zero pressure on the gauges at lower RPM and at idle when I am approaching the slip but knowing that it is higher. The voltage is 12V. I guess I will have to check the ground wires again.

 

[luckydave215]

15 PSi @1250 rpm (if it's real) sounds low, I see closer to 30, 40 at cruise.
3-5 psi idling hot isn't unusual, many DDs will ring the bell when going into reverse with forward way on.