lost oil pressure, engine shuts down, what next?

After running a few hours on and on, and after being shut down for an hour, the port engine on our 330 with 7.4's shutdown automatically due to loss of oil pressure. Good clean oil, no knocks, engine will restart and pressure comes up to normal on the dash gauge for about 3 seconds, drops to zero and then engine shuts off. Feels electrical to me, maybe a sending unit, sensor, or gauge. Was not able to check much last night. where should I start looking/troubleshooting?

Phil just my thoughts not an expert by any means. The odd thing is that you are linking the low oil pressure to some sort of safety shut down measure. I don't know if the 1997 carb 7.4L have such a thing. Now if you have the EFI engines that were optional then that might be true. Does seem electrical, like a sensor. As long as there is not oil in the bilge and plenty on the dipstick.....

These are EFIs and do have a little oil in the bilge, not much but is recurring. Just bought the boat and no reports from previous owner.

Start your trouble shooting by pulling the oil filter, cut it open and inspect for foreign debris. If you not sure what your looking for, compare it to the good engines filter.

If all looks good, install a manual oil pressure gage and see what you've really got going on for pressure.

If the pressure is then determined to be ok, then move on to your prognosis of an electrical issue.

You don't want to start guessing and throwing parts at the problem. You do want to determine that the actual oil pressure is ok/not ok.

I'm also thinking it's electrical too by the suddenness of the pressure drop at the gage. Best of luck with it.

Usually, if you lose oil PSI (pressure), it is not going to get better then drop off again. One tale tell sign of low oil PSI is lifter chatter however you said the engine ran fine with no noise. If the sender is bad it will cause the engine to shut down on your particular boat.

As per BonBini's advise, screw a mechanical gage into the engine where the sender is. It's the best way to check oil PSI. If you have no PSI there then it's time to dig into the engine to find the cause.

The 'older' boats do have a safety switch - if the engine loses oil pressure it will shut the fuel pumps off to avoid engine damage or other mishaps. The switch is basically one which has 12v on one side when the key is on - the purple side will then have 12v for about 5 seconds at startup and then only when oil pressure is present. The fact you can restart shows it will handle that first 5 seconds or so since it is getting fuel. You can try to remove the switch and clean it thoroughly - along with checking the wire connections going to it. This is different than the actual oil pressure sending unit which feeds the pressure to your gauge.

I noticed something similar on one of my motors when I bought it. I changed the oil and added some Lucas and it seemed to sorta help. I would start it up and it would hover around 60 pounds. After cruising for a bit, it would drop to 10, even at higher RPMs. This worried me......

I bought a new oil pressure sending unit to replace the one currently installed. When I reached down to remove it, I noticed it was loose. I tightened it up and all was good. A typical sending unit uses the block where it is screwed into as the ground. It was not screwed in correctly so it had a bad ground. A lot of people will also use teflon tape when installing their sending units. This is a no-no. You need ethat metal-on-metal ground where it screws into the block.

I would check your sending unit. maybe swap it with the other from the other motor.

The sensor that is connected to your engine alarm system though is a different unit. You actually have 2 water temp and 2 oil pressure sesnors on each motor. One is for the gauge, and the other is for the alarm (it's a simple on/off idiot light type sesnor).

Check them both..... You say you have a little oil in the bilge? Check to ensure your sensors are tight and/or installed correctly...

As far as multiple sensors/senders for the oil pressure monitoring system... Phil Schmidt comments a sudden lose of "op" followed by engine shut down. Highly unlikely repeated, simultaneously, multiple sensor/sender failure. If electrical, I would suspect something that the sensor/sender are in common with.

These symptoms have "intermittent electrical" written all over them. Lets just hope he's not making metal internally and intermittently plugging the engines sensors/senders.

The more I think about it the more I suspect water in fuel.