View Full Version : Oil Pressure readings erratic

08-10-2013, 12:24 AM
I've read on here a few threads about this topic, but I can't quite fit mine into any category and I've tried a few items to troubleshoot.

the boat: 2001 Prostar 209 Indmar Predator 310 HP

Problem: Oil pressure reading fluctuating during all operating conditions.

I know the problem is somewhere from the oil pressure sending unit, the MDC or the gauge itself. I'm hoping someone can shed some light into where the problem lies. Troubleshooting broken into potential problem area.

Oil pressure sending unit: Did the ground test for all analog oil pressure sending units. Gauge showed zero with open circuit, then showed max with attaching sending unit wire to ground. Leads me to believe its the sending unit.

MDC: When I first bought the boat, one speedometer was disconnected. Turned out to be for a good reason. It appears one of the baffles or something inside the MDC is ruptured as water got into the MDC from that pitot line. That caused erratic readings in the oil pressure, voltmeter and temperature gauge. Sometimes the gauges wouldn't register anything. Pulled that pitot back off, let it dry out, and now temp is solid, voltmeter is solid, but the oil still fluctuates inappropriately. ADDITIONALLY, on occasion I've had some of the gauges not register during a run. On the next "motor on" cycle said gauge reads the correct indication. All except the oil pressure, this one always seem to fluctuate.

Oil Pressure gauge: Now, I don't know if this is condoned or not, and I'm showing a little inexperience here... I swapped the oil pressure harness on the back of the gauge to the water temp gauge (I did this because all the gauges seem to be the same electric gauges with a different face... figuring all the real data is coming from the MDC). When I swapped in the oil pressure harness to the water temp gauge, the gauge went to the middle (about where it should be for warm oil), however it did not return to zero when I shut the motor down, so I'm not sure my similar gauge theory holds water. I then swapped the voltmeter harness to the oil pressure gauge, and the oil presure gauge showed the same erratic movement as if it still had the oil pressure harness attached like I was seeing earlier, which is the only reason I'm leaning towards the oil pressure gauge having problems.

Sorry for the long post, but I'm hoping someone can point me in the right direction. Thanks for looking.