Oil pressure problem or just the gauge?

Chip S said:
Using jumper wires to switch the gauges would work. Since the gauge went to 80 psi when you grounded the sender wire the gauge is most likely working correctly. Corrosion on the sender terminal could affect the reading but if its still reading 20 psi after cleaning the terminals I'm guessing the problem is not the gauge.
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Correct. Senders do go bad. Corrosion on sender terminals will create problems.

Shark has 5.0's, and just a quick google search had this:

Mercruiser 5.0L Marine Engine Specifications
Models 5.0L 5.0L EFI
Maximum rpm @ WOT3 4400-4800 rpm
Idle rpm in NEUTRAL3 650 rpm5 600 rpm6
Oil Pressure @ 2000 rpm 30-60 psi (207-414 kPa)
Min. Oil Pressure @ Idle 4 psi (28 kPa)
 
scoflaw said:
You might want to see if you actually do have oil pressure while you fiddle about.
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Yes, understood. I’m just trying everything that’s easier first. I can barely reach the sender to clean the connection, so I’m not sure if I can remove it, and replace it with a mechanical oil pressure gauge. I’ll be back tomorrow to give it a try. If I can get it out, I’ll go buy a gauge and test it.
 
CaptRonn said:
Correct. Senders do go bad. Corrosion on sender terminals will create problems.

Shark has 5.0's, and just a quick google search had this:

Mercruiser 5.0L Marine Engine Specifications
Models 5.0L 5.0L EFI
Maximum rpm @ WOT3 4400-4800 rpm
Idle rpm in NEUTRAL3 650 rpm5 600 rpm6
Oil Pressure @ 2000 rpm 30-60 psi (207-414 kPa)
Min. Oil Pressure @ Idle 4 psi (28 kPa)
Click to expand...
Thanks Ron, last time out, the gauge was at 0. Today I pulled the connector boot off the sender and brushed the sender terminal with a wire brush. Started the engines and starboard gauge says 20psi (port engine around 30). Maybe 20 is fine since it’s at idle. Tomorrow I can take it for a short test drive and see what it reads at higher rpm’s. Appreciate all the advice and the google search!
 
Simple easy way to test pressure is to tap in where the ecm oil switch is at the top of the motor near the distributor. Use an 1/8" npt nipple about 4" long.
 
scoflaw said:
Simple easy way to test pressure is to tap in where the ecm oil switch is at the top of the motor near the distributor. Use an 1/8" npt nipple about 4" long.
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I didn’t know about that switch. I’ll look for it today. Thanks for the tip!
 
If you need to replace the gauge be sure to tell supplier you have twin engines. I replace a gauge once and the reading was very low. Took it back and dealer said you need a different gauge when you have twin engines. New gauge worked will and oil pressure was correct.
 
Shark said:
Do you think it’s worth paying $69 for Quicksilver Mercury OEM sender vs. $29 for Sierra aftermarket sender?
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My guess is they are both made by the same people. I went to NAPA to get new ones for our Detroit engines, problem fixed, no issues since, ( 4 or more years ago )
 
Shark said:
Do you think it’s worth paying $69 for Quicksilver Mercury OEM sender vs. $29 for Sierra aftermarket sender?
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Make sure the sender matches the gauge. Sea Ray used a variety of gauge manufacturers, and not all gauges work on all senders. Do some homework to make sure you are ordering the correct one.

To answer your question, if the Sierra is the correct model, I would use that.
 
At idle, the gauges are showing 20 psi on one engine and 30 on the other. If I want to see the readings at 2000 rpm, can I use the “throttle only” button on the shifter, to rev the engine, in the slip? Or should I take the boat out to get it up to the higher rpm?
 
The throttle only buttons felt a little sticky, so we just took the boat out for a quick test spin.

Gauge stayed at 20 psi from starting through 3800 rpm (port went from 30 to 40), which is where the starboard engine maxed out for some reason (happened once before with a bunch of people on board, and never again until today).

On the way back, after maybe 10 mins at 3800rpm, gauge dropped to slightly under 20 psi, and when I throttled down for the canal, it dropped to 0, and stayed there.

Docked the boat, and opened the hatch with engines running - no knocking or lifter tapping noises, smoke, or anything else abnormal. Very weird. Going to see if I can get the sender out.
 
Shark said:
The throttle only buttons felt a little sticky, so we just took the boat out for a quick test spin.

Gauge stayed at 20 psi from starting through 3800 rpm (port went from 30 to 40), which is where the starboard engine maxed out for some reason (happened once before with a bunch of people on board, and never again until today).

On the way back, after maybe 10 mins at 3800rpm, gauge dropped to slightly under 20 psi, and when I throttled down for the canal, it dropped to 0, and stayed there.

Docked the boat, and opened the hatch with engines running - no knocking or lifter tapping noises, smoke, or anything else abnormal. Very weird. Going to see if I can get the sender out.
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Re-started the engines after about 10 mins, and gauge never moved from 0.
 
I would swap the sensor from the port to the starboard Engine and see if the problem follows or not. It seems like the guage worked by grounding it....
 
Chris-380 said:
I would swap the sensor from the port to the starboard Engine and see if the problem follows or not. It seems like the guage worked by grounding it....
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Yes, thanks for the idea. I swapped the gauges with a jumper wire and the gauges were consistent. Thinking it’s the starboard sender. The port sender seems almost impossible to get to. I was thinking about just trying a new sender on the starboard engine.
 
Shark said:
Yes, thanks for the idea. I swapped the gauges with a jumper wire and the gauges were consistent. Thinking it’s the starboard sender. The port sender seems almost impossible to get to. I was thinking about just trying a new sender on the starboard engine.
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That would def work, I added fox marines to my 380, which added an oil sensor in parallel to the stock one. Since my engines are reversed, the starboard was a pita, did it by feel... port was simple....

good luck, seems like you are close to the answer
 
Chris-380 said:
That would def work, I added fox marines to my 380, which added an oil sensor in parallel to the stock one. Since my engines are reversed, the starboard was a pita, did it by feel... port was simple....

good luck, seems like you are close to the answer
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I don’t know much about fox marines, but if those are the digital gauges, I would love to have those. Yes I think I’m getting close. Thanks again for the feedback!
 
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