Mercruiser Oil Gauge pegged KOEO

[komodo_goods]

Hello,
I have been troubleshooting the oil gauge (P/N 73180), which is pegged at 80 psi, and am at my limit for troubleshooting, so I need assistance from the forum if anyone could. Below is what I have done to T/S thus far to troubleshoot.

1. This is the original condition when I bought the boat in July 2023. This is a 1998 Chapparal 232 with a Mercruiser MCM 5.7 2bbl. The gauge returns to ZERO with ignition off.
2. KOEO or engine running the oil gauge is pegged; a new sending unit was installed before I purchased it in July.
3. Removed the signal wire on the sender and jumped a good wire to signal on the gauge and the condition remains while installed on the boat.
4. Removed gauge from boat and bench tested with the oil sender (verified it is at 250ohm) and it still pegs at 80psi.
5. I ordered 3 different oil senders (2 cheap, 1 OEM) 250 Ohm senders, and the condition still exists while bench testing.
6. When air pressure is applied to the oil sender while being bench tested, the gauge responds and moves just a bit past 80psi.

I'm leaning toward the two solutions below.
1. Order a replacement (used) gauge (P/N 73180). I have done this tonight and will receive it next week.
2. Somehow this American-made 1998 boat has a European gauge/sender in it and needs the associated sender to work correctly with the gauge, which I cannot seem to find a part number for.

Is there anything else I'm missing that I need to troubleshoot?

Thank you in advance for any help or suggestions, as I'm at a loss on this one.

 

[alldodge]

The gauge pegs if its on the bench or in the boat. This says the gauge is the problem

North American standard is 240 ohms (cold/low) to 30 ohms (hot/high)
So when the sender wire is grounded the meter will peg. The European standard is reversed, so when wire is grounded it will go low/cold.

 

[QBhoy]

I think you maybe have a mix match between the gauge and sender

 

[komodo_goods]

QBhoy,
thanks if the replacement gauge does not work ill buy a euro sender. do you by chance know the P/N?

 

[stresspoint]

i usually try to replace both the sender and gauge together.
unless i am going OEM on either,
this method i have found over the years to be the best option because the gauges from different china manufactures are never or" very rarely "the same match to the sender or visa versa.

one thing i used to do on HP street cars was use a capillary gauge so i was always getting a true oil pressure reading, this can be done on a boat but the oil line routing is a PIA . some guys with HP boats T into the fitting and mount a gauge to the motor where it can be seen while cover is off when tuning..

 

[komodo_goods]

All,
I'm happy to report that the new gauge arrived and corrected the problem. It must have been an internal short in the old gauge.

Thanks for the help.
Komodo