TMD 40 Oil pressure instrument fault

[Leighb]

On my Stb engine when I switched on yesterday there was no alarm sound and the Oil pressure needle jumped up to about 50psi, Fuel gauge and Temp gauge behaved normally. The Port instruments all as normal. The boat has only just been relaunched, but was running normally when serviced in November.
I did not try and start it, as wanted some advice as to the likely cause of this issue.
TIA

 

[vas]

broken/rusty/bad contact cable off the sender (most likely) or at the back of the gauge (not sure alarm wouldn't sound though)

 

[dragoon]

The oil pressure switch (alarm) and sender (pressure gauge) are units with 2 connections, that are earthed to the engine one one side of the circuit. On my 40's they connect via a crimped terminal onto a bolt on the bottom of the oil cooler. I expect this connection has failed / is failing, taking both systems with it. You've probably discovered already, it's quite a pain to see anything down there as it's all under the heat exchanger. If you locate those 2 wires that go to earth and make up a new connection to an earth point on the engine (maybe a bolt mounting the strainer or similar) it should return to normal.

 

[Leighb]

The oil pressure switch (alarm) and sender (pressure gauge) are units with 2 connections, that are earthed to the engine one one side of the circuit. On my 40's they connect via a crimped terminal onto a bolt on the bottom of the oil cooler. I expect this connection has failed / is failing, taking both systems with it. You've probably discovered already, it's quite a pain to see anything down there as it's all under the heat exchanger. If you locate those 2 wires that go to earth and make up a new connection to an earth point on the engine (maybe a bolt mounting the strainer or similar) it should return to normal.

Thanks, that is helpful, it would be the starboard engine!!! I can/could just about get to the oil pressure sender on the Port engine a couple of years ago, but that was before my left wrist seized up with OA, right one already surgically fused. It will be someone else who has to do the grovelling. Hopefully they can sort it. I am reluctant to run it without any oil pressure info.

 

[dragoon]

Thanks, that is helpful, it would be the starboard engine!!! I can/could just about get to the oil pressure sender on the Port engine a couple of years ago, but that was before my left wrist seized up with OA, right one already surgically fused. It will be someone else who has to do the grovelling. Hopefully they can sort it. I am reluctant to run it without any oil pressure info.

I think you’re sensible there. My port oil cooler developed a leak recently and I only noticed because of the pressure dropping on the gauges.

 

[Leighb]

Update, the yard have spent some time tracing the fault. Decided it was a faulty sender and have replaced that and checked the wiring. Now on switch on the alarm sounds and the OP gauge flickers and reads zero, so that’s OK, but once started the gauge goes up to maximum pressure, once warmed up and throttled back to idle rpm it reduces a bit to around 90 psi. Before this the running pressure was about 60 - 70 psi reducing to around 45 at idle.
Does this perhaps suggest that the replacement sender is not right for the gauge? At least I do have some indication that there is oil pressure in the engine. ?

 

[vas]

most likely... iirc output range is same, no matter if it's a 0-5bar or 0-8 or 0-10...
if you have the old one, it should say what it is on the hex just above the threads, carefully clean all old pain and muck first.

ps I'm talking vdo senders here, not familiar with other brands and markings