Oil Pressure Sending Unit Wiring - Perkins 6.354

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TheLake

Veteran Member
Joined
Oct 16, 2021
Messages
56
Vessel Name
The Lake
Vessel Make
42' CHB Tricabin
Hi there.

I finally have my engine (at least one of them) back running (yay!!) after rewiring them. (Perkins 6.354)

Everything looks good, except I can't get a reading on the oil pressure gauge and am thinking I might have wired it up incorrectly.

Here are the symptoms and wiring:
- power on to panel and the needle goes full deflection to 80 psi (this is with nothing hooked up to it)
- I have 3 senders/switches. See diagrams. I believe that 3 is the sender.
- The other two I believe are oil temperature and oil pressure switches for the warning lights

So...my questions are:
1. am I correctly identifying the switches versus the sender? (and is there any clues as to which switch is for pressure and which is for temp?)
2. how do I figure out the wiring on the sender. I would have thought that it is like the other senders - each side goes directly to the gauge
3. how do I "troubleshoot" the sender. I thought I could put an ohmmeter on the terminals and that it would show a changing resistance as the pressure increases. But all I am getting is "infinity" for resistance


Thoughts?

Thanks,

Chris
 

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3 is the pressure sensor for the instrument. Perkins used lots of isolated ground systems on their engines. This sensor is an isolated ground type. A.C. Delco manufactured analog gauges that operated inverse to ground. When they were powered by battery but no sensor connected, they would swing full scale. If your gauge is not made by them, and no ground is connected to the s terminal, and the gauge goes full scale with key on, the gauge is faulty. Double check how it’s hooked up. If your engine is isolated ground you will have to connect the ground post to off engine battery ground. If the engine is grounded you can land one leg to a good place on the engine. I can’t tell enough about the other ones by these pictures. Alarms use on/off switches that are actuated by pressure or temperature. Pressure actuated will have a small port in their end where they screw into the engine. They are normally 1/8 inch pipe. Temperature switches have a bullet on their end that is wetted by the liquid it is monitoring. I think the items on your engine are switches as their bodies look large. I would simply unscrew them and identify their ends. Once out, you can clean them and likely identify their functions by the printing on their bodies. Sorry I could not be more help.
 
Thank you.

Yes, the VDO gauge does show full deflection when turned on. I will check my wiring to see if it's not correct to the sensor. The sensor has one line going back to the gauge and the other post goes to the common ground.

Thanks for the note about the switches and pulling them out to look. I have never done that...do I need to be worried about oil running out in a stream when I unscrew them out?

And, do I use a silicone tape on the treads when I put them back in?

Chris
 
Sorry for late reply. It’s been hectic. Remove the switches with engine cold and of course not running.
You may get a tiny trickle but not much more.
Thread tape can make its way into oil galleries.
Clean the threads with denatured alcohol or acetone or the like.
Get a bottle of permatex aviation gasket sealant.
Stuff works great.
Let me know how it goes.
God bless
 
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