Oil pressure guage

[Tikvah]

It's been an interesting start, but we're making miles just the same.

After the first hour of driving the oil pressure gauge went from a healthy 50+ lbs to a fluttering needle around 0.  Then after a few miles simply went dead.   Immediately I stopped and checked oil level and the engine oil gauge and all is good.  So, with the confidence of historical good pressure, I continued down the road.

However, what caused my dash gauge to die?  Where does the wire come from?  There seems to be some kind of sending unit on the manifold where the engine-mounted gauge sits.  Is that my oil sending unit?  Would that automatically be the problem?

[bevans6]

On my MCI that little manifold has two electrical sending units.  One is the oil pressure sender, one is the low oil pressure switch.

Brian

[Oonrahnjay]

On my MCI that little manifold has two electrical sending units.  One is the oil pressure sender, one is the low oil pressure switch.    Brian 

     Out of curiosity, Brian (my bus has a temp engine shutdown but not a low-oil-pressure auto shutdown), is the low oil pressure switch on your bus only a warning system for the driver, or does it trigger an automatic shutdown?

      Thanks,  BH,   NC    USA

[bevans6]

Now, it's disconnected  

Before, it triggered an alarm buzzer and a warning light, and if the engine stop relay option had been added it would also shut down the engine.  I never looked to see if I had the optional engine stop relay.  This relay would be what supplies power to the engine stop skinner valve, which allows the engine to run if there is power to the skinner control terminal.  No power, engine shut down air cylinder gets air and the engine stops.  The hot coolant temp sensors (two of them, one on each thermostat housing) would have also triggered the alarm buzzer, their own light, and controlled the engine stop relay.  If you want to add one you should be able to, just wire it in parallel with your hot engine sensor(s) and it is a 3 psi switch.  

As an aside, the starter switch is hooked into the engine stop relay to over-ride it while the engine is cranking.  Engine cranks, starts, gets oil pressure, engine runs.  If you try to start the engine with no oil, it will crank and try to start but will stop as soon as you let go of the switch.  Same if the engine is too hot and you try to re-start it.  The sensors are switched to ground, and supply a ground to the control coil of the relay to cause the relay to open, and interrupt power to the skinner valve.

Brian

[Oonrahnjay]

Now, it's disconnected   ....

If you want to add one you should be able to, just wire it in parallel with your hot engine sensor(s) and it is a 3 psi switch.  ...

Brian   

      Thanks for that info.  I suspected that that was the way that N American engines worked.  My shutdown works through a solenoid-type engine cutoff unit that pulls a rod on the fuel pump.  Would be easy to adapt a low oil pressure switch to that circuit too, but I'm in the middle of an engine change and the current engine will be going away soon.

      But just for general knowledge, it's good to know how it works.   Thanks,  BH

[Ed Hackenbruch]

Dave, my oil pressure sending unit died while sitting in the shop during the engine rebuild.....  Put a new one on the manifold and back in business.

[Tikvah]

Is it the silver one with the single wire or the black/blue one with the two wires?
Is it locally available or is it a DD part?

[Ed Hackenbruch]

Don't have one like the blue/black one on mine. Both are only single wire like your silver one.  It is a Stewart Warner #279A  I think that the shop got it from Napa but not sure about that.

[luvrbus]

The sliver one wire is for the gauge the 2 wire sensor is the low oil pressure shutdown and light

[Tikvah]

Thanks, I'll try to pick one up tomorrow and I'll report back on the success.