Low Oil Light

[Lin]

We just went out with the family into the National Park.  The bus seemed to behave beautifully.  The highest temp was about 190 while climbing a couple of thousand feet.  Otherwise it stayed around 170.  This would be a trial run to make sure all is okay if we are to take our trip up north.  Just as we returned home though, the Low Oil light began blinking.  The gauge, although fluttering is reading 40 psi at 800 rpm and over 60 psi at 1800 rpm,  The light keeps blinking though.  Any ideas where to look first?

[desi arnaz]

look first on your dipstick to see if you have any oil........

[Lin]

It's about 1/2 gallon down.  If the oil pressure was actually low, wouldn't the gauge show it also?

[luvrbus]

Lin the sending unit provides a ground to make the light come on probably a wire grounding out some place in the circuit,or your sending unit could be going south but most of the time they get caked up with crud from years of use and they can be cleaned with a pipe cleaner (smoking pipe type)

good luck

[Gary '79 5C]

Since I am the always the slow guy in the crowd ( WVa Native) but I need to ask is the light connected to a pressure or level sensor ??

I am thinking level, but I need to ask. I would imagine my 5C would be of the same design heritage.

Thanks

[artvonne]

Since I am the always the slow guy in the crowd ( WVa Native) but I need to ask is the light connected to a pressure or level sensor ?? Thanks

  Its a low pressure light, likely comes on around 5 psi. You can test the switch by simply grounding the wire. If the light stays lit, the circuit is fine and its the switch.

  Cleaning it with a pipe cleaner? Hmmmm.

[thomasinnv]

I do believe the mci has 2 options for low oil pressure switches. 3psi and 15 psi, with 3 psi being the most common. while grounding the sensor lead will verify the circuit to be working, it will not eliminate a possible intermittent grounding problem. could have a chaffed wire somewhere making intermittent contact to ground.

[junkman42]

Lin, My MC7 has a sensor on the side of the oil pan that indicates when the actual oil level in the pan is low>  It is possible that You have the same switch that operates along with the low oil presssure light!  My sensor is on the street side of the oil pan.  Good luck, John L.

[Lin]

No, this is the oil pressure tell tale.  I have an oil pressure sensor manifold on the driver's side of the engine.  This has the gauge sensor, which appears to be working and showing that the oil pressure is fine.  It also has a sensor switch for the tell tale light, which comes on and blinks.  It seems that that switch would only be allowing the tell tale wire to ground and activate the light.  Unfortunately, the light continues to blink even when the wire is disconnected from the sensor switch.  It seems that would that mean there is a short that is grounding my light elsewhere.  Do I understand the system correctly?

Clifford,-- I removed both sensors and cleaned the orifices.  That may have reduced the fluttering in the gauge needle.  The blinking light was unaffected.

If I decided to replace the sensor switch with a standard one from a car (that's what I think is there now), would it matter that it would be used on a 24v system?  It seems that since it is merely closing a ground circuit, the voltage would be irrelevant. 

[thomasinnv]

as long as you have the correct pressure voltage should not matter because as you said, it is only closing a ground circuit. As to your other question, yes it would appear that you have a short to ground somewhere in the circuit.

[Lin]

I tested and experimented hoping to find something ridiculously simple.  I started at the sensor manifold, then to the rear junction box, then behind the dash, and finally the front junction box.  I could not find an obvious fault.  The essential tools were a multimeter and tone generator.  The only thing to do was to use a different circuit between the front and rear junction boxes and move the sensor wire to the new stud.  It works now.  These relatively minor things can be real nuisance jobs  Fortunately there are two sensor circuits; one for an 11 psi sensor, and one for an optional 3 psi sensor, so I had one available to use.

One thing that is interesting is that the manual shows a mechanical gauge at the back end of the sensor manifold.  That port is plugged on mine.  There is however, a capped Schrader Valve in one of the ports on top of the manifold.  I assume that it is there to periodically test the accuracy of the electric dash gauge.  Could one just use a tire pressure gauge for that test even though it is oil rather than air being sampled, or is there a more specialized gauge for that?

[Len Silva]

I suggest that you disconnect the wire from the sensor and drive around for a bit.  If the light flickers even once, then you have a grounding problem and not a sensor problem.

[Lin]

Len,

I was really hoping it was a sensor problem because that is so easy to get to.  I did not want to have to start looking for the ground short.  However, no matter how hard I tried to reinterpret the facts, the bottom line kept reading as "ground".  As you know, such things can be very time consuming to find.  That is why, when it appeared that there was nothing obvious under the dash, in the two junction boxes, and at the sensor, I decided to avail myself of another circuit.  Thanks