Low oil pressure?

[Oliver88]

My neighbor has a 2003 Ram. He has recently started noticing oil pressure well below 40 pounds at an idle. It is up over 40 while running at road speed. It is full of clean oil. Is this normal?

Thanks in advance,

Greg Davis

 

[bmoeller]

Before doing anything else, put a mechanical gauge on it, to verify. Could be a simple gauge/sender issue.

 

[Pawpaw]

The "reading" on the oil pressure gauge means exactly nothing.

You see, it's not a true oil pressure gauge. There is only an oil pressure switch on the engine. When oil pressure is above a certain level (6 psi?), it sends a signal to the computer.

The computer then manipulates the dash gauge to read "in accordance with customer expectations. "

In other words, it's a glorified idiot light. Like the man said, put a real gauge on it.

Bob

 

[Bertram65]

The "reading" on the oil pressure gauge means exactly nothing.



You see, it's not a true oil pressure gauge. There is only an oil pressure switch on the engine. When oil pressure is above a certain level (6 psi?), it sends a signal to the computer.



The computer then manipulates the dash gauge to read "in accordance with customer expectations. "



In other words, it's a glorified idiot light. Like the man said, put a real gauge on it.



Bob

This frequently gets quoted about the "customer expectations", there must be some accuracy to the gauge as mine reads higher right after I change the oil, it is also effected by ambient tempature and engine tempature, I have a hard time believing it is just a switch that is either open or closed.

 

[Matt400]

The computer then manipulates the dash gauge to read "in accordance with customer expectations. "

Based on RPM and coolant temperatures.

 

[Matt400]

I have a hard time believing it is just a switch that is either open or closed.

It is, straight from the factory manual.

 

[Pawpaw]

This frequently gets quoted about the "customer expectations", there must be some accuracy to the gauge as mine reads higher right after I change the oil, it is also effected by ambient tempature and engine tempature, I have a hard time believing it is just a switch that is either open or closed.

I had a hard time believing it too. Then I looked at the schematics. Sure enough, it's a pressure switch.

Remember, the computer has sensors to tell it what the ambient and engine coolant temps are, as well as engine RPM.

It would be pretty easy to write a routine to make the gauge work the way they want it to. It seems to me it would be even simpler to just put in a real gauge.

Bob

 

[rbattelle]

This frequently gets quoted about the "customer expectations", there must be some accuracy to the gauge as mine reads higher right after I change the oil, it is also effected by ambient tempature and engine tempature, I have a hard time believing it is just a switch that is either open or closed.

2003 Service manual volume 1 page 8J-32:



"Engine Oil Pressure Message - The instrument cluster circuitry restricts the oil pressure gauge needle operation in order to provide readings that are consistent with customer expectations. Each time the cluster receives a message from the PCM or ECM indicating the engine oil pressure is above about 41 kPa (6 psi) the cluster holds the gauge needle at a point near the middle increment within the normal range on the gauge scale"



Then on page 8J-33:

"On vehicles with a diesel engine, the ECM continually monitors the engine oil pressure sensor to determine the engine oil pressure. "



Earlier on page 8J-32:

"The oil pressure gauge is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board... The instrument cluster circuitry controls the gauge needle position... "



I can't find anything that says exactly what the pressure sender reads. I swear I've read somewhere in these manuals that the sender is just a switch.



-Ryan

 

[rbattelle]

More info

Page 8E-4, the pressure sending unit is labeled "Oil Pressure SWITCH"... I didn't add the capital letters. . it's written that way in the manual.



Same page (8E-4) under outputs from the ECM: "Oil pressure switch/warning lamp".



It's very very clear from the manual that the gasser trucks do have a real oil pressure sensor. It's totally unclear whether the diesel's do.



I find it very interesting that the cluster is programmed to trip a "check gauges" light and peg the oil pressure needle at minimum if the pressure is below 6 psi, but the manual clearly specifies minimum oil pressure on the Cummins at idle is 10 psi.







-Ryan

 

[Buzzer]

It probably is just a switch. The switch reads oil pressure at or above 5 to 6 lbs and sends a message to the ECM. The ECM then reads RPM coolent temp etc. and adjusts the guage to meet the drivers "expectations". What a bunch of crap. Just put in a real guage and be done with it. I believe a real guage would "meet our expectations". :-{}