Scary Oil Pressure Discovery

[Matt400]

In doing research in one area I stumbled across an interesting find in another that bothers me...



I found that if the coolant temp sensor sees a simulated elevated temp, that data will also produce a reduced oil pressure reading regardless of the actual oil pressure.



While it is understandable that oil pressure will drop as the oil heats up I found that it will drop simply from what the coolant temp has to say.



This find makes me want to install an aftermarket oil pressure gauge that reads pressure direct.

I don't like the fact that my OE pressure gauge is being told where to read based on coolant temps, whats up with that?



I found this out working on a circuit that fools the ECM into thinking the coolant temp is elevated so I can turn on the Vistronic Fan and help cool the trans when backing a trailer.

 

[Boonieman]

I totally agree about the simulated or "virtual" oil pressure gauge on our trucks. It is one of the goofiest things I've ever heard of. Dodge isn't the only ones doing it either.

 

[rbattelle]

First gauge I purchased for this truck was oil pressure.

 

[A Johnson]

Most Cummins engines will turn on the fan when coolant temp is unplugged. Not sure if this works with the Dodge system though. Downfall is you will log a fault while it is unplugged, and engine will derate. Shouldn't matter when backing a trailer though.



Just kind of a simple way to do it if you don't mind the check engine light on. Just wire a switch to open the coolant temp circuit.



A Johnson

 

[Pawpaw]

This is a link to where I was educated about the idiot gauge light.



https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=98962

 

[y-knot]

Stupid, stupid design..... as long as the ecm is seeing at least 6 psi of oil pressure, the computer tells the oil pressure indicator to position it's needle at a point where most people would feel comfortable, somewhere in the 40-45 psi range. Does this make any sense to anyone?? That is like telling someone it's a perfect day, with perfect weather everyday of the year, regardless of what you see out side. Sounds alittle to Communist for me

 

[rbattelle]

Knot,



Obviously we as consumers don't have the intellectual capacity to determine what "good" oil pressure is. We should be thankful that giant bureaucratic companies like DaimlerChrysler are around to keep us stupid-heads from screwing something up.

 

[A Johnson]

Cummins changed to a switch some time ago. Shortly after introduction of the ISB, there were all sorts of issues with low oil pressure faults, most happening in the first 1000 miles and most under 100 miles. It was all related to the sending unit or connector, and they could not figure out how to make the sending units last. (Believe me, they tried and I'm not sure they ever understood the problem) It also happened with the ISC engine. I guess they have enough confidence in the reliability of the oil pump and engine to put a 6PSI switch in and call it good. If you look on a computer monitor screen it always shows 55. 1 PSI.



The good news is there is very, VERY rarely a problem with bearings or anything else in these engines, caused by a fault in the oil system.



Personally if I had warranty I would not worry about it, and if out of warranty would install a gauge of some type.



It is not too uncommon to see 10-12 PSI at a hot idle when RPM is <700 rpm, in my opinion.



A Johnson



P. S. I can't remember if the 03 and up engine had higher volume oil pump or not.

 

[Matt400]

Hrmm, I had no idea. The factory manual shows a variable resistor for the so called "switch".



This reminds me of the Slots in Vegas where they designed the lever you pull to "simulate" the pull/feel of the older style slots giving you the feeling you are spinning the wheels on the machine.

Actually the handle is not connected to the wheels and when you pull it far enough down a switch trips a solenoid that spins them.

The ratchet feel is all simulated with a fake ratchet.



Same machine as the push button ones but with a fake ratchet so pulling it hard or slow etc. is all in your head



Got me scratching my head now and am gonna test that switch anyway. Thanks everyone.



Edit: Actually why bother. . I just checked the manual and its true about the 6psi, from there rpms's and coolant temp command the needle for customer satisfaction