Engine/Transmission (1998.5 - 2002) Secondary (Not instrument panel OEM) oil pressure gauge reads significantly different

[rweis]

I installed a second oil pressure gauge to cross check the instrument panel OEM indicator. There are some significant differences in the pressures, especially when the engine gets warm (water tamperature stabilizes).



Anyone else with a secondary oil pressure gauge see this?



OEM / Secondary



Idle warm 35 / 25

50 mph 45 / 60

70 mph 45 / 70



cold idle 60? / 90



The secondary gauge follows the engine rpm really well. I have even tried to set a speed (after the transmission gets shifted into O/D) watching the secondary oil pressure psi and it is fairly accurate repetatively (ie 60 psi = 50 mph in O/D).



I am taking the sensor off the line to the bypass filter which is actually somewhat open as it returns to the oil fill cap. The pressures would be even higher in a closed system I would think.



Why do you think the OEM indications are so much lower, except for warm idle?



Bob Weis

 

[n7gxz]

There was a problem a couple of years ago with the OEM sender unit and the factory fix was to program the PCM to show a mid range reading unless there was no pressure signal from the sender. They may have gotten a little more fancy with the programming to move the needle around.



Kevin

 

[AggieJustin]

Check your oil pressure sending unit and see whether it has 2 wires or 3 wires. They made a change at one point to use a 2 wire sending unit which was just a oil pressure switch that would detect when pressure dropped below a set limit. And the computer was re-flashed to work like Kevin said. If the oil pressure switch tripped, then the computer would cause the gauge to fall to 0 and light up the Check Gages light.

 

[Scrappy]

so that means we got idiot gauges?

 

[rweis]

First I have heard of that one, but with DC you never really know.



I wanted it as a backup as I am towing our 5er 2500 miles during July and did not want the situation of oil pressure going to zero and having to make a decision to do something (believe the OEM gauge and there is no oil pressure and have to shut it down NOW, or take a chance on the possibility that it is a OEM sensor failure and it is "OK") within a few seconds and 13k strapped to my butt.



Westach I can reasonably trust.



Now about the reprogramming the OEM "sensor", that would explain why the readings are so very different. The OEM oil pressure does "hang out around the middle" once the engine temp gets warmed up and stable seems to be true on my 2002 ETC.



I will have to check the 2 wire or 3 wire on the "sensor" to see if it is an 2 wire idiot light. I tend to think I do not have just an idiot light as the "oil pressure readings" do move around some about the middle.



Interesting.



Bob Weis