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How to: Make Oil pressure gauge perform like "real" gauge


Elite Explorer
October 19, 1999
Reaction score
City, State
Cape Coral, FL
Year, Model & Trim Level
'91 EB
I don't know if this is a coincidence But at 1000 miles after switching to synthetic oil the oil pressure gauge reading dropped down about one letter in the normal range. Just for kicks I pulled the sending unit and cleaned out the built up crud in it and the, for lack of a better decsciption, the mounting arm or tube. Now the gauge reads exactly where it was prior.

However this is still behaving like a fake gauge. At idle or high rpm the darn thing does not fluctuate. Thus making it as useless as an idiot light.

I called Ford today to check into a new sending unit. They advise there is one for units with a gauge and one for units with just an idiot light. I also asked the guy about this fake gauge syndrome and he had never heard of it.

I have confirmed that there is good and fluctuating oil pressure with a mechanical gauge so I am not concerned about the condition of the motor. I just want a working gauge.

Does anyone know if there is a way to get a real gauge reading? Is this a function of the sending unit? Does VDO or someone have a compatible sending unit replacement?

Thanks in advance.

'91 EB, 4dr, 2wd

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Ok, sorry to bring this back up but this fake gauge has really irritated me. One way or another I am going to make this real gauge. There is no way oil pressure stays the same at idle and highway speed.

Here is what I am going to try. If anyone has additional ideas or feedback I would really appreciate it.

#1. Using a potentiometer I am going to confirm that the gauge is a real gauge. Vairing the resistance should make the needle move. I'll make recordings of high, low, lower normal and high normal resistance.

#2. Again using the potentiometer I'll take reading of the factory sending unit under various pressure loads. My guess is that this is going to be either on or off only as this would explain the needle behavior.

#3.I'll repeat this with an replacement sending unit from AutoZone.

#4. The VDO ****pit line has a gauge and electric sending unit package for about $40.00. Since the Haynes manual says that 40-60psi is normal at 2000 rpms I am going to start with the 0-80 psi kit.

#5. If I can get various readings with the VDO sending unit and gauge. I'll attach the wire from the stock gauge to the sending unit. I am sure I will have to place a resistor in line to calibrate the gauge to the new sending unit.

The VDO kit should be here next week. Will let you know how it goes.

I welcome any input.

Best regards.

'91 EB, 4dr, 2wd

Somewhere in the system is a sort of stabilizer, which allows the guage to move only slowly. Just like your fuel guage. It would be going up and down around every corner, not to mention all the splashing going on as you drive. They slow the fluctuations down so you can make a logical reading without having to manually guess at what the average fuel level is. As far as the oil guage, I am not sure how this is done, whether in the sending unit or in the dash somewhere, but it is done. I had an old mustang with a 4-banger in it whose guage started to read really low, to the point where it scared me. I tried the same as you -- put a real mechanical guage under the dash. The readings fluctuate a lot more.

But I agree with you. I hate idiot lights. I would rather see an accurate digital readout for oil pressure, voltage, amperage, coolant temperature, coolant flow, fuel pressure, air/wind speed as well as ground speed, fuel remaining, etc. Many people are satisfied with a speedo and a fuel guage. I am just too much of a "control freak" I guess, since I would like to tinker with all the engine's computer settings too.

Good luck!

Ontario Canada(!)

Hey Jambo,

I think it is even worse than a stabilizer. Mine does not move at all. Hate to admit it publicly but here is what I did. Note that there was NO MOVEMENT AT ALL on the oil pressure gauge.

Secondly note that I still have a used car warranty in effect.

#1. In neutral I brought the rpm's up to 4000 (scary)

#2. Went down the road in 1st gear at 3800-4000 rpms.

#3. Pulled a bunch of plug wires to get it to run like hell.

#4. Ran the heck out of it pulling a 2000lb trailer of dirt.

My guess is that the sending unit is just open/closed unit with a preset resistance point. This way everyone reads normal unless there is no pressure. How tacky!

I'm a control freak to. I would love to find a way to get all the computer settings to display and be controled via a laptop.

Best regards.

'91 EB, 4dr, 2wd

Sorry guys, but the gauge is an analog idiot light. The Ford Cobra forum went through this a couple of years back. I had the info to correct the problem but can't find it. I'll post more info if/when I do. I'm still looking. Can't speak to the exact presure for switch (sending unit) on the Explorer, but for the Mustang it's 5 pounds. Five pounds of pressure or more, the gauge reads right where we are used to seeing it, less than five pounds it falls all the way to the left. There is a way to fix it but it's not easy. The sending unit must be replaced with one that is specifically designed for a "real" gauge. Once that is done the instrument panel gauge will register high, off the scale. Pull the instrument cluster, cut the lead on the flex circuit that feeds the oil pressure gauge, and splice in a resistor. Here's the hard part. You'll have to experiment with different resistors until you get one that gives you a reading on the guage that will be some indication of reality. You electrical types out there should have an easier time of it and a varible resistor would make it easier too. All in all, it's probably easier to just add an additonal gauge under the dash somewhere. Not exactly what you wanted to hear, sorry. Jim

Hi Jim,

Thanks for the great news...what a pain. If you do happen to find the fix from the Cobra site I would be grateful.

Best regards.

'91 EB, 4dr, 2wd

That is pretty depressing news Jim. My Mustang has a real oil pressure gauge, and I have a spare... I wonder. If there is a way to adapt it to work in the Explorer dash I am sure that it would work. As long as the needles can be removed without damage.

Either that or put a small potentiometer in there, I think I have one of those lying around too. I may just give it a try. I'll let you know.

Paul Gagnon
Calgary, Alberta
"No Brain, No Pain"
Dead Link Removed

Technically Velveeta isn't REALLY cheese... it's a cheese food...
The stuff that other cheeses eat... I guess.

[This message has been edited by Paul Gagnon (edited 03-13-2000).]

I don't know if this is a function of the gauge itself or the sending unit. There was a discussion on this subject in usenet a few months ago, but I don't know what they determined. You may want to do a search for it and see if a solution was found.

99 Sport 4x4
Auburn Rear & Gerald's old Shackles

Good idea Tom, here is what I found.

I'm going to try the pressure sensor first. If I get the same results I'll work up the guts to rip into the instrument cluster.

In #1 below it sounds like he added a T fitting to keep the original pressure switch and add the new pressure transducer. From the original switch he hooked up a piezo which will sound should the original switch indicate low pressure. Not a bad idea..

Sorry in advance for the long post.

Best regards.

A few weeks ago there was a thread regarding the bogus oil
> gauge. It was mentioned that by adding a proper sender and
> removing a 20 ohm resistor it could be converted to a correctly
> reading gauge.

This is in the Bryan Richardson's FAQ but here's the info:

3.2. The oil gauge lie

The oil gauge on the Explorer isn't. Simply put, the indicator on the dash looks like a gauge, but it is really only a binary indication as to whether the pressure sensor believes that the engine has sufficient oil pressure or not. If it thinks there is sufficient pressure, then the gauge reads in the "Normal" zone, usually pointing to a single place (without varying based on temperature, RPMs, etc.). If there is not sufficient pressure, then the gauge reads "low." The first item below describes how to convert the "indicator" back into a gauge. Discussion on this topic follows:

Subject: Did the oil pressure modification today; it WORKS!
From: (Mike Shirley)
Organization: Muth Valley Ford Oil Pressure Check Station and Bakery

I used an "AutoTune" PT3077B transducer, $15, purchased from Kragen Auto Parts Store. It appears to be a generic application
transducer. Ford's is: Ford sender E4ZZ 9278A, $20.

I went ahead and installed the transducer today. It was a universal 1/4 pipe threaded sender with the "slip over threaded rod" style of electrical connection to the top. Plenty of room for the tee, original switch, and the new transducer. I removed the switch from the 45 degree long- shafted adapter. Used the end of the tee (not the center port) to the adapter, mounted the transducer upward and the switch outward (center port of tee). Was able to plug the original connector into the new transducer. I added a wire for the switch and ran it through the firewall and attached it to a small piezo chime via 12V+ from the switched ignition.

The gauge read just left of the N in Normal prior to disabling the 20 ohm resistor on the dash cluster. After shorting out the resistor, the gauge needle points to the A in Normal at 2000 rpm and around the O in Normal at a warm idle in gear. The needle is heavily dampened (so to react to changes) but is still a worthwhile modification.

I would say that the dash cluster removal is rather involved and not for the faint of heart. In fact, living without the resistor modification is really acceptable when you consider the gauge is dampened. If my wife would allow it, in retrospect, I'd have just done the tee and added the chime to the factory gauge but installed a real 270 degree mechanical gauge. And not touch the dash.

From: (Richard Hyde)

And now! What the manual says about the infamous OIL

"When the engine oil pressure is normal, the oil pressure switch is closed (short circuit), allowing current flow through the 20-ohm resistor on the cluster flexible circuit into the gauge which drives the pointer to a position slightly above midscale. The switch opens (open circuit) when oil pressure drops to a critically low level (4.5 - 7.5 psi) causing movement of the pointer to or below the "L" band."

"NOTE: The pointer of the magnetic gauge will remain in it's last position when the ignition is turned off. It will move to the correct (or actual) indication whenever the ignition is turned back on." Looks grim..

It looks like the cluster is trivial to remove. You have to remove the "ash receptacle" :) first. Open the "ash receptacle" and remove two screws attaching the "ash receptacle" and instrument cluster trim panel. Remove the ash receptacle assembly.

(Oops - first remove battery ground cable)

Next, unsnap the cluster trim panel by pulling rearward around the edge of the panel. Depress the hazard warning switch and remove the cluster trim panel.

Remove the four screws securing the instrument cluster to the instrument panel.

Vehicles with automatic transmissions require that the PRNDL indicator be removed.

Remove the two screws attaching the PRNDL to the cluster and slide the PRNDL down and out of the cluster. Leave PRNDL connections

Pull cluster assembly rearward to gain access to speedometer cable. If there is insufficient access to disconnect the cable at the instrument cluster, it may be necessary to disconnect at the transmission and pull the cable out far enough to disconnect at the cluster (!)

Unsnap the two wiring harness connectors and remove the cluster.


reassembly is the reverse of the above except you must:

"Apply approximately 4.8mm (APPROXIMATELY 4.8mm???) or 3/16 inch diameter ball of silicon dielectric compound (D7AZ-19A331-A (ESE-M1C171-A)) or equivalent in the drive hole of the speedometer head.

'91 EB, 4dr, 2wd

[This message has been edited by Hank (edited 03-15-2000).]

Just went thru the hassle of replacing my Oil Pressure Gauge ($72), and Ford ordered the WRONG GAUGE. it had a picture of a gas pump where my Check Engine light is supposed to be. Am waiting for the right gauge to arrive. If I had know then what I know now, I would have just put a damn light there.

I DID change out all the dashlights to RED bulbs...Looks pretty sharp at night. Will eventually get to all the other bulbs in the radio, climate control, window switches, etc

Don't Worry about things you can control...
Don't Worry about things you cannot control.

96 Eddie Bauer AWD V8

Two other cars that aren't Explorers

Ok, I just called the local Ford dealer. The part number is valid and waiting at the counter for me to pick up tonight. Will advise on how it goes.

Best regards.

'91 EB, 4dr, 2wd

I just got back from the dealer and installed the new pressure sensor. Here is what I found plus some personal observations.

#1. The new unit is much larger than the old one.

#2. It would be much easier to install on a cold engine. Anticipation got the best of me. The burns can be considered minor.

#3. As the new unit is larger it gets very close to the power steering line. I would suggest repositioning the mounting arm a bit higher. This could prevent rubbing.

#4. As the 20 ohm resistior is still installed the gauge readings are a bit low but there is noticible movement in the normal range. Idle is right on the lower normal line and cruise is about halfway between the normal line and the N. However if you turn the ignition off then on. (To simulate no oil pressure) The gauge does drop down to the red.

#4. The mounting arm for the pressure sensor hangs down from the motor. It seems like this is/would be a great place for sludge to collect. I noticed that the first bit of oil that came out when removing the old sensor was really dark and scummy. Could anyone see a problem with adjusting the arm level or upward, as room applies, to allow the oil in the arm to drain back down?

Until I am comfortable that the unit is not hitting the power steering line I am going to carry the old one, some wrenches and oil with me. I drive short distances and will check it frequently for signs of rubbing or stress. As soon as I can, I'll adjust the mounting arm to position the unit further away from the power steering line.

Next step, when I work up the guts, is to remove the resistor.

Will keep you posted.

Best regards.

'91 EB, 4dr, 2wd

[This message has been edited by Hank (edited 03-16-2000).]

This explains the oil pressure readings I was getting when my gauge showed zero and the engine started to make some (more, already had a noisy lifter) noise. My gauge showed normal on my trail ride and when I looked at it after a mud hole it showed zero. I have (finally) taken the engine apart and found the oil pick up clogged with sludge,etc.- jarred loose on the ride? or built up over a period of time? If I had a working gauge I may have known what was about to happen.
Damage to engine was actually not too bad - lifters shot, rocker arms and shafts worn but not totally destroyed. Using castrol syntec may have saved the day, but I dont know where the sludge came from. I think that my engine got some oil though the pick up- enough to keep the bottom end from locking up, but not enough to get to the top end. A real gauge may have alerted me to the pending problem- then again maybe not!
My guess is that the solid lifter history of the engine is the reason not much oil gets to the lifters and top end, ie the reason for the lifter problems in the 4.0 everyone seems to experience.

Just rambling again

Thanks for the info

Steve VB
91 Navajo
2 1/2" Rancho,
31" Goodyear AT/S

Steve, you bring up an interesting and scary point. As I said above my original pressure sensor plugged up shortly after switching to synthetics.

I've owned the explorer for two oil changes now. The dealer used regular dino oil when I bought it and again when I got them to fix the vacuum modulator. In both cases I was fairly close to 3000 miles and the oil was really clean. I just checked the condition of the synthetic oil today (1600 miles) and it is really dark. I guess there may be some truth to synthetics having a higher level detergents in them.

A while back somone mentioned that they took their Explorer to a Subaru dealer that had an oil system back flush machine. Basically they pump heated solvents and oils through the oil filter housing and then vacuum it and the sludge out from the oil drain plug. He claimed that he saw a noticible improvement. I also recall him saying something about no more lifter noise...

If these things have a sludge buildup habit I may consider trying the back flush service. The dealer wants $129.00 for it so I am going to be there and watch them do it. I used to be a GM mech. and the dealership had a bad habit of charging but not performing gravy work like this.

I'll see if I can get in there next week.

Best regards.

'91 EB, 4dr, 2wd

bringing this up for currnt ?s .

Part #'s??

I admit to getting confused about part #'s for working sending units - I got clear that Ford wants $72 for a real pressure sending unit, so what is the generic $15 or Ford $20 unit for??

VERY INTERESTING THREAD!!! Thanks VERY much for bringing this back into circulation!


PS Seems like my Ranger is due for a sensor upgrade as well!

Hello Brian,

The $72.00 he was talking about was for the gauge. You don't need that. I paid about $20 or whatever I wrote above for the Ford unit.

I've been really lazy lately and still have not pulled the 20 ohm resistor.. Someday, maybe soon.

Best regards.

Ok, finally got a real in dash guage for myself. Put the new sending unit on ($20) and tore into the instrument panel. There are 2 resistors on the back, big (physical size) too. One is on the top, one is on the bottom. If you look on the circuit sheet to the right and lower, you will see a resistance for each one, top being 20 ohm, the bottom being either 520 or 540 ohm, I can't recall which. Ayhow, you need the top one. I just took it out and soldered a new wire in it's place. The hardest part is just getting the speedo cable out, for me at least. If I had some pipe cleaner arms, it would be a lot easier.

New guage reads N at idle, R at 2000+ RPMs


Way to go Ben!

It sure is more comforting seeing that gauge move rather than always pointing at the sky....

Best regards.

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I watched it while driving today, damn thing is going to make me run off the road it's so nice to watch. It took me a while on the dash piece, but 60% or so of my trouble was trying to figure out how to get my radio back out. When I put that radio in last year, I don't think I ever anticipated taking it apart again. Sure wish I hadn't bent the tabs out on the DIN sleeve when I put it in, oh well. Hank, you were right, I had to push the power steering lines around to get the wire on the sending unit. An elbow before the sending unit will probably go on there when I get back under the car, I don't like it being up agaist everything like that.

Good luck on yours,


P.S. Did you get around to having your engine oil system flushed? I'm thinking strongly about it for the next oil change myself.