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Variable Oil Pressure Gauge Modifiction

DILLARD000

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Buy Cluster with DarkGray Gauge BackGround, so that 4WHi & 4WLo icons don't show;
then just don't install 4WHi & 4WLo indicator lamps for your 2WD truck.
Unsure about Cluster mods for converting OilPressureNeedle from On~Off to a true VariableGauge.
 


Stinky_Sullivan

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Welcome to TRS :)

Yes, you can use 1996-2003 cluster to replace 1999 cluster, 2WD or 4WD doesn't matter, or manual/auto
But where is the resistor that requires the bypass on this 2000 4x4 cluster? It’s not the same as the one in the How-To.
 

RonD

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I don't think it can be done on later clusters, 1996 and up
But never tried myself
 

Stinky_Sullivan

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I don't think it can be done on later clusters, 1996 and up
But never tried myself
I have no doubt the oil pressure gauge works the same on both clusters. The technology didn’t change. The only question is which resistor to jumper.

If I had a ‘95 Ranger and I were to replace the oil pressure switch with an oil sending pressure sending unit without jumpering the resistor, what would happen?

Likewise, if I were to jumper the resistor without replacing the oil switch, what would happen?

the answers to those questions will help locate the resistor in the oil pressure gauge circuit.
 

RonD

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PS60, or similar pressure sender is a variable resistor, vs a pressure switch sender which is on/off

They both use the vehicle Ground as the control, i.e. oil gauge gets 12volt with key on, if gauge is not grounded by sender then it shows 0 pressure

When there is oil pressure above 5psi, the switch sender is on/closed, grounded, so that ground passes thru the cluster's resistor and oil gauge gets a "partial" fixed ground, and gauge shows 1/3 to 1/2, depends on vehicle voltage 13.5 to 14.5volts

The PS60 is also a resistor, but resistance changes with oil pressure, low pressure is high resistance, higher pressure lower resistance, like a volume control or light dimmer
If used in line with clusters resistor the gauge needle most likely would stay on 0 since the Ground resistance would be too high to get any movement
If you REVed the engine to get higher oil pressure, so PS60's resistance value dropped, you "might" see some movement of the needle, but under normal operation it would just stay at 0

When Ford switched to the oil pressure switch in the late 1980s it was to stop the silly customer complaints of low oil pressure, and it worked

So after 6+ years they decided to stick with the switch(on/off) setup
And it was my understanding that in 1995, when the clusters were redesigned, the newer oil pressure gauges had an internal resistor, so no external resistor was used, so no way to "jumper it"
1995 was an oddball year for clusters, different than 1994 and 1996, so it may or may not have the external resistor, I don't think 1996 and up had it


Oil pressure is the oil the engine CAN NOT USE at that moment
You are seeing the pressure in the main oil passage as it builds up because the bearings and valve train can not use it, its BACK PRESSURE
Engines need a minimum of 5psi back pressure to over come gravity to keep valve train lubed, under 3psi you will usually start to hear "ticking" from valve train
Ford's pressure switch is set at 5.5psi, +/- 0.5psi
At higher RPMs more bearing cooling is needed so a higher back pressure is good, above 30psi is fine, anything more is just for "show", lol
Above 70psi and you can "wash" bearings, basically they can run dry because oil is spraying in/out too fast so is not coating and cooling the bearings, it turns into a "mist" instead of a stream, and you get spun and failed bearings
 
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Stinky_Sullivan

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There are some assumptions there which mean they’re not certainties. But let’s conclude they are.

The gauge on the ‘96-later cluster with no tach rotates in a clockwise direction while the cluster with a tach rotates in a counter clockwise direction. Likewise, the gauge on the ‘95 cluster rotates in a counter clockwise direction. Can the functional part of the ‘95 gauge be transplanted to the ‘96 cluster with the tach? That would give the ‘96 tach cluster a non resistored oil pressure gauge.
 

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You would need to pull the oil gauge and give it 12v and a ground, if needle goes to full then it uses an external resistor
If it goes to 1/3-1/2 then its an internal resistor

You could install a separate gauge on A pillar, digital oil pressure, digital temp and digital volts are very good to have
Needle gauges are OK but if you want info you can't beat actual NUMBERS, lol
 

Stinky_Sullivan

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I can definitely test my cluster for the internal resistor. I don’t mind going with the A-Pilar mounted gauges if someone makes a Ranger specific A-Pilar trim piece for those gauges. FWIW, I prefer analog over digital.
 

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I just happened to have my dash torn apart to install a Vintage Air A/C system so I'm doing the mod on my 1992 and I already had the new sender unit sitting in my spare parts (since it didn't give a trustable reading without the mod I had installed a mechanical gauge). Thanks for the write-up!
 

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Surprised to see people are still commenting on this... go figure. Swung by here to link it to a discussion on a different forum involving relocating oil pressure sensors with pipe fittings.

Still own and drive the 1995 4.0... and the oil gauge still works great. The only "issue" I've had was for some reason in a traffic jam last weekend my idle kept dropping to 500rpm or so with the A/C on and both my battery and oil gauges started dancing. Oil level was fine (the 4.0 leaks a bit, and probably burns a bit too). Once at speed there were no more issues, thankfully... and it hasn't done that since (may be related to the 130A alternator and PWM E-Fan swap I did, but that's another discussion). Edit- That's probably an IAC valve issue per another thread. Not a gauge fault per se.

One other thing I'll note: If I were to do this to my 4.0 again, I'd probably just get a replacement connector pigtail for the sending unit and splice it in rather than using ring terminals and bolts. I had to replace one of those connectors on my 1984 F150; the engine was out for a rebuild and as part of the engine removal I found the dashboard coolant sensor connector was wasted; a PO hacked up a lot of the wiring (stripped insulation to test 🤬) and that was one of many connectors too far gone to save. IIRC it wasn't expensive if one shopped around ($10 I think?) and would in hindsight result in a cleaner install. Not that I'm looking to fix what ain't broke on mine (unless/until the day comes that I find one not rotted away and start swapping things, that is).
 
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