Another oil pressure gauge thread

[Scary Fast atx]

Been reading a lot of other threads about these factory oil gauges and had some questions for you electrical gurus

My original sender was leaking, so I replaced it with a 60psi unit from Rock Auto

I replaced it, but gauge does not respond to the engine rev'ing, stays low at like 10-15psi

Tested the new sender with my radiator pressure tester to 15-30 psi and it was reading much higher than I was expecting, like 40-60ohms

I also pulled out the gauge and tested the ceramic resistor and it is open (its a pink resistor, but dont know what resistance that equates to, my googlefu couldnt pull up anything)

I ordered a 90ohm resistor and put it on the back and am trying to test it on the bench but its staying over 60psi, I was testing with an old fuel level sender that had some dead spots, so not exactly "precision instruments"

Can anybody help me out with the resistance on the oil pressure gauge (pink color)?

also has anyone seen a higher than expected oil pressure sender resistance?
(its this one https://www.rockauto.com/en/moreinfo.php?pk=939037&cc=1030723&pt=4588&jsn=18)

Thanks!

 

[SirRobyn0]

@Scary Fast atx
I'm going to try to answer your questions as best I can, then comment a little. I'll quote you then answer in italics.
"also has anyone seen a higher than expected oil pressure sender resistance?" I've seen oil pressure sending units do all kinds of strange things. I once had a 70's Dodge van into the shop, another shop had replaced the oil pump in his engine twice. Still he had the same symptoms, he'd run down the road with good oil pressure, come to a stop and the oil pressure would start to climb! All the way to the top of the scale 80psi. Other shop told him the block must be clogged and not to drive it because the oil filter might blow off. Well I already suspected his engine was fine and about 30 seconds with a test gauge set up and I knew the pressure sending unit was the culprit.

"Can anybody help me out with the resistance on the oil pressure gauge (pink color)?" No idea, and as far as I can tell it's not published anywhere, at least not anywhere I have access to. However generally speaking a failed resister would cause the gauge not to be able to reach one end of the scale or the other.

This would be what I would do for testing. I would take the wire off the oil pressure sending unit and turn the key on. With the wire disconnected the gauge should be at one extreme end of the scale or the other. Ground it out and it should peg in the opposite direction. If it fails to peg, for example won't go past that 10-15 mark, then I'd replace the resistor and the gauge. If the gauge passes testing then it's the sending unit. Also the sending unit works by completing the ground, I've seen guys put so much thread tape on them that they isolate the sending unit. If I had to take a stab in the dark based on what you have said, my bet would be the new sending unit is DOA, I also would not be surprised if you find that the gauge won't go any lower than 10-15psi area during testing.

 

[Snoots]

@SirRobyn0 is correct! NEVER use thread tape on sensors!

 

[Rickf]

You might consider "T-ing" in for a mechanical gauge for testing.

 

[AuroraGirl]

is the gauge a 60 psi gauge? or does it lack numbers?

 

[Scary Fast atx]

@Scary Fast atx
I'm going to try to answer your questions as best I can, then comment a little. I'll quote you then answer in italics.
"also has anyone seen a higher than expected oil pressure sender resistance?" I've seen oil pressure sending units do all kinds of strange things. I once had a 70's Dodge van into the shop, another shop had replaced the oil pump in his engine twice. Still he had the same symptoms, he'd run down the road with good oil pressure, come to a stop and the oil pressure would start to climb! All the way to the top of the scale 80psi. Other shop told him the block must be clogged and not to drive it because the oil filter might blow off. Well I already suspected his engine was fine and about 30 seconds with a test gauge set up and I knew the pressure sending unit was the culprit.

"Can anybody help me out with the resistance on the oil pressure gauge (pink color)?" No idea, and as far as I can tell it's not published anywhere, at least not anywhere I have access to. However generally speaking a failed resister would cause the gauge not to be able to reach one end of the scale or the other.

This would be what I would do for testing. I would take the wire off the oil pressure sending unit and turn the key on. With the wire disconnected the gauge should be at one extreme end of the scale or the other. Ground it out and it should peg in the opposite direction. If it fails to peg, for example won't go past that 10-15 mark, then I'd replace the resistor and the gauge. If the gauge passes testing then it's the sending unit. Also the sending unit works by completing the ground, I've seen guys put so much thread tape on them that they isolate the sending unit. If I had to take a stab in the dark based on what you have said, my bet would be the new sending unit is DOA, I also would not be surprised if you find that the gauge won't go any lower than 10-15psi area during testing.

thanks for the feedback

I had tested the sending unit as you had described, which is why I started digging into the cluster, thats when I found that the resistor on the back was dead.

When I run the engine and rev it, the resistance does move the way I think. I put on 1 twist of teflon tape, but Im gonna take it off and just wipe some oil on it to help it seal (yeah I have seen some people do some REALLLY silly stuff with thread tape, I had a fellow engineer argue with me that the teflon tape was the seal so it needed 3 passes, LOL)

I ended up getting a 3 gauge pod from Harbor Fright on clearance, gonna put it in and see how it corresponds to the factory gauges

You might consider "T-ing" in for a mechanical gauge for testing.

my sender is on the back of the manifold pad, Im gonna stick the other gauge on the port by the filter since its easier to get to

is the gauge a 60 psi gauge? or does it lack numbers?

yeah its a 60psi gauge

 

[SirRobyn0]

thanks for the feedback

I had tested the sending unit as you had described, which is why I started digging into the cluster, thats when I found that the resistor on the back was dead.

When I run the engine and rev it, the resistance does move the way I think. I put on 1 twist of teflon tape, but Im gonna take it off and just wipe some oil on it to help it seal (yeah I have seen some people do some REALLLY silly stuff with thread tape, I had a fellow engineer argue with me that the teflon tape was the seal so it needed 3 passes, LOL)

Your welcome, hopefully some it was helpful. This likely will not be, but is related info. In the mid-2000's certain Chrysler engines had a issue with there oil gauges dropping to zero and staying there. The problem was the red thread sealer that was put on the sending units, was enough to isolate the sending unit. Even the dealer replacements were like that, so we just got in the habit of pulling the sensors cleaning some of that crap off with brake cleaner and wire brush and reassembling.

 

[newguy11]

This seems like a relevant thread to jump onto.

I’m having a similar issue and want to test a used gauge before I open up the dashboard I can see by looking at the back of the gauge that the bottom is ground but which terminal is keyed power and which connects to the sensor?

 

[SirRobyn0]

This seems like a relevant thread to jump onto.

I’m having a similar issue and want to test a used gauge before I open up the dashboard I can see by looking at the back of the gauge that the bottom is ground but which terminal is keyed power and which connects to the sensor?

I can't answer your question but why don't you key it on and hit the terminals with a multi-meter. Your should be able to tell right quick which is which.

 

[newguy11]

I think I found my answer in the attached pic and the thread linked below.

At this point I think the culprit is a bad wire.

Oil Pressure Gauge Troubleshooting

I have a 1979 K10 with a sbc 350 and looking for some help troubleshooting the Oil Pressure Gauge. With the key off the oil pressure gauge reads 0, when in run position with engine off its at 0, when the engine is started it goes to 60 and when the engine is shut down it goes back to 0. I...

www.gmsquarebody.com

 

[SirRobyn0]

I think I found my answer in the attached pic and the thread linked below.

At this point I think the culprit is a bad wire.

Oil Pressure Gauge Troubleshooting

I have a 1979 K10 with a sbc 350 and looking for some help troubleshooting the Oil Pressure Gauge. With the key off the oil pressure gauge reads 0, when in run position with engine off its at 0, when the engine is started it goes to 60 and when the engine is shut down it goes back to 0. I...

www.gmsquarebody.com

If the "bad wire" if you think it's the one leading to the oil pressure sending unit you can try turning the key on with the wire disconnected and the sending unit and then ground it out. The gauge should move. These trucks are kind of know for gauging issues so don't over look the gauge itself or the printed circuit board on the dash, or the connector to the circuit board.

 

[newguy11]

Here is where I am at now

Manual gauge pressure : 45 lbs

GM gauge:
Key on : 0 psi
Engine running: 60 + psi
Wire grounded 0 psi
Wire open 60+ psi

Resistance across Gauge:
Without resister: 85.5 ohms
W/ ceramic resister: 45 ohms
W/ only new 91 ohm resister: 45 ohms
W/ both ceramic and new resister:
31 ohms.

I guess at this point I need to remove the sender and bench test…

 

[mibars]

Bumpong an old thread, but I just now happen to have the gauge cluster to change bulbs and inspect gauges.

My oil gauge is showing something, shows pressure with engine off, shows some different pressure with engine on, does not react to throttle. I want to bench test it while I have it out.

Which pin is doing what? I'm not sure if the diagram above is correct, with + on left post ground on bottom post it went off the scale to "80". Before I break something can somebody confirm the correct pinout?

 

[Snoots]

You must be registered for see images attach

You see that 89 ohm resistor? That should be on the back of the gauge. I have no idea what kind of kluge you have on yours.

 

[mibars]

Thank you, I have something that looks like a thick film ceramic resistor screwed to the back of the gauge, so I'll check it. My gauge reads 0 - 30 - 60, however with voltage between two posts it went way past the 60. Based on your diagram I've applied the voltage on just one of the coils which may explain why did it go all the way to the max.

EDIT: The difference I see is that the ceramic resistor is between left and right post and not between left (or right?) and a bottom one. I found the picture on a different forum and mine loos similar: