Oil pressure sending unit question (1 Viewer)

[mbplace]

Had an issue with my oil pressure sending unit — worked fine for a couple years then when I got the oil changed it would be pegged on the high side.

Took a manual reading and it was writhing the normal ranges so naturally I replaced the sending unit. Now with the new unit I get no reading at all. Does it take a while for these things register a reading when fresh or did I get a dud?

Also my wiring looks fine, new wiring harness and no issues with the other gauges

 

[charliemeyer007]

Mine never worked right even after replacing the sender. Never fooled with the meter. I made a bracket and mounted a direct read gauge on the steering wheel shaft. From the back of the gauge to the engine side of the fire wall I put the oil pressure tubing inside fuel hose - that way if the tubing failed I didn't get a face full of hot oil. Still there since about 1984 and still working fine. I did wire it so its lighted with running lights.

 

[Malleus]

Those gauges never worked. Reliably.

 

[45Dougal]

Those gauges never worked. Reliably.

The oil pressure gauge is about the only thing on mine that does work reliably haha.

Id guess that the wiring in the engine bay has been disturbed and gone open circuit somewhere.

Perform the test in the manual.

 

[Mark W]

For starters, what year is your rig and which sending unit did/do you have (with or without the spade connector on the side for grounding)?


Mark...

 

[mbplace]

For starters, what year is your rig and which sending unit did/do you have (with or without the spade connector on the side for grounding)?


Mark...

Hey there — it’s a 77. Had the one without the ground (was told that grounds to the engine block thru the threads). Replaced that with the same one and now neither work, very odd. All signs point to a bad ground but having trouble testing that

I’ve removed and replaced the old one several times to get a manual reading so not sure what the issue is now

 

[45Dougal]

What happens when you perform the test in the manual?

 

[Mark W]

Hey there — it’s a 77. Had the one without the ground (was told that grounds to the engine block thru the threads). Replaced that with the same one and now neither work, very odd. All signs point to a bad ground but having trouble testing that

I’ve removed and replaced the old one several times to get a manual reading so not sure what the issue is now

Okay, so on the old one there was chance of making the mistake of attaching the sensor wire to the ground tab. Because it was not there. And on the new one, you knew better than to do that. The sensor was never attached to the spade tab, always to the center post. yes?

Any possibility that it was accidentally grounded at some point?

If the sensor wire goes get grounded while the ignition is turned on the gauge will read full high pressure, and it will over heat, sometimes actually bending the needle. Afterwards it will read extremely low, possibly on the zero mark, no matter how much pressure it is actually sensing.

If you have a bad ground... as in lack of ground, then the gauge will also never come off the low mark. But the initial problem (pegged high) could not have been caused by lack of ground.

I have not encountered it, but *if* a failed original sending unit had resulted in a full time grounding (It works by creating a repeating temporary ground) than this could have overheated and damaged the gauge just like if the wire had been directly grounded.

When this happens to the gauge, you can often repair it by re-bending the needle. This actually is usually the failure point in the gauge.


Mark...

 

[mbplace]

What happens when you perform the test in the manual?

Grounding the sender lead to see if the gauge responds? Will try tomorrow if weather permits and report back

 

[45Dougal]

Grounding the sender lead to see if the gauge responds? Will try tomorrow if weather permits and report back

I don't have the manual in front of me but iirc it involves using a test light to test both the sender and the gauge.
You do have the original toyota chassis manual?

 

[mbplace]

Grounding the sender lead to see if the gauge responds? Will try tomorrow if weather permits and report back

gauge is maxed out when I do this so seems like it has to be an issue with the sensor itself or with it being grounded. Am I missing something with these sending units that don’t have the separate ground?? Was under the impression that they ground thru the threads. I even attached a separate wire to ground at the treads and didn’t get any movement

Also for the gauge, feel like I’d still atleast see a little bit of movement on the dial - now it just stays completely dead.

 

[mbplace]

I don't have the manual in front of me but iirc it involves using a test light to test both the sender and the gauge.
You do have the original toyota chassis manual?

I have the Haynes and it’s got the same instructions

 

[45Dougal]

The toyota manual is here somewhere to download for free - it's worth getting a copy

 

[charliemeyer007]

Land Cruiser Factory Service Manuals (FSMs)

Factory service manuals (FSMs) for your Toyota Land Cruiser ! From the 1950s to the present!

www.cruisercult.com

 

[mbplace]

Okay, so on the old one there was chance of making the mistake of attaching the sensor wire to the ground tab. Because it was not there. And on the new one, you knew better than to do that. The sensor was never attached to the spade tab, always to the center post. yes?

Any possibility that it was accidentally grounded at some point?

If the sensor wire goes get grounded while the ignition is turned on the gauge will read full high pressure, and it will over heat, sometimes actually bending the needle. Afterwards it will read extremely low, possibly on the zero mark, no matter how much pressure it is actually sensing.

If you have a bad ground... as in lack of ground, then the gauge will also never come off the low mark. But the initial problem (pegged high) could not have been caused by lack of ground.

I have not encountered it, but *if* a failed original sending unit had resulted in a full time grounding (It works by creating a repeating temporary ground) than this could have overheated and damaged the gauge just like if the wire had been directly grounded.

When this happens to the gauge, you can often repair it by re-bending the needle. This actually is usually the failure point in the gauge.


Mark...

Mey mark

Okay, so on the old one there was chance of making the mistake of attaching the sensor wire to the ground tab. Because it was not there. And on the new one, you knew better than to do that. The sensor was never attached to the spade tab, always to the center post. yes?

Any possibility that it was accidentally grounded at some point?

If the sensor wire goes get grounded while the ignition is turned on the gauge will read full high pressure, and it will over heat, sometimes actually bending the needle. Afterwards it will read extremely low, possibly on the zero mark, no matter how much pressure it is actually sensing.

If you have a bad ground... as in lack of ground, then the gauge will also never come off the low mark. But the initial problem (pegged high) could not have been caused by lack of ground.

I have not encountered it, but *if* a failed original sending unit had resulted in a full time grounding (It works by creating a repeating temporary ground) than this could have overheated and damaged the gauge just like if the wire had been directly grounded.

When this happens to the gauge, you can often repair it by re-bending the needle. This actually is usually the failure point in the gauge.


Mark...

think you might be onto something here… can’t even see the needle on the gauge when the engine is off now….

Looking thru older pictures it appears to sit just below the L…… frustrating!

 

[Mark W]

Mey mark

think you might be onto something here… can’t even see the needle on the gauge when the engine is off now….

Looking thru older pictures it appears to sit just below the L…… frustrating!

This just about confirms a bent needle. Which just about confirms that the gauge got grounded somehow and pushed the needle beyond "pegged at high. Extreme confidence.

It can *almost* always be fixed by opening it up and carefully rebending the needle.

Mark...

 

[mbplace]

This just about confirms a bent needle. Which just about confirms that the gauge got grounded somehow and pushed the needle beyond "pegged at high. Extreme confidence.

It can *almost* always be fixed by opening it up and carefully rebending the needle.

Mark...

Mark can’t thank you enough, you nailed it! Pulled off the panel, bent the starting position for the needle to read L and now idle it’s in the middle of the gauge. Such a relief

 

[ToyotaMatt]

Had an issue with my oil pressure sending unit — worked fine for a couple years then when I got the oil changed it would be pegged on the high side.

Took a manual reading and it was writhing the normal ranges so naturally I replaced the sending unit. Now with the new unit I get no reading at all. Does it take a while for these things register a reading when fresh or did I get a dud?

Also my wiring looks fine, new wiring harness and no issues with the other gauges

I wonder why the person when you got you oil changed pulled off the panel, bent the starting position for the needle like it would be pegged on the high side for you ?

that's not kool .........