# 1965 oil pressure sending unit resistance ?



## cij911 (Oct 25, 2017)

I needed to replace my factory pressure sending unit (0-60 psi) - the post was damaged and giving intermittent readings.

I purchased the new sending unit from Ames and was told they are 0-90 ohms ("like all other sending units" - which of course is incorrect). Unfortunately after I installed the sending unit and tested the resistance, I am not getting anything close to 90 ohms (rather more like 1000 - 1200 ohms). My dash is not installed currently as the car is being restored.

I tested the resistance by placing one lead of the ohmmeter on the output of the sending unit and the other on the battery ground.

Does anyone know what the correct resistance reading range should be for a 65'?


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## the65gto (Oct 9, 2008)

90 seems correct. I would measure from lead to the outside cover/shell of the sending unit???


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## cij911 (Oct 25, 2017)

the65gto said:


> 90 seems correct. I would measure from lead to the outside cover/shell of the sending unit???


Would you please test yours and tell me what you are getting ? Thanks

Chris


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## the65gto (Oct 9, 2008)

cij911 said:


> Would you please test yours and tell me what you are getting ? Thanks
> 
> Chris


I was half way across nebraska traveling to east coast when I noticed my oil pressure was ZERO on my rally pack . Lucky I was near a chevy dealer and had them put a mechanical gauge on it and it was normal. At a nearby "Kmart" purchased a mechanical gauge with plastic line, connected it up in the parking lot and drove it the remainder of the trip without any issues. Bottom line (shouldn't done it) but replaced the in dash gauge/sender with the mechanical and has been there for the last~ 40 yrs! Still have the intention to replace the gauge someday...so don't have one to check :-(. What was the ohms reading from terminal to outside cover on the sender. Looked in my manuals and they did not include the rally gauge troubleshooting. :frown3: Will go to my attic and look in my parts box and see if one is still there. The ohms reading you got is way off from what it should be, is it possible they gave you a sender for the idiot light configuration??


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## cij911 (Oct 25, 2017)

the65gto said:


> I was half way across nebraska traveling to east coast when I noticed my oil pressure was ZERO on my rally pack . Lucky I was near a chevy dealer and had them put a mechanical gauge on it and it was normal. At a nearby "Kmart" purchased a mechanical gauge with plastic line, connected it up in the parking lot and drove it the remainder of the trip without any issues. Bottom line (shouldn't done it) but replaced the in dash gauge/sender with the mechanical and has been there for the last~ 40 yrs! Still have the intention to replace the gauge someday...so don't have one to check :-(. What was the ohms reading from terminal to outside cover on the sender. Looked in my manuals and they did not include the rally gauge troubleshooting. :frown3: Will go to my attic and look in my parts box and see if one is still there. The ohms reading you got is way off from what it should be, is it possible they gave you a sender for the idiot light configuration??


Definitely the "correct" part. I am wondering if the unit is not properly grounding to the block and that is causing the high readings (the only thing I can think of). I have one lead of the ohm meter on the terminal and the other lead on the battery post.

Thanks

chris


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## the65gto (Oct 9, 2008)

cij911 said:


> Definitely the "correct" part. I am wondering if the unit is not properly grounding to the block and that is causing the high readings (the only thing I can think of). I have one lead of the ohm meter on the terminal and the other lead on the battery post.
> 
> Thanks
> 
> chris












Excuse my " illustration " you would eliminate any possible resistance if you did the measurement like this?? If it measures correctly like this, then I would troubleshoot from the female section of the filter to the neg terminal of the battery.?? p.s. nutin in my parts box :-(


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## cij911 (Oct 25, 2017)

the65gto said:


> Excuse my " illustration " you would eliminate any possible resistance if you did the measurement like this?? If it measures correctly like this, then I would troubleshoot from the female section of the filter to the neg terminal of the battery.?? p.s. nutin in my parts box :-(


Sorry I am confused:nerd:.....


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## the65gto (Oct 9, 2008)

cij911 said:


> Sorry I am confused:nerd:.....


For some reason the illustration disappeared, trying again. See attachment 114067 above??


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## cij911 (Oct 25, 2017)

the65gto said:


> For some reason the illustration disappeared, trying again. See attachment 114067 above??


Thanks for the picture. When the sending unit is installed, the threaded nipple is in the block and thus grounded, so the readings should be the same as connecting one lead of the ohm meter to the male output terminal (of sending unit) and the other lead to the ground of the battery.

That said, you now have me wondering if the problem is the sending unit is not properly grounding to the block!!

I have to keep digging.....


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## PontiacJim (Dec 29, 2012)

You didn't use any teflon tape, pipe dope, sealer on the threads? These can act as insulators and the sending unit will not ground.


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## cij911 (Oct 25, 2017)

PontiacJim said:


> You didn't use any teflon tape, pipe dope, sealer on the threads? These can act as insulators and the sending unit will not ground.



I did on the first one, realized it may have been an issue and removed it with no consequence. The new sending unit actually came with a sealing compound on it.


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## cij911 (Oct 25, 2017)

OK, I have done a ton of research on this and the early Pontiacs (our cars) used a non-standard oil pressure seeing unit. The factory calibration was set using a 30 ohm sending unit (vs. the standard GM 90 ohm). I have bout several units from Ames Performance and they are junk - one was DOA and the other is calibrated closer to 90 ohms. I am looking into taking one apart and rebuilding the windings to provide the OEM specification.

More to follow....


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