XJS oil pressure gauge
#1
03-22-2021, 03:58 PM
XJS oil pressure gauge
Hello all, looking for some help with my 1976 XJS!
The oil pressure gauge goes straight up when I turn on the ignition.
I have taken the wire off the pressure gauge and grounded it which sends the gauge to zero.
I have also taken the dash out to change all the bulbs and clean up the contacts.
I have fitted a new pressure sender and when I turn on the ignition.....the gauge goes straight to the top again. Hmmm.
Any ideas on how I can test the pressure sender or is there anything else you can suggest I need to look at?
The oil pressure gauge goes straight up when I turn on the ignition.
I have taken the wire off the pressure gauge and grounded it which sends the gauge to zero.
I have also taken the dash out to change all the bulbs and clean up the contacts.
I have fitted a new pressure sender and when I turn on the ignition.....the gauge goes straight to the top again. Hmmm.
Any ideas on how I can test the pressure sender or is there anything else you can suggest I need to look at?
#2
03-23-2021, 03:15 AM
OK,
Beer time for sure.
The Sender for the Dash Gauge is a Smiths unit, and has REVERSE polarity to a NORMAL gauge sender.
By this I mean:
Standard gauge sender = NO oil pressure, = zero ohms to earth. As oil pressure rises the Ohms reading rises as does the Dash Gauge in a normal car.
Jaguar/Smiths sender = No oil pressure = 640ish Ohms to earth. As oil pressure rises, the Ohms reading traverses to zero, and the Dash Gauge rises.
SIMPLE.
The other issue is the crossed wires with the idiot light sender, but I dont think you have that.
Take that sender, Ohms test the terminal to body, you should have around 640ish Ohms, and that is from memory, apply pressure to the small hole, air will do, NOT your mouth, your lungs are not that good, nice try but, and note the Ohms dropping as the pressure is applied. This indicates the sender is to Jag spec.
IF
The Ohms test as above reads zero, or very, very close, and the Ohms rise as the pressure is applied, the sender is NOT to Jag spec, and is a common issue with aftermarket in my 50+ years with Jaguar.
VDO Aust did make one, for an very early Nissan Skyline, that was the same reverse polarity, but I am told this is NLA. I used one on mine back in 1995, and its still working and dry.
I await the results.
Beer time for sure.
The Sender for the Dash Gauge is a Smiths unit, and has REVERSE polarity to a NORMAL gauge sender.
By this I mean:
Standard gauge sender = NO oil pressure, = zero ohms to earth. As oil pressure rises the Ohms reading rises as does the Dash Gauge in a normal car.
Jaguar/Smiths sender = No oil pressure = 640ish Ohms to earth. As oil pressure rises, the Ohms reading traverses to zero, and the Dash Gauge rises.
SIMPLE.
The other issue is the crossed wires with the idiot light sender, but I dont think you have that.
Take that sender, Ohms test the terminal to body, you should have around 640ish Ohms, and that is from memory, apply pressure to the small hole, air will do, NOT your mouth, your lungs are not that good, nice try but, and note the Ohms dropping as the pressure is applied. This indicates the sender is to Jag spec.
IF
The Ohms test as above reads zero, or very, very close, and the Ohms rise as the pressure is applied, the sender is NOT to Jag spec, and is a common issue with aftermarket in my 50+ years with Jaguar.
VDO Aust did make one, for an very early Nissan Skyline, that was the same reverse polarity, but I am told this is NLA. I used one on mine back in 1995, and its still working and dry.
I await the results.
Last edited by Grant Francis; 03-23-2021 at 04:53 AM.
The following 2 users liked this post by Grant Francis:
Doug (03-23-2021),
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#3
03-23-2021, 12:20 PM
Grant, thanks for the reply. I will try that when I get a chance.
Ohms testing is new to me (even though the art itself is ancient) - am I testing the ohms reading between the terminal of the pressure sender and the body of the pressure sender?
I had all the beers on Saturday changing the old one - what a mission that turned into!
Ohms testing is new to me (even though the art itself is ancient) - am I testing the ohms reading between the terminal of the pressure sender and the body of the pressure sender?
I had all the beers on Saturday changing the old one - what a mission that turned into!
#4
03-23-2021, 01:03 PM
The following 3 users liked this post by mghirsch:
#5
03-23-2021, 07:56 PM
Grant, thanks for the reply. I will try that when I get a chance.
Ohms testing is new to me (even though the art itself is ancient) - am I testing the ohms reading between the terminal of the pressure sender and the body of the pressure sender?
I had all the beers on Saturday changing the old one - what a mission that turned into!
Ohms testing is new to me (even though the art itself is ancient) - am I testing the ohms reading between the terminal of the pressure sender and the body of the pressure sender?
I had all the beers on Saturday changing the old one - what a mission that turned into!
Its Wednesday here, so hump day and beer day, HA.
#6
07-19-2022, 02:37 PM
Veteran Member
OK,
Beer time for sure.
The Sender for the Dash Gauge is a Smiths unit, and has REVERSE polarity to a NORMAL gauge sender.
By this I mean:
Standard gauge sender = NO oil pressure, = zero ohms to earth. As oil pressure rises the Ohms reading rises as does the Dash Gauge in a normal car.
Jaguar/Smiths sender = No oil pressure = 640ish Ohms to earth. As oil pressure rises, the Ohms reading traverses to zero, and the Dash Gauge rises.
SIMPLE.
The other issue is the crossed wires with the idiot light sender, but I dont think you have that.
Take that sender, Ohms test the terminal to body, you should have around 640ish Ohms, and that is from memory, apply pressure to the small hole, air will do, NOT your mouth, your lungs are not that good, nice try but, and note the Ohms dropping as the pressure is applied. This indicates the sender is to Jag spec.
IF
The Ohms test as above reads zero, or very, very close, and the Ohms rise as the pressure is applied, the sender is NOT to Jag spec, and is a common issue with aftermarket in my 50+ years with Jaguar.
VDO Aust did make one, for an very early Nissan Skyline, that was the same reverse polarity, but I am told this is NLA. I used one on mine back in 1995, and its still working and dry.
I await the results.
Beer time for sure.
The Sender for the Dash Gauge is a Smiths unit, and has REVERSE polarity to a NORMAL gauge sender.
By this I mean:
Standard gauge sender = NO oil pressure, = zero ohms to earth. As oil pressure rises the Ohms reading rises as does the Dash Gauge in a normal car.
Jaguar/Smiths sender = No oil pressure = 640ish Ohms to earth. As oil pressure rises, the Ohms reading traverses to zero, and the Dash Gauge rises.
SIMPLE.
The other issue is the crossed wires with the idiot light sender, but I dont think you have that.
Take that sender, Ohms test the terminal to body, you should have around 640ish Ohms, and that is from memory, apply pressure to the small hole, air will do, NOT your mouth, your lungs are not that good, nice try but, and note the Ohms dropping as the pressure is applied. This indicates the sender is to Jag spec.
IF
The Ohms test as above reads zero, or very, very close, and the Ohms rise as the pressure is applied, the sender is NOT to Jag spec, and is a common issue with aftermarket in my 50+ years with Jaguar.
VDO Aust did make one, for an very early Nissan Skyline, that was the same reverse polarity, but I am told this is NLA. I used one on mine back in 1995, and its still working and dry.
I await the results.
I tested mine and i got 250.5 ohms in either scenario. Cold engine.
This is the one I put in
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