Can't get my oil sender unit to work that came back from N. Hollywood Speedo. Checking the ohms
reading on my sender, resistance is over 1000 ohms. Is this standard? The one I ordered from Stoddard has
the same resistance. Using a potentiometer (dialing down to 50 ohms) the gauge works. Joe Leoni recommends
a max resistance of 200 ohms. Sent the gauge and sender back to N. Hollywood to recalibrate and they say
it's correct. Anyone with ideas? Thanks Bruce
Oil sender resistance 356C
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Greg Bryan
- 356 Fan
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Re: Oil sender resistance 356C
Bruce - Did you fix your problem? Only thing that occurs to me is the instrument ground ...
Greg Bryan
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BruceGoodrich
- 356 Fan
- Posts: 11
- Joined: Mon Jul 22, 2013 12:38 pm
Re: Oil sender resistance 356C
*****Oil Temperature Gauge (temperature and resistance)*****
--|---------|---------|----------------------|-------------|-
160°____180°___210°_____________240°_______260°
96Ω_____68Ω___43Ω______________23Ω________18Ω
Unable to get any movement from my temperature gauge after it was recalibrated by a VDO calibration shop,
I focused my attention on the sender unit which I found registered around 1040 ohms (Ω) resistance at room
temperature. I notified the shop about the high resistance and was sent another sender. This one registered
around 750 ohms resistance. However, after I hooked up the new sender the gauge still did not appear to work.
Searching for a solution, an old college roommate of mine (elec. engineer) brought over a variable resistor which
he said could be used in place of the sender to verify if the gauge was registering correctly. But we first needed
to develop a scale in order to correlate various oil temperatures with changes in amount of resistance of the sender.
Accordingly, with the sender unit immersed in cooking oil, we steadily increased the temperature of the oil, noting
both changes in temperature and changes in resistance of the sender (measured with an ohms meter). We
recorded temperatures ranging from 160° to 260° Fahrenheit with corresponding changes in resistance ranging
inversely from 96 ohms to 18 ohms (see scale above).
Next, in order to assess whether the gauge would work by changing resistance, we inserted the variable resister
and ohm meter in place of the sender and its electrical lead to the gauge. With the power on, we adjusted the
resistance (per the ohms meter) to conform to the temperatures listed in the scale above. As it turned out, the
gauge registered as it should (per the scale) which proved to us that it was actually working! I believe the reason
the gauge did not register originally was due to the fact that I never brought the car up to its normal operating
temperature which evidently takes more time than most water-cooled cars.
Bruce Goodrich
356C
--|---------|---------|----------------------|-------------|-
160°____180°___210°_____________240°_______260°
96Ω_____68Ω___43Ω______________23Ω________18Ω
Unable to get any movement from my temperature gauge after it was recalibrated by a VDO calibration shop,
I focused my attention on the sender unit which I found registered around 1040 ohms (Ω) resistance at room
temperature. I notified the shop about the high resistance and was sent another sender. This one registered
around 750 ohms resistance. However, after I hooked up the new sender the gauge still did not appear to work.
Searching for a solution, an old college roommate of mine (elec. engineer) brought over a variable resistor which
he said could be used in place of the sender to verify if the gauge was registering correctly. But we first needed
to develop a scale in order to correlate various oil temperatures with changes in amount of resistance of the sender.
Accordingly, with the sender unit immersed in cooking oil, we steadily increased the temperature of the oil, noting
both changes in temperature and changes in resistance of the sender (measured with an ohms meter). We
recorded temperatures ranging from 160° to 260° Fahrenheit with corresponding changes in resistance ranging
inversely from 96 ohms to 18 ohms (see scale above).
Next, in order to assess whether the gauge would work by changing resistance, we inserted the variable resister
and ohm meter in place of the sender and its electrical lead to the gauge. With the power on, we adjusted the
resistance (per the ohms meter) to conform to the temperatures listed in the scale above. As it turned out, the
gauge registered as it should (per the scale) which proved to us that it was actually working! I believe the reason
the gauge did not register originally was due to the fact that I never brought the car up to its normal operating
temperature which evidently takes more time than most water-cooled cars.
Bruce Goodrich
356C