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Posted: Thu Nov 30, 2017 10:06 am
by wesk
My test method above is the most reliable available. Even the TB 9-2300-228-20 Troubleshooting guide does not offer hard resistance readings for hard parameters. I have found no official listings for OHM values for any of the senders. The values listed after the end of the Trouble Shooting guide were Bob's values for his senders.
Chart of resistance checks done on operational components. All resistance checks are done with the component out of the circuit.
Temperature Sending Unit - resistance to yield corresponding gauge readings
2000 ohms = 120F
900 ohms = 180F
450 ohms = 220F
300 ohms = 260F
Fuel Level Sending Unit - resistance to yield corresponding gauge readings
30 ohms = Full
15 ohms = Half
0 ohms = Empty
Oil Pressure Sending Unit (120 psi gauge) - resistance to yield corresponding gauge readings
0 ohms = 0psi
12 ohms = 30psi
30 ohms = 60psi
50 ohms = 90psi
90 ohms = 120psi
Divide psi readings by 2 for 60 psi gauges
Even using Bob's numbers a 60 degree reading would be about 3,000 to 4000 Ohms.
Resistance at both early & late gauges also varies with ambient temperature.
Posted: Thu Nov 30, 2017 12:20 pm
by 4x4M38
The temp sender readings above correspond with Radtech's
later sender reading at ambient.
The early sender we have in hand reads considerably lower in resistance
at ambient.
Posted: Thu Nov 30, 2017 12:43 pm
by wesk
And the exact ambient temp that those recordings were made at is???????????
Posted: Thu Nov 30, 2017 1:45 pm
by 4x4M38
Posted: Thu Nov 30, 2017 11:18 pm
by wesk
My point was offering up all the above listed ohm readings you guys are quoting without any reference to actual ambient air temp makes them entirely useless.
Also the internal assembly of these senders often insulates the center material from the shell. It would be wise to connect your meter's ground clip to the shell. Easiest place is the sleeve the Douglas shell connects to.
Posted: Fri Dec 01, 2017 8:20 am
by 4x4M38
Hi Wes,
Are you saying jumper from the temperature probe of the sender to the Douglas connector?
I always though the Douglas connector shells were isolated from the wire leads.
I had one side of the ohmeter clipped to the probe and one side to the Douglas pin.
Thanks,
Posted: Fri Dec 01, 2017 9:41 am
by wesk
The Douglas connector shell on the sender is isolated from the wire. Again, my point is the Douglas shell is part of the sender's shell and a better choice for a Ohm meter ground then the tip of the probe which may be isolated from the shell of the sender. It's a good electrical testing practice not an indication that the tip does not always work.
