>I have now fitted the second NOS temp. sender to my 151 A1 and the system
>still does not work.
>
Hello Gavin:
Here is some info I have compiled through my travels....
The sender is just a resistor that changes value (alot) with a change
in temperature. No moving parts like in the Oil Sending unit.
AND, they are not what you would call, a precision unit.
Via TM 9-2320-218-20 (one of the M151 manuals) page 2-78:
160 about 1200 ohms
180 917 ohms
240 450 ohms
Shorting the sender lead to ground should cause the gauge to peg to
the left, COLD side.
Leaving this lead unconnected, will cause the gauge to go to the right, HOT.
BUT....I have had a gauges on the bench while making these simple tests.
I found that with the sending lead unconnected, the gauge will do some
funny things.
I would ammend the text to read, insert a 5000 ohm resistor between the
sender end to ground: gauge should read FULL scale, HOT.
Now, what I have learned: The actual resistance values can vary as much as 20%
for the sending unit for given temperature. This applies to the old M and
new M series gauges: Metal shell connectors/ Rubber shell connectors.
Here are some tabulated values for some common M gauges:
M38/A1/M211 M715/M35As
60 2000 ohms 120 2000 ohms
200 630 140 1400
260 360 160 1200
180 1000
200 760
220 660
240 560
Using these values, at the engine end, with a resistance box,
you can determine if the gauge and its associated
circuitry are in proper order.
One other note, within the gauge, there is a mechanical ground connection
that must be functional. This means that the case must also make a good
electrical ground to the panel, which must make a good electrical ground
to the cab and , well, you know the rest.
If the internal gauge ground is questionable, you can CAREFULLY, disassemble
the unit, correct the problem, then devise someway of reassembling it
without to much moisture in it.(It is a sealed unit, and they will
otherwise frost when the case gets warm but the plastic face is still cold.)
My thoughts: I have found the M gauges to be very reliable.
I have been able to mix and match the temp gauges/sending units with good
results.
When my thermostat went bad, stuck open, the gauge read low. When
my thermostat is operating correctly, 160 or 180 degrees, my gauges showed
that to.
(Much more so then my wife's car, 93 Chrysler, gauges. They have no gauge
values, just needle movement.) OK if you take note and drive it everyday.
Hope this helps you.
Ted H. MVPA 1705
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