Temperature gauge puzzler

[Randall Bograd]

My temperature gauge does not work.

Here's what I've tested:

The wiring is correct.
I've just replaced the sending unit.
There is juice to the negative terminal of the gauge and when I ground
the positive, the needle moves to the left.
I've checked continuity to the sending unit and that's okay.
With the car running, I've grounded the wire at the sending unit and
again, the needle moves.
I believe I let it run long enough to heat up (10 minutes), but no
movement.

Any ideas?

Randy
Blue '67

 

[WB6WSN]

----- Original Message -----
From: Randall Bograd
To: amphicar-lovers@yahoogroups.com
Sent: Wednesday, April 07, 2004 5:24 PM
Subject: [amphicar-lovers] Temperature gauge puzzler


My temperature gauge does not work.

Here's what I've tested:

The wiring is correct.
I've just replaced the sending unit.
There is juice to the negative terminal of the gauge and when I ground
the positive, the needle moves to the left.
I've checked continuity to the sending unit and that's okay.
With the car running, I've grounded the wire at the sending unit and
again, the needle moves.
I believe I let it run long enough to heat up (10 minutes), but no
movement.

Any ideas?

Randy
Blue '67



Set you multimeter to the Ohms position (to measure resistance). Connect the
meter between the temp sensor terminal (remove the wire from the gauge) and the
engine block (or any convenient ground). Measure the cold resistance of the
sensor. It should be about 100 ohms. Now run the engine until the thermostat
opens (you will feel hot air coming off the radiator). Now measure the sensor
again. This time, you should have a much lower resistance, maybe about 20 ohms.

If you are seeing no change in the reading, then the sensor is bad.

I don't know what the calibration curve is, but the sensor typically contains a
negative temperature coefficient thermistor. When the sensor is cold, the
resistance is about 100 ohms; at full hot, the sensor will be much lower, like
in the tens of ohms. If the sensor has failed open, you will see a very high
resistance at all temps (like greater than 1 Megohm).

There's no way to fix the sensor, just get a new one.

Ed
El Cajon
67 Rust Guppy


[Non-text portions of this message have been removed]

 

[Tom Maruska]

From the shop manual
"To find a defect in the temperature unit, disconnect the cable at the
temperature unit and ground it. If the gauge reacts, then the
temperature unit must be replaced."

Randall Bograd wrote:

> My temperature gauge does not work.
>
> Here's what I've tested:
>
> The wiring is correct.
> I've just replaced the sending unit.
> There is juice to the negative terminal of the gauge and when I ground
> the positive, the needle moves to the left.
> I've checked continuity to the sending unit and that's okay.
> With the car running, I've grounded the wire at the sending unit and
> again, the needle moves.
> I believe I let it run long enough to heat up (10 minutes), but no
> movement.
>
> Any ideas?
>
> Randy
> Blue '67
>
>
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[rdboggie@juno.com]

Thanks Ed.

 

[rdboggie@juno.com]

Which it does and which I did. Just put in a brand new unit. I suppose it could
be defective.

 

[WB6WSN]

----- Original Message -----
From: rdboggie@juno.com
To: amphicar-lovers@yahoogroups.com
Sent: Thursday, April 08, 2004 12:47 PM
Subject: Re: [amphicar-lovers] Temperature gauge puzzler



Which it does and which I did. Just put in a brand new unit. I suppose it
could be defective.


The proof is in how the sensor reacts to temperature.

Cold, high resistance, low current, little gauge movement.
Hot, low resistance, higher current, much gauge movement.

When you short the sensor cable to ground, this is the ultimate low resistance,
which is the equivalent of very hot, so the gauge should go to full scale.

BTW, don't put Teflon tape on the sensor threads; the threads may not make a
good ground to the block.

Ed
El Cajon
67 Rust Guppy


[Non-text portions of this message have been removed]