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Old 08-13-2015, 04:23 PM
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Temp Sending Unit

TJ owner, so be gentle...

A friend has an old Willy and asked me to help diagnose a problem he is having. The Willy was down for a while and is now back up and running, but, his temp gauge is not working. Note, I don't think anything is stock on this thing. It is an aftermarket VDO gauge. When the ignition is off, it sits at mid range, as soon as he turns the ignition on it heads to zero and never moves as the temp comes up (if it does move it is miniscule change.

I was reading that to test the sending unit take an ohm reading between the 2 contacts when cold then again after a few minutes of running and I should have approximately 200 ohm swing. Going by memory here, but, I only remember one contact on the sender (or did I not look close enough? I assume with one connector I would check the resistance between the connector and group, is this correct?

Any advice on diagnosing would be great, older gentleman that I would really like to help out.

Thanks,
John

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Old 08-13-2015, 09:55 PM   #2
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I'm not familiar with that kind of gauge. Most older engines have a direct lead to the engine that is nothing more than a thermometer that the gauge reads. The only electrical components are for the light.



I was able to find a few sources that have some generic trouble shooting guides for the unit you are talking about and they all seem to read pretty much the same.

Testing Gauges
If a gauge is suspected to be faulty, the following test can be performed on VDO gauge.
1. Turn the key on:
Pressure Gauge – pointer to "0"
Fuel Gauge – pointer to amount in fuel tank
Temperature Gauge – pointer to temperature of engine water
2. With the key on, pull sender wire off the sender:
Fuel & Pressure Gauge – pointer will go to maximum right hand position
Temperature Gauge – pointer will go to maximum left hand position
3. With the key on, ground the sender wire to the engine chassis:
Fuel & Pressure Gauge – pointer will go to maximum left hand position
Temperature Gauge – pointer will go to maximum right hand position
4. All VDO electric gauge pointers peg full left hand position with the key off.


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Old 08-14-2015, 08:03 AM
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Quote:
Originally Posted by Beastmaster View Post
I'm not familiar with that kind of gauge. Most older engines have a direct lead to the engine that is nothing more than a thermometer that the gauge reads. The only electrical components are for the light.



I was able to find a few sources that have some generic trouble shooting guides for the unit you are talking about and they all seem to read pretty much the same.

Testing Gauges
If a gauge is suspected to be faulty, the following test can be performed on VDO gauge.
1. Turn the key on:
Pressure Gauge – pointer to "0"
Fuel Gauge – pointer to amount in fuel tank
Temperature Gauge – pointer to temperature of engine water
2. With the key on, pull sender wire off the sender:
Fuel & Pressure Gauge – pointer will go to maximum right hand position
Temperature Gauge – pointer will go to maximum left hand position
3. With the key on, ground the sender wire to the engine chassis:
Fuel & Pressure Gauge – pointer will go to maximum left hand position
Temperature Gauge – pointer will go to maximum right hand position
4. All VDO electric gauge pointers peg full left hand position with the key off.

Point #4 is the most telling, with the key off it is in the midrange position. This tells me that either the gauge is bad, or he has power to the gauge when the ignition is off. I will stop by with my voltmeter either tonight or over the weekend and see if we can get it straightened out.

Thanks much,
John
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2005 Wrangler X, 4.0L, 6 Speed
Zone 3" Lift - SYE Eliminator Tom Woods DS
Ford 8.8 rear, Dana 30 HP - 4.10 gears
Barricade HD Trailforce front bumper -made into a stubby
Home built rear bumper/tire carrier
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