test / calibrate water gauge
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geoff
- Posts: 123
- Joined: Tue Jan 31, 2012 1:19 pm
- Your car is a: 1982 Spider
test / calibrate water gauge
can anyone please suggest how to test the water temperature gauge for accuracy using a DVM?
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TX82FIAT
- Posts: 1814
- Joined: Mon May 03, 2010 11:04 am
- Your car is a: 82 Fiat Spider 2000 CSO
- Location: San Antonio
Re: test / calibrate water gauge
Connect volt ohm meter’s black lead to a solid grounding point. Remove the wire from the sensor terminal and connect the red lead to the coolant temperature sensor’s terminal end. Not sure what to set the digital reading for the meter to but would suggest 20K. Turn your engine on and as the car gets up to heat the meter should read more than 200 ohms or so. For the record, I'd have top look up the ohm values for the sensor.
Buon giro a tutti! - enjoy the ride!
82 Fiat Spider 2000
03 BMW M3
07 Chevy Suburban
82 Fiat Spider 2000
03 BMW M3
07 Chevy Suburban
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Nut124
- Posts: 748
- Joined: Wed Oct 25, 2017 6:39 pm
- Your car is a: 1978 124 Spider 1800
Re: test / calibrate water gauge
With a DVM you would need the Temp vs R curves for the sender. You would have to check the gauge separately with a resistor dial box.
Temp senders are usually pretty reliable compared to say oil pressure senders. Thats because the temp sensor can be totally potted and is not exposed to the media they measure.
If you remove the sender from the head you could test the sender/gauge combo by placing the sender in a cup of hot water with a BBQ TM. Need to apply engine ground to the sender body.
Do you suspect your gauge reads off?
Temp senders are usually pretty reliable compared to say oil pressure senders. Thats because the temp sensor can be totally potted and is not exposed to the media they measure.
If you remove the sender from the head you could test the sender/gauge combo by placing the sender in a cup of hot water with a BBQ TM. Need to apply engine ground to the sender body.
Do you suspect your gauge reads off?
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18Fiatsandcounting
- Posts: 3799
- Joined: Fri Mar 15, 2019 11:23 pm
- Your car is a: 1969 and 1971 124 spiders
- Location: San Francisco Bay Area
Re: test / calibrate water gauge
Good advice in the above, and today is your lucky day since I have plotted out the resistance of the sensor versus the gauge reading. This is for earlier spiders, but I'm guessing it's the same for an '82 since replacement sensors are the same from 1966 through 1985.
A sensor reading of 40 ohms or less will result in a full scale reading on the gauge.
A sensor reading of 500 ohms or more will result in a "zero" reading the gauge, or lower.
In boiling water (212 oF), a good sensor will read around 160 ohms.
For normal engine temps (190 or so), the sensor will be around 180 to 200 ohms.
The temperature sensor is usually towards the rear of the cylinder head (between the #2 and #3 spark plugs). If you disconnect its wire and use your DVM to measure the resistance to ground of the sensor, you should start out with 500 ohms or so for a cold engine, and reach 180 to 200 ohms when the engine is warmed up.
The gauges usually don't go bad, so if you have a temperature measurement issue, it's more likely either the sensor or the wiring. Or your engine really is under/overheating.
-Bryan
A sensor reading of 40 ohms or less will result in a full scale reading on the gauge.
A sensor reading of 500 ohms or more will result in a "zero" reading the gauge, or lower.
In boiling water (212 oF), a good sensor will read around 160 ohms.
For normal engine temps (190 or so), the sensor will be around 180 to 200 ohms.
The temperature sensor is usually towards the rear of the cylinder head (between the #2 and #3 spark plugs). If you disconnect its wire and use your DVM to measure the resistance to ground of the sensor, you should start out with 500 ohms or so for a cold engine, and reach 180 to 200 ohms when the engine is warmed up.
The gauges usually don't go bad, so if you have a temperature measurement issue, it's more likely either the sensor or the wiring. Or your engine really is under/overheating.
-Bryan