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Old 03-17-2013, 01:34 PM
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Temp. Sending unit, Vs. Gauge

My temp gauge and the sending unit do not read the same as the IR at various points on the engine.

The rad and manifold and the electric fan switch are +/- a few degrees.
The problem is the gauge in the dash is reading about 30* higher than everything else.
These are aftermarket gauges with no name !!

How do I go about calibrating the sending unit with the gauge?

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Old 03-17-2013, 02:57 PM
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how hot

Let's first assume the dash gauge is reading the correct temp.
Now look at where the sender is located on the engine. It may be reading the coolant temperature in a hotter location on the engine such as just before the coolant leaves the engine and goes to the radiator.
Then observe the other sensor locations and make a comparison.
The gauge/sender combination can be tested for accuracy but I doubt that the dash gauge can be calibrated. It my be possible to add resistance in the wire that connects the sender to the gauge and get better result. That would be an experiment.
Also check this. The engine thermostat rating (say 180*) needs to be rated at lower temperature that the fan controller (say 190*). You don't want the fan to run until the thermostat is fully open.
This could confuse the dash gauge.

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Old 03-17-2013, 04:30 PM
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Thanks Vic.
The switch is 195* to ground on a relay for the fan and the thermostsat is a 180* and it cycles as needed.
The sender for the gauge is in the intake next to the water outlet and the I. Red is not reading 50* difference like the dash gauge is showing. Just trying to fine tune the insturments
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Old 03-17-2013, 08:38 PM
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?

What do mean by I?
Or RED?

vicrod
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Old 03-17-2013, 10:25 PM
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Inferred thermometer, digital
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Old 03-18-2013, 12:52 AM
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Sounds like you need a better dash gauge. I know of no practical way of calibrating the gauge that wouldn't also effect the reading at other temps, but maybe someone has info to the contrary. But I would still lean heavily towards a better gauge to begin with. If originality is an issue, there are companies who will regauge the stock unit.

If the temp gauge is electrical be sure the impedance matches between the gauge and sender.
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Old 03-18-2013, 10:06 AM
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Also need to make sure the engine is grounded to the frame and body properly.

a bad ground will produce high reading on an elec temp gauge.
will produce low readings on oil.

The gauges are pretty sensitive to incoming voltage and grounds.

Low voltages or bad grounds will affect the resistance of the sending unit.
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Old 03-18-2013, 12:24 PM
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The gauge is a quad set and the sending units were part of the kit.
The company has since gone out of business.... so I guess I will work on checking the engine to frame to battery continuity.
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Old 03-18-2013, 01:46 PM
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Also check the hex of the sender to the engine block or intake.
Too much sealant on the threads will cause an issue as well.

Just enough sealeant to seal, but little enough the threads can still get metal to metal contact.
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Old 03-18-2013, 02:40 PM
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I've seen teflon tape on a sender so thick it insulated it. Not good...
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