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Old 11-19-2022, 09:07 PM   #1
the_hairy_baboon
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Default Coolant Temp Gauge - moves but not very far

1983 B21FT. Coolant Temp Gauge doesn't rise properly as far as I can tell. Coolant level is between markings on the bottle.

Keyed off the gauge will sit on the lower end, similar to fuel gauge. Keyed on, and after driving around for a while, it only advanced maybe 1/8th of total range, I assume ideal temp would sit somewhere around 50%.

Does it sound like the movement seen is purely a response to vehicle being keyed up, and that the oomph from the actual sensor doesn't come in (check sensor / wire to gauge), or that the gauge itself may have an issue and the sensor may be fine?

If someone has a bit of initial guidance as to which part to look at first (and any resistances / GreenBook numbers to pull from ozvolvo) that'd be helpful.
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Old 11-19-2022, 10:26 PM   #2
hiperfauto
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Here are the resistance figures for testing the sensor. A 100 ohm resistor installed in place of the sensor (one end to ground, the other to the yellow gauge wire) should make the gauge read in the middle if it's working properly.

http://hiperformanceautoservice.com/...enderSpecs.jpg
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Old 11-20-2022, 12:48 PM   #3
the_hairy_baboon
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Ok. Looking at my wiring diagram, I'm guessing the yellow wire from the sensor to the cluster is part of a bundle so it's not as simple as unplugging a single spade on cluster and trying a 100W resistor to ground there.

Looks like easiest will be to attempt to reach under and unplug the yellow wire from the sensor itself. Relative location on cylinder head block (http://turbobricks.org/forums/showpo...88&postcount=2)

I assume to remove it if it is dead I will need to drain coolant at least below a certain level. What's the best way of doing that / what size socket do I need for the sensor itself?
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Old 11-20-2022, 04:01 PM   #4
hiperfauto
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Connect the 100 ohm resistor at the sensor end of the wire.

If you leave the cooling system sealed it won't leak very much when you remove the sensor as long as the system isn't under pressure. If you have a replacement sensor to swap in then you don't need to drain the system. If the sensor is going to be out for a while then you may want to drain the system first.

Use a 17mm deep socket with a swivel and extension to remove the sensor. A shallow socket may not engage the hex properly because the terminal sticks out too far.
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Old 11-22-2022, 04:57 PM   #5
John242Ti
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You might also have some resistance in the wiring. My 242 also has this issue. Had it with its original engine, and with the current engine. The gauge did go up when the head gasket popped on the original engine and properly pegged itself as the coolant level dropped. When I installed the original engine into my 245, after replacing the head gasket, the gauge in that car read normally. Didn't read low. Read around 8:30 when fully warm, since I was using an 82 deg C t-stat, instead of a 92 deg C or 87 deg C t-stat. The 242's gauge usually sits around 8:00 when fully warm. Might hit 8:30 if I bomb up a hill in boost on most days, 8:45 if the ambient temperature is close to 100 deg F.
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