When my truck was new, the coolant gauge used to go halfway up when the truck was fully warmed up. Then, a few years ago, it would stop about 1/3 the way up when fully warm. I changed the thermostat, and coolant sending unit for the gauge, with no change in the gauge reading.

To test the receiver gauge, the FSM instructs you to disconnect the connector to the coolant temp sending unit. Then you put a 3.4w 12v test light on the electrical connector to the sending unit, then ground the test light to bypass the sending unit. A successful test will light up the test light and the gauge should move toward hot.

My gauge moved to hot, and my test light BLINKED. I accepted the test and figured that a blinking test light must be normal. I just figured that I would use the 1/3 point on my coolant gauge to be the new normal.

Fast forward to today. I was looking through some wiring diagrams (yes, I do these things for entertainment) and was trying to figure out what would cause a blinking test light. I can find nothing in the circuit that would cause the coolant circuit to blink. I am now wondering if this is supposed to blink, or is there something wrong with mine that is causing it to blink, and also causing my gauge to read 1/3 hot instead of 1/2 hot.

The blink is very steady, about 2 times per second. My multimeter shows it pulsing from 0 volts to battery voltage at a very steady 2 hertz. The regularity of the blinks makes me think that some type of electronic device is pulsing the voltage, but there are lights on the dash that receive the same source voltage, and they don't blink.

Anyone else ever do this test? Did your test light blink?

Mine is a '94 22re

 

According to this, the flashing light is normal. I still can't figure out why it flashes though.

http://vintage.mitchell1.com/PClubDa.../V2I815019.pdf
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Good catch.

The fuel gauge has an 80s-tech mechanical "switching voltage regulator." https://www.yotatech.com/forums/f116...luster-259564/ Now that I think about it, it would make sense that the ECT gauge would need the same regulated voltage (it might come from the same regulator, or a parallel one of the same design).

[I haven't tested this myself.]

 

Thanks! I assume this regulator must be in the gauge itself, that is why it does not show up on any wiring diagrams.

 

Have you cleaned the female connector going to the temp gauge with electrical cleaner .

Over the years they do corrode which can screw up your reading .

Or like some people put nonconductive thread sealer on the sending unit and wonder why it reads strange if at all.

 

It's not on any diagram for the fuel gauge, either. After all, it wouldn't be a shop-serviceable item.

But at least one courageous poster on this site took one apart, and even replaced it with a zener diode.

 

Yes the mechanical voltage regulator is built into the cluster. The test you performed indicates the gauge is working correctly. One common problem is the screw connections that connect the gauge to the soft circuit board. It is a good idea to break the screws loose and use some contact cleaner on them, and re tighten them. Years of thermal expansion can cause them to come loose and corrode, causing inaccurate gauge reading or erratic gauge operation.

 

Is there a seperate regulator for each gauge? Is is there one regulator for all gauges?

 

One regulator

 

This is good info. The temp gauge on my 91 pickup 22re goes to about 1/8th inch up from cold and stays steady. I thought it was weird that it would read low like that especially since an IR thermometer at various places in the engine compartment reads ~180 at operating temp.

My hood also steams when it rains.

Maybe I will look into it this weekend.

 

Let us know what you find.