Just got my truck back from the shop, now $1150 poorer but with a new radiator, heater core, intake manifold gasket, valve cover gaskets, tune-up, 02 sensor, freeze plug, t-stat gasket, probably forgot something there. Anyway, the temp gauge was not working when I left. It worked, but only came to the first line, the truck had heat so I knew that could not be correct. They put in a new sending unit for free, figuring it went bad somehow when the intake was taken off. Works fine now, but now the gauge runs at about halfway, around the "o," when it used to run about 1/3 of the way, to the "n". Like I said, it's a new radiator. The truck seems to be running as cool as a cucumber, the hoses aren't real hard. They are not really soft either, they seem to be pressurized, but I can squeeze them together, and they are not even hot enough to cause any discomfort whatsoever when touching them. The air coming off the engine is cool. It is about 50 degrees outside. I also noticed that the gauge, just like the old one, constantly fluctuates about 1/8 up and down. One minute it is at the "n," the next it is at the "o." The old one did the same thing, just lower down the gauge. I know what you all are going to say, that the gauge sucks and to get a good one. But first, can anyone explain my symptoms, and second, if I attach a gauge to see what the temp really is, can I just attach it to the stock sending unit? It looks like just one lead on the sending unit, I'm guessing that I would attach it to the sending unit and that there would be a ground wire???

 

As for attaching a different gauge to it, I would go with one that has a capilarity wire sensor on it. These guages tend to be more accuracte in my experience because the reading is based on direct thermal conductivity through the bulb (sensor that threads into the block) then through the capilarity wire to the guage itself. The gauge responds to actual thermal changes not electrical resistance changes. Factory guage relys on the sensor to change resistance values based on temperature. (Everyone knows that eletrical components change their resistance values as they age. Especially if they are exposed to extreme temperatur changes). The other guage is actually responding to the thermal change right there in the back of the guage. Not unlike a thermometer would.

This type of guage is readily available and is easily recognized by the long length of bare copper wire surrounded by a spring coil over its entire length. The bulb threads into the same location as the existing temp. sensor. If you want to run both guages, some manufacturers supply or have available an adaptor that allows both sensors to be installed together.

 

"Everyone knows that eletrical components change their resistance values as they age. Especially if they are exposed to extreme temperatur changes" Actually, I didn't. Does this explain the new gauge as showing the engine to be "hotter," when in fact it seems to be physically cooler, or at least, the same? Does the degradation of the resistor cause the gauge the read colder?

 

Why not run an inexpensive set of mechanical oil pressure and engine temperature gauges and eliminate those concerns?