I've got a strange situation that I'm not sure what to do with.

I had a Bosch temp gauge that stopped working a week or so ago and I stopped in at an autozone to grab a quick replacement. I threw in a new Equus gauge and it seemed to work just fine. Less than a week later that gauge started reading really low and then just quit altogether.

To verify it actually went bad (because I found it hard to believe) I boiled some water and put the sensor in the cup and nothing happened. I also checked the intake temp with a laser temp gun and it was hot enough to register on the gauge. It was about operating temp, 180-ish. So, I'll be taking that gauge back for a refund but in the meantime, I'm slightly concerned about why two gauges when bad inside of one week.

Is there something I should be investigating here?

 

Most electronic temp gauges use the ground of the engine to operate the resistance. How did you test it? Did you ground it? The most possible issue is that you have a failing ground on your block. Grab a ohm meter and test the ground at the sensor.

 

That's a good thought.... But I'm not sure it's an electric gauge. It's just got one "wire" coming off the back that plugs into the port in my intake coolant path. The readout is just a needle, not an 7 segment LED.... Am I understanding this correctly?

The new one was tested by just plugging it into the port like the previous one. No wiring was done.

 

if it has a “wire” it is electronic. If it has a metal tube or hose, it is analog. So the one wire tests resistance between the ground and the element. So you need a good ground. Usually the water/coolant pulls this off with a good ground somewhere else but when they rust, they get bad. So test the resistance of the water neck to the negative battery terminal.

 

Could you post part numbers of the gauges you got so we can look them up to see how that should be installed.
But what Pcmdub said is right and you would of needed to send power to the gauge for it to work.
Dave ----

 

Interesting.... how does a device measure the difference between two points if it's only attached to one point? Apparently, I have some learning to do. I'm assuming right now it's a mechanic gauge and according to what I read today about mechanical temp gauges, it appears that the "wire" going to the intake manifold is actually a capillary which makes sense. It's basically working like a mercury gauge. It also explains why I had a low reading before it stopped working. I assume the capillary was partially pinched or damaged.

Assuming it's just a capillary with some heat reactive fluid inside then I have to assume I've kinked the line or damaged it beyond use somewhere... Which can easily happen fiddling around in the engine bay or under the dash.... Both I've been doing all week. With that I'm mind, I think I'll throw the mechanical gauge out as it looks like I'm the problem, not the device, and buy an electronic one which will definitely take more abuse, as long as it's an RTD and not another mechanical gauge that's converting capillary pressure to a readout. That would result in the same problem (me damaging it).

The original cluster panel on this old truck has a temp gauge that's electric but it was never used because the wiring was chewed up. Might just run new wire and get the RTD nipple for the intake manifold and see if that works. If so I'd rather use that and not some aftermarket unit.

Thanks for the advice. I'll update tonight sometime.

 

Automotive electronics are odd that way. You never have run a "ground" wire as long as the chassis, body, and engine are grounded. So the one wire you have from an electronic gauge is testing the resistance of the temp sensor against the other wire (ground of the engine/manifold).
https://www.aa1car.com/library/coolant_sensors.htm

 

Certainly if the gauge is grounded mechanically it can operate on one wire because you still have two points. But this after market gauge isn't that type.

I did get time to dig into this over the weekend and I got the OEM instrument cluster gauge working. In the process I nearly fried it 😟😬. I didn't realize they were 6 volt and had the source voltage passed through a voltage regulator. I tested it 12v to ground and it went to HOT really fast and smoked just a second. I relanded the source to the 6v regulator and purchased a few RTD nipples and tested the resistance of them in some hot water and verified with a kitchen thermometer.

What I also noticed was that the water temp at the thermostat housing was hotter than the temp at the intake crossover and I don't recall the location that was used on the original intake. My current intake is a cheap aluminum guy.