Temp Gauge Not Working

[rally]

I've never repaired one of these and am not really sure where to start checking for any problems.

I have the gauge in the dash, but it doesn't work. I'm running a 350. Anybody know how to troubleshoot one of these? I'm hoping the problem is not the gauge and that it's just not connected or something, but not sure where to start.

[demian5]

First, pull the wire off the sensor, turn the ignition on and ground the wire to the engine. If the needle pegs, its a bad sender. If it does nothing, it could be a circuit board, gauge or the wire itself.

Get a wiring diagram.

[rally]

Ok, thanks demian5. I'll give that a shot.

[custom10nut]

Do as Damian says, and then clean you contacts. They like to get corrosion it them

[special-K]

First of all, tell us what it's doing. Is the needle pegged on H or lame at C? If it's pegged it is grounded out somewhere and if it is lame it's no power

[VetteVet]

The temperature gauge is one of the easiest to troubleshoot. Follow the instructions above and if the gauge goes to full hot then it is probably the sending unit has went bad. It is based on resistance to ground and is controlled by the temperature of the coolant in the engine.

As the engine coolant heats up the sender resistance goes lower and the path to ground resistance is reduced. This lowers the resistance on the sending unit wire to the gauge and the gauge reads hotter.

This explains why directly grounding the wire to the engine block makes the gauge go full hot or more.

The sending wire runs directly to the cluster plug on the back of the cluster. It will be the green wire on pin 6 of the plug and it will then go to the sender side of the gauge as shown by the diagram below.

The power side of the gauge comes off the fuel gauge when the key is on and
it is shown by the purple wire on the diagram. These are actually the copper strips in the cluster panel but they are easy to follow.



You must have a good ground on the cluster panel to the cab for the gauges and lights to work so if the instrument lights work then the cluster is grounded. Each gauge must be grounded separately also. The grounding lug should be evident on the gauge.

If you see nothing from the gauge on the test you could have a break in the sending wire or a poor connection on the firewall block where it goes into the cab by the master cylinder. There may not be any power on the gauge on the
power side of the gauge because the copper strip may be broken or the gauge resistor may be bad.

Here's a picture of one of my clusters with the gauge installed.



If you look at the hole where the cluster plug goes in, on the left end lower row is the no. 6 pin copper strip runs to the sending side of the temp gauge and the right side of the fuel gauge feeds the power to the right side of the temp gauge.

[el_fantasma]

This will make you guys laugh. My temperature gauge never moved highway, sitting in traffic whatever. Turned out the thermostat was missing. Put one in and now temperature gauge works normally.

[MagmaJct]

Originally Posted by el_fantasma

This will make you guys laugh. My temperature gauge never moved highway, sitting in traffic whatever. Turned out the thermostat was missing. Put one in and now temperature gauge works normally.

I 2nd that. My late uncle must've put a 160* thermostat in mine. Gauge wouldn't work. Put a 190* in, and it has worked ever since!

[rally]

Thanks for the info guys. I had a chance to test it today. The needle sits lame under C and doesn't move at all at operating temp. I pulled the wire from the sender today and grounded it on the alternator and it pegged out. So the gauge seems to be good. There's definitely some corrosion on the connector, though, so I'll clean it up and see if maybe it just wasn't connecting properly.

But in the meantime I'm also looking around for another sending unit in case it really is bad, but I'm noticing a few different product numbers that say they'll fit a 350: TS76, TS 11, etc. Anybody know which sending unit is the right one? I haven't pulled mine to see which one I'm currently running because I wasn't sure if it's going to dump coolant or anything when I pull the unit. My drain pans are full and waiting for an oil pickup.

Thanks again for the help, everyone.

[67 chevelle]

There are at least 3 different types used on a 69 c10 with a 350 engine

http://www.rockauto.com/en/catalog/c...+/+sensor,4748

[Green Monster]

After chasing other culprits with no improvement, a temperature sending unit with correct resistance from Letriclimited.com addressed the false (determined by hand held infrared thermometer pointed at thermostat housing) hot reading in my 72 Blazer temp guage. It's been 4 years since installation and and then sending unit works great.