Water temperature gauge wiring questions

[bryantreams]

Ok folks first of all I hate to start a new thread to ask this but I've searched and searched and I'm still not clear on how to wire up the temp gauge.

I have a sensor in my intake that has a coil covered wire coming out and going to the dash which is what I thought went to the temp gauge but that doesn't seem to be the case. I have read that I'm supposed to have a sending unit in one of the heads with a wire going to the gauge however both heads are just plugged. I went and bought a duralast temperature switch (part number TU5) and plan on installing that when I install a new water pump (mine has play in the bearings), thermostat, and heater core (heater core was disconnected by p.o. and coolant in floor pad so I assume it's leaking) tomorrow but I have no idea what wire goes to it or how it connects. It has a little round prong that I've never seen before. This truck is new to me and the wiring harness in the engine bay is a mess.

I have read that you can test the gauge by disconnecting or grounding the temperature switch wire but I didnt want to jump in and start grounding random loose wires. And yes I plan on cleaning up all the random wiring, just trying to figure out if I want to replace the entire wiring harness or just clean up what I have.

[Dead Parrot]

IF the wire you have is the wire to the temp gauge, connecting it to ground will cause the gauge to peg out to the hot side with the ignition on. IF the gauge still works. Since you are not sure if you have the correct wire, instead of a direct short to ground, use a 12V bulb between the wire end and ground. If you have the temp gauge wire, the gauge should still have a large move to the hot range. If the bulb glows bright, you have some other wire. You can't really test for open circuit voltage as the temp gauge sending wire will show 12v with a voltmeter when not connected to a sending unit and ignition is on.

And yes, at least for a sbc, the temp sending unit is in one of the heads. On mine, the driver's side.

[PAPA KENT]

Chevrolet used several of the ports available for your temp sending unit.Some use the port on the drivers side of the intake,some use the head under the exhaust manifold and some use the rear of the head.My 76 truck uses the intake while my 74 el camino uses the rear of the pass.head.Are you using the stock gauge or aftermarket? If you are going to use a aftermarket gauge get a mech. gauge that has the cable hookup installed and stay with your intake port unless you desire a cleaner look then use another one.

Kent.

[bryantreams]

I failed to mention that it has an aftermarket gauge. The coil wound wire in the intake I was referring to was actually a capillary tube (just found out what that is) indicating that it is a mechanical gauge. Is it possible for the capillary tube to go bad? It has no visible damage. I'm considering just buying another gauge from the parts house for $20 which comes with the tube so I can diagnose the problem.

Thanks to dead parrot and Kent for the replies. Sorry I'm such an amateur, learning as I go haha.

[PAPA KENT]

Yes it is a capillary tube.New gauges are inexpensive to buy and you don't want to take a chance on a bad one or a inaccurate one when it comes to engine temps.If the capillary tube is disconnected from your present gauge replace it.Seems the best insurance is generally the inexpensive parts that we have a habit of putting off.

Kent.

[bryantreams]

Well folks, I'm stumped. New mechanical gauge and tube...still doesn't even move a millimeter.

Here's a list of what I know about the cooling system:
New 180° mr.gasket thermostat
New mechanical temp gauge
Topped off coolant
Clutchless flex fan
Has an engine warmer on the lower radiator hose.

Any ideas? Even if the thermostat was stuck open it should get a little warm, right?

[monte0185]

Need pics of where its hooked up.. May have a blocked water passage of something. Could even be hooked up in the wrong location. Take some pics and post them so we can help better.

[bryantreams]

It's hooked up on the front of the intake next to the thermostat housing. I know for sure there's coolant in there because when I changed the thermostat And gauge tube a bit came out. Going to test the gauges in some boiling water and go from there.

[Axle]

Did the capillary tube get kinked at all? If so, its a paper weight now. Even if you straightened it back out, it probably cracked and let the magic gas out.

You didn't disassemble the tube from the gauge or sender did you? If so, it is again a paper weight now.

If thats all a negative, have you got an electric kettle? Take it out to the truck, put the sender in the kettle and watch. Or just boil water and bring it out. You should have movement then. If not, guage was no good to start with.

Alex.

[mrolds88]

Bryan, there should be a green wire that is long enough to reach the plug in the driver side head between #1 and #3 cylinder. the terminal has a wide slot on the wide side of the terminal that slips over that nub on the temp sender. This is the one you need to test to see if the gauge in the dash works.