Installing temp guage sensor(aftermarket)

'71 Dart Custom said
Ok, I'll try to say this without writing a book. 2yrs ago when I bought the car both gauges worked intermittently but I thought the temp was reading low, not even registering hardly. Then, after killing the motor the temp gauge would slowly begin to rise almost to halfway mark. Bought the trio gauges and finally went the pipe fitting route, but was never satisfied with the results. The new gauge starts at 130 degrees and just like the old one, when I'm driving, it doesn't register at all. I kill it and come back 15 minutes later and it's reading 170-190.
So, last weekend (2yrs later) I decided since the new gauge reads like the old, why not get a new orig sensor and just try to fix the old gauge. But now the factory gauge is completely dead, I tried grounding the wire going to the sensor, but nothing. Shouldn't that peg the needle if it's working? My gas gauge is still working just like it always has. I would rather fix the factory gauge, but I've never even pulled the gauges out of the dash, and won't until I know what I'm looking for. Also, all this makes me wonder if my engine is even warming up to normal operating temp? The heater doesn't blow very hot.
And why is it heating up after I kill it? I understand that heat rises and the sensor is at the top of the motor, but I've never noticed one heat up that much after shutdown.
One other thing, when it sets and gets hot like that, it's hard to crank and the lifters clatter if I put any strain on the motor. It doesn't seem to run good hot.
Sorry, I'm no good at diagnosing. I'm one of them "tell me what's wrong and I'll do the labor" types. Thanks for all the input.

Hmmmm.....quite a bit to comment on here....I think I would start by putting a good live gauge on the oil pressure to see what that looks like. If it's low at operating temperature, there is no use going any further with anything else. If it's good, install a new 180 degree thermostat ( I suspect you don't have one) and see if the temp gauge (either one) works now. You may need a new cam and lifters if they clatter and you have good oil pressure. Also check the rockers and push rods for wear.
As you have done already, you can test the factory gauges by connecting the sending unit wire directly to ground and then turning on the ignition for a second or two to see if the gauge comes up. If not, there could be many reasons, from sender to wiring to circuit board to the gauge itself. Those instrument clusters are not too bad to pull. I like testing them out of the car. That way you can test several things at the same time. I've had many of those clusters with just bad connections on the circuit board. Loose nuts or a bit of corrosion and the gauge won't get a good connection. A simple icepick test light and a couple of jumper wires is all you need to McGiver a test bench. Same with the fuel sender. With it out of the car (very important!!! Do not do this with the sender in the tank!!!!) connect 12 volts to the sender connection and then connect your test light wire to the battery ground and the pick end to any part of the sender housing. The light should come on and get brighter or dimmer as you raise or lower the float arm. If it doesn't light up, the sender is bad. Sometimes you can fix them but new ones aren't too bad in price. That should keep you busy for a while... :toothy7:
Let us know your progress.