Coolant Temp Gauge Issues

[Liberty]

Noticed last night my Coolant Temperature gauge was completely pegged way beyond H. The truck wasn't even hot enough to have the coolant rush into the overflow when I checked the cap, so I know the truck isn't overheating.

Today after a cold start the gauge read Cold as usual before rapidly going up in "temperature" while also wiggling and dancing all over the place.

Its almost acting like there is a short or loose connection, but I'm wondering if maybe it isn't just the sender.

[geezer#99]

If nothing rushed into the overflow or it didn't puke all over the place when you pulled the cap when hot, it's only one thing.
Your level is way too low.
How full is it cold when you pull the cap off?
It should be right full!

[Liberty]

Its all the way full, the engine just apparently hadn't had the chance to warm up enough to build pressure. I've overheated the engine before, so I know how this particular engine acts and smells when hot.

The heater also works perfectly, so that should rule out a few things.

[ray_mcavoy]

Take a look at the temp sender wire to make sure it hasn't melted on the exhaust or chafed on a sharp edge.

The temp gauge pegging beyond hot without the engine actually overheating could be due to a short to ground somewhere in the temperature sending unit circuit. And a sending unit wire that's only making intermittent contact with ground could be responsible for your observation of the gauge "wiggling and dancing all over the place."

[Bigstevex4]

if your thermostat is stuck shut the Eng.
could be hot as hell and rad cold.

[muncher]

My temp gauge does something similar. It normally reads just below half, which is normal, then suddenly started to rise to hot. I pulled over checked the engine, all good there. So I did the usual give it a whack trick. I tapped on the temp gauge a few times. Then after 4 or 5 taps the needle in the gauge went right back down to its normal position. Now when it starts to rise again I give it a tap and down it goes. So in my case its just a faulty connection. I think it could just be dry solder joints or a loose connection. This past month its been great no phantom temp readings.
Give it a tap see how you go.