1973 Charger temp gauge

[73chargerdude]

Not sure if I put this in the right place.  Just joined the site.  I've owned my 73 Charger since 1979 and it always seems to have a problem, at least I think, with the temperature gauge always running towards the hot side and then it backs off to normal once it gets going again.   When I first start the engine the needle is at the C mark.  Takes a little driving to get it to the normal area.   When the engine gets started after it warms up, the needle has always shot to the H and then back down.   Cut to the chase.  A few years ago I had the motor rebuilt (they pulled out the stock radiator and put in a new one with a little more capacity) and put in a rally dash from a 71 Charger to replace my rally dash to get the tac I bought many years ago.   I experience the same thing with this temp gauge.   The coolant is fresh as is the oil.   I was sitting at a long long train crossing last week and when I thought the train wasn't going to end, I put the car in neutral.  Within a few minutes the gauge shot to H so I shut the car off.  Once the mile long train passed I fired up the car and the needle hung up there at the H position before slowly returning to the normal area once I got cruising again.  I'm thinking these gauges are utter crap and have always been that.  My alternator gauge needle is always moving, really fast ...like taking your index finger and wiggling it back and forth for lack of better words.   Is there hope for this or should I put on one of those Temp gauges and run it to the inside and mount it somewhere.   I know the thermostat works as I've had the top off of the radiator and watched the coolant flow when the engine warms up.   I was white knuckling it at the railroad crossing..don't want to experience that again.

thanks for any help or info on this.   

[400sforever]

I've got several of those cars and I've always thought the gauges were pretty accurate. When I had one getting hot, it was getting hot. Turned out to be a plugged radiator. May not be that case for you tho. Then I had another one get hot because I thought the radiator was good but it wasn't holding tight pressure. I've seen new radiators that weren't worth a crap! I've also seen sticky thermostats! Do you have a full fan shroud because that can make a big difference too? I'd say you alternator is no good or your voltage regulator is bad! Hope this helps

[73chargerdude]

Thanks for the info.  Everything was replaced when I had the motor rebuilt   Motor was a 400 now 406.   New Mopar heads, new radiator, belts, temp sensor, alternator, ballast, etc.   Only has about 1000 miles on it and has had a flush and fill just about 50 miles ago.   Converted it to EFI a year or so ago but that's not related to cooling that I'm aware of.  Before the rebuild with the original motor and radiator it would do similar things, so i'd run it w/more anti freeze to keep it cool.  stupid i know but it worked.

I might try one of those aftermarket temp gauges and run it into the cabin area and see what that reads.   i'd think the FAST EFI would have shut the motor down if it was over heating.  Though I should probably check on that.   

[ODZKing]

The temp sensor is basically a short to ground. In other words if you take the wire and touch it directly to the block you should get the gauge to read all the way up.
So what you may have a an intermittent short via a bare spot. And it won't jump but move gradually as that is the way the gauges work. Check the wire, which should run on the side of the valve cover btw, for any bare spots or cracks.  40 plus year old wires ... enough said.