Upgraded my alternator and now my temp gauge is reading way hot

[Newguy71]

I recently installed a new alternator. The new one is like a 63 amp, my previous one might have been around 40amp but I'm not sure that matters since it was still hooked up through the original voltage regulator. I disconnected the voltage regulator and shorted the wires together like it says to do in the many threads about doing such an upgrade. I then picked up one of those nice red batteries that cost a fortune. Since then, the truck runs fine and my battery gauge seems to be working good. It'll change based on my rpms so I assume it's working good. What has seemed to stop working correctly or at least the same as before is my temperature gauge. I'm running the 190°f thermostat. Before the upgrades, my temperature gauge would run up to hot and then drop a little above the middle once the thermostat opened up. After the upgrades, it runs past hot, then dropped a tad maybe but never gets back down past hot until I slow down to a stop. And even then it still sits higher than expected, roughly 3/4 of the scale. I pulled over several times on a 15 mile trip to check and make sure it wasn't really running hot. I am thinking it has to do with my alternator putting out a higher voltage and therefore changing how my temperature gauge reads?? Anyone else had this experience? Any input?

[custom10nut]

It sounds like your connection on the sending unit is corroded. Unhook the wire and clean both the connector and the pin it goes on. It will help to put some dielectric grease on both ends.

[Newguy71]

Alright I'll try that. I recently replaced the sending unit and the connection. Plus, it just happened with this new alternator and battery... but what you suggested couldn't hurt. My sending unit wire runs up and around and down from my heater core hose so the wire picks up a little heat there. Dunno if it's enough to affect the resistance reading at the sending unit.... it hasn't affected it in the past so I'm guessing it's not an issue. Thanks for the info. I really appreciate it.

[Steeveedee]

My take- your truck is running hot, and it's simply gotten worse, concomitant with the alternator change. Unless the gauge is toast, but we don't know that, yet, do we? Is it hot enough when warmed up that it feels like it is overheated, or does it just seem like the gauge says so? Make sure you have the fan belt tight enough!

That said-

Check the output voltage at your alternator. It should run at a minimum of 13.5 Volts with a charged battery and no accessories in use. It should not run above 14.5 Volts in this same condition. If it continues to increase voltage with engine RPM, there is a problem with the internal regulator. I'm assuming that you now have an integral voltage regulator, since you bypassed the old external voltage regulator. If the voltage output continues to increase, or is higher than 14.5 Volts at idle, this may drive the gauge to a higher reading.

[Newguy71]

It doesn't feel over heated but I really don't have the experience to make that call. I'll check the voltages next chance but last time I did it was 13.5 but that was with a weak/bad battery. How can I tell if it's running hot or not other than the gauge? When I feel the thermostat housing its hot but it feels like its in the 190 range... I'm thinking I should check the temp gauge resistor on the dash panel and see if it is still what it should be. I checked the gauge panel a couple months back and fixed any issues I saw. (I'm an electrical engineer Mon-Friday and I'm confident it's in good shape now). Separate from all this, what should the gauge read? What temp is in the middle and what temp is at the hot mark? Also, what thermostat do you guys run? I thought it should be 195... thanks for the reply!

[Newguy71]

I started it up and put it up to 1k rpm. The voltage at the battery started around 13.5 but steadily made its way up to 15.5 volts. So I'm thinking maybe the alternator I got is not internally regulated... I thought all modern alternators were related... I'm gonna try and find the paper work that came with it and see what it says.

[garyd1961]

Whatever you do, don't remove the battery cable with it running. I did that on my 442 Olds when I was younger and fried all the electronics including every bulb in the car that was on. Also don't drive it anymore until you have it fixed or you will over charge the battery.

[Newguy71]

Yea hopefully no damage has been done. I have a replacement external voltage regulator but I think I want to go with an internal voltage regulator. Thoughts? Which would be better?

[Steeveedee]

Originally Posted by Newguy71

Yea hopefully no damage has been done. I have a replacement external voltage regulator but I think I want to go with an internal voltage regulator. Thoughts? Which would be better?

Give us a snap of the alternator, showing the connector on top. I have a 63 Amp alternator on my '70 truck as a factory piece. There isn't any real advantage with an internal regulator beyond the reduction of parts that have to be installed on the assembly line. Each job takes about a minute. A reduction of one minute, times a few million trucks (and cars) probably saved the consumer...nothing, but saved GM some amount of millions.

[VetteVet]

This thread will help you convert to the internal regulated alternator.
The internal regulated alternator uses a solid state regulator which gives a more stable voltage output with greater reliability, more voltage at idle, no dimming of headlights and more current output.
http://67-72chevytrucks.com/vboard/s...d.php?t=417872

The higher voltage output means more current in the circuit with the same resistance.
This equates to less resistance in the same circuit than before, which translates to a possibility of a higher temperature reading. I would doubt that it is the main cause of the temp gauge reading higher, but who knows. The temperature gauge reads hotter with lower resistance from the sender, however the engine temperature will decrease the sender's resistance to ground, and also increase the reading.

I think most of these small blocks should run a 180 degree thermostat. JMO