Pre-war (up to 1942) 1940 Lasalle electrical

[Ben Medlock]

Getting this car on the road finally and finding an issue with the temp gauge. Its pegging out hot but I know its not because I have a modern temp gauge installed right next to the cars sending unit. I've noticed the gauge rises when the engine is reved then drops back at an idle. Also noticed when I turn on lights that the temp gauge drops. Checked the generator with amp meter and it shows around 8.7 at an idle then jumps to 12 when the engine is reved up. I'm thinking voltage regulator but looking for another opinion before buying another voltage regulator.

Thoughts and advice is appreciated.

Thanks

[Jay Friedman]

A 1940 Lasalle should not have 12 volts showing when the engine is revved up, nor 8.7 volts at idle. It's a 6 volt system and might show 7 or 7.5 volts when the engine is revved up and the battery is fully charged. Has it been converted to a 12 volt system?

The stock temp gauge is electrical and I think it works the same way as a voltmeter.  That might explain what you are seeing.  Something not right here.

Question: is the modern temp gauge you have installed right next to the sending unit mechanical or electrical?

[Ben Medlock]

It's a mechanical thermostat. Way back when I started on this car it had been converted to 12v but thought I had it all converted back. The motor I put back in it was not the one that came out. Is it possible I have a 12v generator?

[39LaSalleDriver]

I've had a similar issue off and on over the years. I've never figured it out, but I'm convinced there is some feedback that comes through the wiring from the voltage regulator to the temperature gauge. I say this because on occasion I have observed the ammeter shoots pretty high and stays to the "C" while at the same time the temperature pegs up to "HOT". If I get out and rap against the voltage regulator cover, they both drop down to their normal, as expected readings. If I swap out the voltage regulator, the problem goes away...for a while, but invariably it returns some months later.

I spent a whole summer chasing an overheating problem that I now don't really think existed other than this glitch.

If anyone has any ideas what may be going on, I for one would be all ears.

[Ben Medlock]

Hmmmm. So, regarding my generator, is it possible it is a 12V generator since I'm checking 12V with a volt meter? Or, are all generators the same? I'm a lot better with mechanical issues than electrical. These 6V positive ground systems have always baffled me. Does the power from the generator go through the voltage "regulator" to get regulated down to 6V or.... what?

[Jay Friedman]

Hmmmm. So, regarding my generator, is it possible it is a 12V generator since I'm checking 12V with a volt meter? Or, are all generators the same? I'm a lot better with mechanical issues than electrical. These 6V positive ground systems have always baffled me. Does the power from the generator go through the voltage "regulator" to get regulated down to 6V or.... what?

The power from the generator goes through the voltage regulator to get regulated.  But not "down to 6 volts".  Both the generator and the regulator must be the same voltage and also the same amperage.  As the car rolls along, regulators reduce the amperage output when the battery is fully charged to prevent the battery from being overcharged.  They increase the amperage output when accessories such as the lights are turned on so that the lights don't drain the battery. 

All generators are not the same.  As far as Cadillacs are concerned they are 6 volts until 1952.  Depending on the model year, they vary in the maximum amperage output.  Beginning in '53 they are 12 volts.