My temp gauge and oil gauge are "pulsing" together in unison. They move up a bit and down a bit in a synchronized fashion every few seconds. My amp gauge reads 15 pretty much all the time, too. Would this be a sign of my alternator going south? Other ideas?

All feedback appreciated. Thanks.

Jeff

It's the car's heartbeat. Naw, just joking.

You're probably correct about the alternator or VR. I'd check 'em both out.

What year is your car? I'm planning on upgrading to an internally regulated alternator to bypass the mechanical one on my '73.

Sounds like the voltage regulator. Both water and temp measure the current going through the sensor resistor and are sensitive for varying voltage levels. You might be able to see the same effect in the fuel gauge, although to a lesser extent. If its the original mechanical regulator then you should be able to hear a clicking sound from the buildin relays every time the water and temp gauge vary.

Have you tried to measure the cars voltage supply yet? A cheap analog multimeter would be quite helpful as you can see the variance over time better than with a digital one. Voltage should not exceed 14.8V.

...Voltage should not exceed 14.8V.

But it should exceed 12V. The normal range is around 13-14VDC. Anything less than 12.5V indicates that the alternator or regulator is dead.

When you say the amp meter reads 15, do you mean +15 or -15?

Rythmic pulsing...

Diode(s) in alternator?

If blown you may be getting AC instead of DC.

DVOM will help to diagnose or bench test the alternator,(or go for an AVR test).

I'm having the same problem. I've even got the engine up to operating temperature, shut the engine off and then turned the ignition back on without starting the engine. The water temperature guage is then functioning and continues to fluctuate. That would rule out the voltage regulator associated with the alternator. I have a 72 240Z Service Manual published by Nissan which states that there is a voltage regulator built into the combined water temperature guage and oil pressure guage to compensate for thermal effect. Could this be causing the problem. If so is there a solution?

Yes, the pulsing can be caused by the gauge's internal regulator. There might be an adjustment you can access through a hole in the back of the gauge. If not, you can take the gauge apart and adjust the regulator. The regulator is a heater wire wrapped around a bi-metal spring. The heater wire is in series with the 2 gauges. The current draw for the gauges heats the spring and opens points that interrupt the power circuit for the gauges. When the spring cools a bit the points close and the cycle starts over. The idea is to regulate the voltage for the gauges to about 8 or 9 volts. There is no service info for the gauges in the manual so you will need to experiment with it to minimize the pulsing. After you get the pulsing reduced you might need to re-calibrate the gauges. There is an adjustment for each.

That's some good info beerman. I had wondered if they were tied together by the regulator. I think it might explain why my temperature gauge started reading lower after I swapped oil pressure senders recently. The new (used) pressure sender reads more correctly now but the temp gauge reads lower, but also more correctly, assuming that my 180 degree thermostat is working right. The new sender had 0.2 ohms initial resistance while the old tested at zero.

The old oil pressure sender looked aftermarket and the used replacement looked factory, for anyone looking to fix the fairly typical "zero" oil pressure indication at idle on their dash gauge.

Just some odd facts for anyone else digging in to their gauges.