Three most useful gauges?

[Ptero]

The question was what are the three most useful gauges. You need a gauge to verify that you need to replace your 7-year-old battery? I use a load tester for that but I keep it in my tool box.

Also, the bird is not a yaw string. It conveys a lot more useful information.

I used to be gauge-happy. I had so many gauges on my XJ12 that I had to buy a dual-needle exhaust temp gauge because I ran out of holes. I'm a big fan of large tachometers and a fanatic for big pyrometers on big diesel engines. But those are all for performance applications. For economy purposes, if I were going to give you just one of all I've used over the years, I'd give you the bird. The bird rocks!

[RH77]

Originally Posted by Ptero

You need a gauge to verify that you need to replace your 7-year-old battery? I use a load tester for that but I keep it in my tool box. Also, the bird is not a yaw string. It conveys a lot more information.

Well, I use a "yaw string" more for severe Weather reporting, but the longevity of a battery is not mutually exclusive. I've had some that have lasted 2 years under normal conditions, and this one, which starts the vehicle at 100F or -10F and is pushing the 7-year mark under severe conditions.

The odd part -- I engine-off coast and run the headlights, ventilation blower, and sometimes the rear window defrost under batt only. So far all I've noticed an A/C-like draw from time-to-time, which I suspect is the alternator. I have a multimeter, but it reads the voltage as 12.5V+ across the terminals when cold, and 14.1V+ when operational.

My fear is a failing batt with an overworked alt, but how do I make that conclusion?

RH77

[Ptero]

Use a load tester. It's a metal box with a resistance circuit. You hook it up to your battery terminals and close the circuit. That enables a serious draw across a heater element. The needle on the gauge of the load tester will slowly drop as your battery charge falls off over ten seconds. If your battery cannot deliver a sufficient flow of electrons, the instrument will indicate that your battery is in need of replacement.

A tired battery will register 12.5 volts - the same as a strong battery - but it will fall off more quickly under load. A tired battery will also register 13-15 volts under charge from a healthy alternator but it will make the alternator work harder because as batteries age, sulfate flakes off the plates and creates a growing internal resistance. Older batteries do not stand up to the vibration of mobile applications as well as new batteries. I replace my mobile batteries after 3 years at most and use them for stationary applications if they are still strong.

BTW, when you coast engine off, if you are not on the accessory position but rather return to the ignition position to run accessory electrical systems after the engine quits, you are also energizing your alternator and coil, which is a boo-boo. A bigger boo-boo would be to accidently lock your steering column while futzing around.

[RH77]

I assume the "big box" auto parts places have the load tester device? I've helped replace batts on many other vehicles than my own where they test the load potential and the alternator production. I guess I let stuff like that go until it fails under normal conditions.

To save the alternator, I suppose it would be a good investment to have the test performed -- especially before Winter sets-in. I can say this, however: I let the batt go to slightly under 10V during a long period of drain while at a volunteer event this past summer. It would always start at 10-11V, charge to 14V or better at idle, and then shut it down and drain to 10V or less instead of idling. This occurred about 4-5 times this past year (storm spotting, with windows up and wipers/rear defrost running + ~100 Watt Radio transmission). I guess I'm optimistic that the batt is abnormally resilient...

RH77

Originally Posted by Ptero

Use a load tester. It's a metal box with a resistance circuit. You hook it up to your battery terminals and close the circuit. That enables a serious draw across a heater element. The needle on the gauge of the load tester will slowly drop as your battery charge falls off over ten seconds. If your battery cannot deliver a sufficient flow of electrons, the instrument will indicate that your battery is in need of replacement.

[Ptero]

That won't hurt it. You've got to run it down to 6-8 volts for permenant damage to set in. But if you do that a lot, and it sounds like you do, you should go to a dual battery system with a cheap solid state controller that isolates your (new) starting battery and runs your accessories off the old one (if it's worth keeping). That way, you never get stuck with a dead battery and you can always charge up the secondary battery. I would consider a small Optima glass mat for my primary battery. They are small, light and powerful and capable of deeper discharge than conventional lead acids. And you can sometimes get two into a space made for a larger battery. They're expensive, though.

[metroschultz]

After you get the new battery in you can desulfate the old one before you use it as your accessory bat.
Sears and many other stores sell a desulfating charger or you can ask an independent garage if they can/will do it for you. They will probably want 10 or 20 dollars for the job.
S.