Starter + glow Voltage loading.. need comparison figures.

[redbaronph123]

I need some help for comparison.

Last night, after driving under the rain, with all lights on, AC on, Aux fan on, radio on, my car wouldnt start after I parked in a supermarket. Checked the voltage of my battery and it showed only 11.9V (non-running condition). (I knew that I'd have a problem when I could see some faint light on the battery indicator). (By the way, had the battery tested at a batt shop, and they say my alt is charging properly, and the batt was load tested, and at 200AMP(?) load, the batt went down to 10V which they say was just fine - is it?)

Anyway, got it started... got home.. and let the engine run. After 15 minutes, the car is running with a 13.3V reading on the battery, with all accessories off. Turned on AC, the V drops to 12.8, with all lights turned on, the V drops to 12.5V.

This morning I tested how much drain my starter puts in my car. Hooked up my V-meter, 12.2V. Turned ignitino to glow, 11.5 - 11.6V, waited for glow to end, 12.2V, started car, V drops to 10.3V.

Should it drop this low? As it is, the started turned (of which i think is quite slow), but managed to get the car started. I didnt get to test the amperage, as I do not know how.

Should the V drop this low?? around 10V? will that still be able to start the car? (well it does, but am i playing with fate, that one night, just like last night, my car would simply be too stubborn to start).

Battery is Outlast brand (maintenance free) 20 months warranty, and on it's 15 month. Should I just replace it?

Maybe someone can conduct the same simple test and verify if my readings are at par or not.

Car is a 1979 300TD, series plugs, bad timer relay. Glows for about 15-20 seconds, as verified by V changes when glowplug stops.

[dkveuro]

You need to test the charging ampage.
Unless battery is fully charged to 12.65 vdc it is under charged.
Running voltage should be between 13.5 vdc and 14.2 vdc.

In wet weather it is not unknown for the alternator belt to slip and you loose charging but usually not low enough to bring on the charging lamp.

minimum voltage while cranking should never fall below 10.5vdc.
It may be you need a 800 amp or better battery.

Cheap batteries a waste of money especially on a diesel.

Diesel engine relies on speed of cranking to heat up the compressed air to 900f
to light off the fuel...slow cranking will not compress air fast enough to raise temerature to ignition point even with glow plugs working.