Hi -

I have a 1994.5 F-350 (PSD), and notice that after starting, the voltage gauge stays around 9 volts, then after 45 seconds or so, the voltage gauge shoots up to normal. The lights on the dash also confirm this voltage change. Is this normal, or a precursor to something going out?

Thanks in advance!

Mike

 

I think its the glow plug staying on. I have read about recently and sound normal.

 

Mike, this is normal for the later model PSDs.

The charge output of the alternator goes up in two steps. When you first start the truck, it's on a low charge, then after maybe a minute (almost two minutes on my truck) and depending on temperature, the high, or normal charge rate kicks in.

Your dash meter is probably inaccurate, a good digital meter across the battery would read maybe 12.5 to 13 volts on low right after you start it, then it'll jump up to 13.8 to 14.5 volts.
If you could read charging amps, low might be only 2 to 5 amps, then the full 100+ amps becomes available after the waiting period.

I haven't seen a good explanation why the trucks are set up this way, my guess it that it's to protect the glow plugs from a big voltage surge right after a cold start.

When my truck had only maybe 6,000 miles on it, the alternator failed and only put out the low charging rate. Eventually the batteries ran down and no start.

If you are noticing the lights get brighter or dimmer depending on the charge rate, that might be telling you that your batteries are on their way out. The alternator is probably OK and doing what it's supposed to be doing, but your batteries aren't holding up on their end. Until the alternator kicks into high gear, your truck is running 100% off of the batteries. You should check all of this with an accurate digital meter.