Fuso glowplug operation

[kerry]

As you may have noticed from my plethora of threads on electrical issues, I've been chasing some down on my 99 FG. Related to that problem is a question which I put to the parts man at the Fuso dealer today. Didn't get a satifactory answer.
When do the glow plugs operate on a 99 FG? I've only had the glowplug light come on at temperatures under 40 degrees but I've noticed a currently draw on the battery when I start the truck in the morning, even when it's 90 degrees out. The parts man said the glow plugs turn on whenever the engine block is below XXX in temperature and could be expected to operate most mornings. He also said they turn back on when the engine is idling if the engine is not hot enough. He could not explain to me why my glowplug light does not come on even when I know there is a current draw with the first start of the day (perhaps other times also). The current draw goes away when I hear a relay click which I believe is under the left front dash. Any insights? Is the glowplug light triggered by temperature independently of the actual operation of the glowplugs?

By the way, I'm inquiring about this topic because I'm considering the hypothesis that my relatively new batteries failed because I had a glow plug relay stuck on. I have yet to test that hypothesis. I believe the glow plug relay is the relay on the starter closest to the frame rail.

 

[FusoFG]

I think that relay click that you hear is normal. Mine has done it every time I start my FG for the last 16 years and I haven't had any battery problems, at least not since I switched from Gel cells to Optima AGM batteries.

I originally installed Gel cell batteries inside the camper because I wanted protection from explosion.

But Gel cells need a special lower charge voltage than either standard flooded cell or AGM batteries and I went through 3 sets of 4 batteries in the first year before changing to Optima AGM. All the Gel cells were replaced under warranty eventhough I was charging with excessive voltage.

I've only had 1 set of red top Optimas and 1 set of yellow top Optimas in the last 15 years.

There is another relay that clicks off once the coolant reaches normal temperature.

You mentioned a hot battery. That's either excessive current draw or over charging. Maybe the regulator in the alternator is bad? Excessive charging might be indicated by abnormal wear on the alternator brushes.

My glow plug light only comes on when it's very cold. I'm not sure what temperature, but it only happens a few days a year here in GA at 2500 ft. In the 20's I think.

You should be able to tell when the glow plugs are on by measuring to ground the voltage on the buss that runs from glow plug to glow plug.

I'm not sure what all the relays do but they appear to have something to do with engine warm up, exhaust brake during warm up and idle speed increase during warm up.

I usually turn the key on and wait for that first relay to click before starting. It always starts instantly.

Do you have the engine warm up switch on?

I always used the warm up switch, but a mechanic in Tampa, FL told me I didn't have use it once the engine was warm.

Certainly you could have a problem with the alternator, regulator, relays, sensors, corrosion, wiring (I've had mice make a home in the dash and eat the insulation off wires shorting out the dash light dimmer) but you might look closely at any modifications made during the installation of the original service body. My experience with upfitters adding body lights, pto's, brake lights, etc is pretty disappointing.

Do you have the workshop manuals?

 

[kerry]

Yes, I have the manual. Relay is clicking and I don't have the warm up switch on. There's a .335 amp draw on the battery with nothing on so the problem could simply be a matter of the batteries going dead after sitting connected for 5 months and one of the batteries not recovering from this discharge and slowly destroying the one remaining good battery. This is the likely scenario, but I'm considering other hypotheses also.
I'm not overcharging. Voltage at my cigarette lighter digital voltmeter has never shown above 14.5 volts.
The single 850 CCA battery I currently have in place instead of the dual batteries seems to be working fine.
Yes, I will eventually get around to actually checking the voltage at the glow plug relay to confirm or deny what the guy at the dealership told me. He may have had newer FG's in mind, rather than my 99. He didn't know that my 99 glow plug relay was mounted on the starter, for instance.