12v or 24v glow plugs...

To be, or not to be...

oh wait sorry... wrong phrase

anyway... I had a thought....

CUCV's have a resistor bank on the firewall for reducing the 24v to 12v for the glow plug system. This we done (in theory) to balance the load of the glow plug system accross both batteries. But in doing so, puts an extra wasted load on the batteries, right? I have found a source to buy 24 volt glow plugs and am thinking of getting rid of the resistor bank, and running them straight 24.

Anyone see a problem with this?

you could change out the connectors to the hmmwv round pin type and use hmmwv plugs!! everything on the hmmwv is true 24v

So would you agree, that I would be better off without the resistor bank? My source for 24v ones carries the ones with the flat prong in 24v I believe...

check this out http://www.ssdieselsupply.com/product_90_SSD_Glow_Plugs_for_24_Volt_Military_Vehicles.html

In my opinion a 24v set up just for the starter and glow plugs does not justify having it, why not place the electrical load evenly throughout the vehicle and on the batteries? Modern gear reduction 12v starters provide the same "if not more" cranking power and rpms. I like the idea of having plugs and controler/relay available at the local parts store.

You need to be real careful doing this! The glow plugs in the CUCV are designed for cold weather starting to meet arctic application requirements. When the Army first fielded the CUCV GM advised that the glow plugs in the CUCV were 12 volt plugs, where the commercial trucks had 6 volt plugs. This is a bit confusing so they don't advertise it a lot, but their explanation was that the way they're wired in the voltage to the plugs is correct.

The 24 volts to the glow plugs on a CUCV go through resistors so that the initial voltage to the glow plugs is higher and you get a quicker start, especially in cold weather. As the resistors heat up the resistance increases and voltage to the glow plugs drops (Ohm's Law) so that once the engine is running you only get enough voltage to cycle them on and off without overheating them.

If you bypass the resistors and run straight 24 volts you'll burn out the glow plugs, probably causing them to swell up and require pulling the injector, breaking off the tip and pulling it out of the chamber, then installing new glow plugs. The best plan is to install new glow plugs and run 12 volts to them. Go to http://www.roscommonequipmentcenter.com/news_notes/nn10.pdf for some good info on how to do this.

Read up on the glow plugs I was talking about. They are self limiting, and CAN'T burn out in that manner and swell.

The civvy plugs were 6 volt for faster heating. It was horrible design, constantly burning plugs out.


Installing new plugs and running 12volts to them in that manner is a bad idea. It pulls all the voltage from one battery. This is the other reason the military design is the way it is.

Also, please add your location to your forum profile. Its a requirement here... thanks

I'm very familiar with the glow plugs you mentioned. We (Army Tank-Automotive and Armaments Command) did a lot of testing on them and found some surprising results. You're absolutely correct that they're a vast improvement, though some brands (Bosch for instance) still swell enough to be a problem. Still nothing like the old days though. Even with the Bosch we've been able to wiggle and turn them enough to get them out of the hole and didn't need to pull the injector. To test them we just applied voltage to them until they failed. We did a variety of tests such as engine running and voltage all of the time, engine off and full voltage, etc. We didn't try putting excess voltage to them though since there's no reason to expect that in the field.

The link I referenced gets rid of the 24 volt side, equally balances the load on both batteries, and requires only one alternator. We developed this method for the fire departments and other agencies using excess CUCV's so that they didn't have to mess with the logisitcs issues of the 12/24V system. The single alternator works great in most cases, but where they do a lot of winching, running power hose reels, etc. we recommend that they go to a DELCO 27SI alternator - bolts right up.

On the location, I don't think that's a requirement anymore (I just checked and the page lists it as optional). It's no big deal at the moment, though in my job it sometimes is. For instance, I just returned from a year in Mosul, Iraq and spent 2 years working in the embassy in Cairo, Egypt before that. Those are history, so no big deal on a public forum, but where I'm at at a given time isn't always the best thing to advertise. I'm in the Pacific Northwest right now.

your link converts the whole truck, and I need to keep 24v for my winch


and use the location is required. I have had a hard time getting the form to make it not list it as optional. Please add it as per the FAQ's Even your 'home state' is fine. I understand you are on the move, but I am sure you are based out of somewhere.

Should be good to go now.