6V or 12V glow plugs?

[914turboford]

I just put a 1983 6.2 in my 1985 GMC K10. It will not start. Probably not cranking fast enough but will try again in the morning with the battery charger on tonight. The replacement motor had what appear to be new glow plugs in it so I left most of them in. I did put in a couple of ones from the old ('85) engine. So, apparently, I have a mixture of old (12V,right?) and new
(6V, right?) GP's. I guess it won't cause a problem running the 12V GP's with the 6V system. But will they get hot enough to help start? I suppose I will have to change them all over to one or the other. I can smell diesel so I think I am injecting fuel. My timing is set to the mark (I am using the 85 pump on the 83 block, timing cover).
Brian

[88 K30]

Why do you think the plugs are rated differently? Was one engine originally from a CUCV (military)? It is my understanding that all regular civilian applications of the 6.2 glowplug (9G, 11G, 60G, etc..) were actually rated as 6V plugs, not 12V as one would think.

[gmctd]

Test each glow plug using your jumper cables connected to your battery - black lead to the body, red lead to the spade - each 'plug should glow to the tip within 5 seconds - any that glow center-only are not suitable for cold-starting - any that do not glow are not suitable for anything.

Caution - glow is hot, will sear thru flesh to the bone.

[914turboford]

My Hanes manual says 1984 and older used 12V glow plugs while 1985 and newer used 6V. The manual also says the 12V's should measure 1.8 ohms and the 6V .8 ohms, or maybe it is vice versa. I was planning on making a manual switch and sending 12V to them. Any problem with this if I have the earlier ones? If they really do run on 6V, where is the voltage stepped down? At the controller? BTW, I got it to start today. I had broken the OE controller so I jumped across it, sending 12V to the GP's, albeit for only 3 or 4 seconds. I don't relish removing any of my passenger side plugs, as I have a Banks turbo with a big fat exhaust pipe blocking access to them.

[ccatlett1984]

the difference with the different voltage ratings has nothing to do with the voltage that they are fed. the 6V plugs (fast heating) are fed the same 12volts, but since the coil inside is getting more voltage they heat up faster.

[moondoggie]

Good Day!

I don't know or care what voltage they're rated at. I can say with reasonable safety that NONE of them are rated for 12V, unless there was a GP I'm unaware of B4 the 9G. 9Gs & 11Gs, if fed B+ for more than 10 - 20 seconds will begin popping like flashbulbs - that doesn't support a 12V rating. :eek:

The only true 12V GPs I'm aware of were a long time ago. My friend's early 80's VW Rabbit must have had 12V GPs - when it got real cold out, it might be 90 seconds before the light went out & you could crank & start the engine.

The purpose of using sub-12V GPs is to speed up the wait. It works fine as long as you're careful. The built-in GP controllers don't allow them to receive B+ for too long, so you get quick GP heat & starts, & they hold up OK.

If memory serves, all resistance heaters (which GPs are) have a PTC (positive temperature coefficient). This means the resistance increases as they heat. The 60Gs, JK's, & probably some others have a higher PTC factor built into them, so (they claim) you can leave them on indefinitely.

If you don't know what GPs you have, simply hold your manual GP switch for 9 seconds or so. I did this for years in my 82, & never popped a GP. :)

Hope this helps.

Blessings!

[88 K30]

I think the CUCV plugs (13G's or 070 Wellman's) are actually 12V plugs (hence my original comment), but I won't swear to it...

[914turboford]

Thanks for the replies. I installed a manual operated solenoid switch today and got her started. Seems to run pretty good, actually. Then I dropped a 3/8-16 nut in the intake I think. I guess I'll pull the intake tomorrow. Attempts to fish it out with a magnet have been fruitless so far. The bigger problem as of now, however, is that it seems to need a new trans. It will not move in any gear. I can now see what went wrong with the previous engine. It seems to have ingested large quantities of water during a mud bog. What I can't figure out is how the PO managed to get it to the mud bog with a bad trans.

[ccatlett1984]

I think the CUCV plugs (13G's or 070 Wellman's) are actually 12V plugs (hence my original comment), but I won't swear to it...

The cucv GP's are 12v plugs (they see a short spike of 18volts when first activated) The Wellman 070's are the best plugs to put in a CUCV.

And the military humvee's use 24v plugs.

[moondoggie]

My wrong answer forgot 24V systems. Sorry. :( Good news is that 24V systems are probably < 1% of whats on the road.

[britannic]

I measured the voltage feeding the GPs on my CUCV and it was about 15V from the big ballast resistor on the firewall with a surface charge in the dual batteries.

[DmaxMaverick]

This whole 6V/12V thing is not relevant to the engine. The plugs are rated by the plug manufacturer for a voltage range. It just so happens the plugs heat quicker and hotter if they are "underrated" for the electrical system. A 12V plug in a 12V (as well as a 6V/6V) system will heat very slowly, and it won't get hot enough to do what it needs to do. Diesel engine and vehicle mfg's figured this out early on. In almost all instances, the GP rating will be 50% of the vehicle's actual electrical system voltage, be it US, European, Japanese, etc. The GP manufacturers rate the plugs for a different purpose than the application they are used for. If we were to install the "correct" voltage plugs in our engines, they would last forever, but would not be very effective.

The same principal applies to flashlights. If you want a brighter flashlight, just install a bulb rated at lower than your actual voltage. The cost is longevity, but they do brighten up.