GM-GMC: 6.2 diesel, ac delco, glow plugs

Question
        I have a 1982 6.2 diesel in my gmc truck, about one year ago I bypassed my faulty glow plug timer with a momentary switch in the dash. I ran it through the original solinoid on the fender well to keep all or the current out of the cab. It seems to work good although it is time to replace my glow plugs and I have heared from some people that the plugs should only be getting 6 volts and I dont believe them. So I bought the new plugs and am afraid of installing them until I figure out the correct voltage 6 or 12. So if you would help me out I would like it.  

Answer
Jason,

Like everything else on a 6.2 diesel, it comes down to amperage and not voltage.  That is why there are two start batteries on 6.2 diesels.  The voltage on the batteries drops to 10 or 11 as soon as the glow plugs are turned on.  It drops even further when the starter is engaged.

My point is that the voltage rating of the glow plugs is not important.  With a manual glow plug control system (both of my 6.2 diesels are manually controlled), the most important issue is obtaining positive coefficient temperature (PTC) glow plugs.  These are also known as self-limiting and they turn themselves off and on to prevent overheating, swelling, and burn-out.

I use AC-Delco 60G glow plugs, and they are rated at 10.5 Volts.  Some people do not like them because they heat a little slower than other glow plugs and may not work well when used with the OEM automatic glow plug controllers.  There are other brands out there that are PTC as well.

If you have the original glow plugs in your engine, they may be AC-Delco 9G and these were known to swell their tips, especially if manually controlled.  You may find it difficult or impossible to remove one or more of them.  Do NOT force them and cause any tip(s) to break off.  If you do, you may have to remove the cylinder head to get the tip(s) out of the cylinder(s).  Spray penetrating oil into the glow plug hole and work the glow plug side to side and in and out to help break up carbon and get it (them) out.