I have a melted relay on my truck, so the grids are dead. It lit right off at 4 degrees this morning, no grids, just the block heater. Coldest unheated start so far was 15, lit right off, idled lumpy for 10 seconds while laying down white smoke, then cleared right up. I ain't fixin' it, works fine for me without them.

 

The glowplugs in my TDI are located next to the injectors. I've never had to glow more than 10-15 seconds and that was down to -8F in Iowa. If it's above 32 degrees, glowing isn't necessary, it'll fire right up.

VW also incorporated 3 glow plugs into the water outlet to the heater core to aid interior heat. In my A3, you activate them by putting the fan switch on "3" and heat to maximum, air intake to recirc. I've tested it myself, the interior will warm up far quicker that way than turning the fan to "4".

In the newer A4 TDI's (99 and above), they're controlled automatically depending on temperature.

 

I didn't like the glow plug set up in my 89 ferd 6.9 I had that truck for seven years & seemed like I was always replceing glow plugs.
I love my ctd