GMC SIERRA 1994 Manual page 76

NOTICE:
After you've used the coolant heater, be sure to store the cord in
the manner it was, to help keep it away from moving engine
parts. If you don't, it could be torn and damaged.
How long should you keep the coolant heater plugged in? The answer
depends on the weather, the kind of oil you have, and some other things.
Follow this chart.
Engine Coolant Heater Usage
Viscosity/
32°F to 0°F
Oil Grade
(OOC to -1SOC)
SAE
1 OW-30
SAE
I5W-40
Not
Required
Not
Required
0°F to -10°F
(-18" C to -23
O
C)
Two
Hours*
Two
Hours*
Below -10°F
Below -23
"
C
Eight Hours*
or Overnight
Eight Hours":
or Overnight
*The times listed are minimum times. It will not harm either the coolant
heater or the vehicle to leave the coolant heater plugged in longer than the
times stated.
For best results in cold weather, use Number I-D diesel fuel or a
"winterized" Number 2-D fuel.
lf Your Diesel Engine Won't
Start
If you've run out of fuel, look at "Running Out of Fuel" (see "Diesel Fuel
Requirements and Fuel System" in the Index).
If you're not out of fuel, and your engine won't start, do
this:
Turn your ignition key to RUN. Make sure that the "GLOW PLUGS" light
is out. Then turn the ignition key to START.
If the light doesn't go off, wait a few seconds, then try starting your engine
again. And, see your dealer as soon as you can for a starting system check.
2- 18