GMC 2000 Sierra - Manual (Page 156)

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Engine Coolant Temperature Gage
This gage shows the engine
coolant temperature.
It also provides an indicator of how hard your vehicle is
working. During a majority of the operation, the gage
will read 210
_F (100_C) or less. If you are pulling a
load or going up hills, it is normal for the temperature to
fluctuate and approach the 250
_F (122_C) mark. If the
gage reaches the 260
_F (125_C) mark, it indicates that
the cooling system is working beyond its capacity.
The “Problems on the Road,” section of this manual
shows what to do. See “Engine Overheating” in
the Index.
Transmission Temperature Gage
(If Equipped)
If your vehicle has a heavy
duty automatic transmission,
you will have a transmission
temperature gage.
When your ignition is on, the gage shows the
temperature of the transmission fluid. The normal
operating range is from 100
_F (38_C) to about
265
_F (130_C).
At approximately 265
_F (130_C), the message center
will display a TRANS FLUID HOT message and the
transmission will enter a transmission protection mode.
When the transmission enters the protection mode, you
may notice a change in the transmission shifting
patterns. The transmission will return to normal shifting
patterns when the transmission fluid temperature falls
below 260
_F (127_C).