After putting the new thermostat in my 98 5.7 C-1500, I decided to pay attention to the way the gauges behave. I already knew that the gas gauge moved down fast ;-).

The temp gauge moves, it goes from about 150 to around 180 depending on outside temp and load on the truck. Takes quite a while to warm up in cool witner weather. The oil gauge varies from around 55 at cold start, to around 45 when hot at 30 mph. The volt gauge moves a bit, but it usually says 14 V.

Wondering why the truck runs so cool. Also why it takes a while to heat up.Same as the old thermostat, by the way.

Any others want to share what the gauges on their trucks say.

 

not sure about the 1988 model year but the next body style 99 would set a p0128 if the vehicle took to long to reach operating temp. If there is a p0128 diagnostic for your truck and this dtc is not setting...everything is normal.

 

if the heater blows hot like it should I wouldn't worry about it