After three years of GMT360 ownership, I have researched the daylights out of the cooling system on this platform. A couple of factors to take into account.
For starters, the temperature gauge is not an accurate measure of engine coolant temperature. A 50/50 mix of Dex-Cool to distilled water will give you a boiling point of 265 °F – the engineers have factored this into account when they designed the cooling system. As long as the coolant temperature remains between 188 °F - ~245 °F, the gauge will read 210 °F/100 °C. When it starts approaching 250 °F, the needle will shift to between 210 °F – 260 °F (or in my case, 100 °C– 125 °C). To determine your exact coolant temperature, you will need a scan tool – personally I have a ScanGauge-II hooked up all the time and care less about what the idiot gauge reads.
Whatever the reason may be, this platform doesn’t like ambient temperatures over 100 °F. If you’re sat idling in traffic, or slow moving traffic where there’s little air flow, expect coolant temperatures in excess of 210 °F. With an ambient temperature of 118 °F, I’ve had mine range anywhere between 206 °F – 230 °F with the air conditioning on. If you push the engine over 60 MPH, 211°F – 215 °F at highway speeds is a common occurrence at such temperatures. Turn the air conditioning off, and coolant temperature will drop down to 195 °F – 198 °F at highway speeds.
That being said, a lot of engineering went into the fan clutch design. It’s capable of moving 10,000 CFM of air. It was designed for heavy towing, which is why this platform never received an all-electric fan. That being said, they still put in a single row radiator, which I think was a pretty stupid move. Turning on the air conditioning bumps up the fan speed by 10% - you’ll get cold air blowing from your air conditioning, but if you’re almost stationary, it doesn’t really do much for engine coolant temperature. The fan will not engage at 100% unless – engine coolant temperature reaches 264 °F, transmission fluid temperature reaches 304 °F or AC pressure exceeds 240 PSI. The PCM controls fan speed based on coolant temperature, ATF temperature, AC pressure, vehicle speed, ambient temperature and intake air temperature.
You have a ’02 – the fan clutch was upgraded in ’04 and a PCM patch was made available in early ’05 for the new clutch. Before you do anything at all, I would highly recommend you replace the fan clutch if you haven’t done so already. The OE clutch is made by Behr – you can pick up a GM Original Equipment P/N 1540133 or a Behr P/N 376734021 as a replacement. This is one of the parts this truck is picky about – some aftermarket fan clutches are known to spin slower, etc. triggering the check engine light.
