I had a few questions considering the normals for coolant temperatures with regard to ambient temperatures.

I have been noticing that when idling for long periods of time that my coolant temperatures will climb to above 210F, with the highest I've seen so far is half way between 210F-260F (~235F). The truck had been idling for about 30 minutes, and ambient temperatures were about 95F (no wind). At the time I noticed that, I throttled the engine up to about 1400 RPM, and within about 5 minutes it was back down to normal. When driving down the highway, it holds steady just under 210F.

Either way, have other people experienced the same thing? I'm assuming its because of the stagnant air, and no heat transfer across the radiator as there is no head wind into the grille. I would expect that the belt fan should be doing that to supplement, but maybe not?

Would anyone recommend a coolant system flush and service? Or replace the thermostat? (Would anyone recommend a lower temperature thermostat for living in a hot summer area?) Water Pump not putting out full flow?

Any advice would be greatly appreciated!

Thanks!

Back in the day, I had a neighbor that had a 2000 Bravada that was left unattended for a similar period of time with the A/C running, and when we got back to it, its temperature was at that same spot as well, and the temperature came right back down on it when the engine speed was picked up.

At the time, I figured that the engine driven waterpump combined with the engine driven fan were all turning slowly and were doing the best that they could given what they had to work with.

I wouldn't go out of my way to change thermostats or coolant flush specifically for this issue, but if it'* coming up time for it anyway, it may not be a bad idea to do it sooner rather than later. I would also suggest clearing the radiator and condenser of any debris, and then cleaning with simple green or similar to restore any possible lost airflow.

I don't know the exact temperature the truck is running, as GM has been known to pin the gauge at 210* with any reading between 190* and 215* (not sure on the exact range). Changing to a lower temperature thermostat would likely be of no benefit, as naturally aspirated motors don't typically run differently at 180* vs 190-210*, and it may not even change anything, as the fan is what controls how hot the engine runs when stopped. The fan also has a clutch that will allow slippage until 210-215*, at which point it should lock (you'll hear it if it'* locked and you push the engine speed up).

When running the open road, it typically should be riding against the thermostat temperature unless pulling a hill or otherwise working hard. If you are concerned about this, verify the exact temperature with a scanner before assuming the gauge is correct, because GM is not known for precision accuracy in their gauges.

Considering the ambient temps, and not moving/sitting parked idling, I'd say the temps sound normal.

Agree with rjolly87 and WilliamE.

I'm also guessing you are running the air conditioning while idling?

I'll also submit that a lower temperature thermostat would not help this situation. In this situation the thermostat is full open. Whether it started at 180 or 195 it is still handling the same situation: idle engine speed, slow coolant movement, slow fan movement.

I'm of the mindset that an engine can't have too big of a radiator . . . except maybe in Alaska in winter. If you want your Sierra to run cooler in this situation and all the other situations, I have a couple of suggestions:

1. Swap out the radiator for one with more rows. As many as you can fit. More rows gets you more heat transfer to the same amount or air flowing through.

2. See if there is a severe duty fan clutch available. It will move more air at idle and all other engine speeds. Many non-severe-duty fan clutches "freewheel" at engine speeds above 1800-2200. The idea here is that these higher engine speeds are temporary therefore it can afford a slight heat rise then make up for some of it with airflow from movement of the vehicle and the rest of it when you back off the throttle as you approach your desired speed. This saves some noise and wear and tear on the water-pump bearings. Yours being a K2500 may not do this and may have a heavy-duty or severe-duty fan clutch, but not a "severerer-duty" unit like some that are available. I always choose the severest-duty fan clutch available for a vehicle. Do your idling then start driving and you'll hear the difference and see how much more quickly it recovers.

Same goes for rjolly'* neighbor'* Bravada, although much bigger pain to do.

I like the idea about the different fan clutches!

Thank all of you so much for your input, and I apologize for the delay, in replying.

I would like one more opinion, if possible. What do y'all think about a high idle switch? Is it possible to do with this engine/electrical configuration? If so, how difficult is it?

Thanks!

Do you idle your truck for 30 minutes on a regular basis?

Not quite 30 minutes. It'll start to creep at a drive through. Every now and then I'll idle the truck to keep the AC running while my daughter is in her car seat napping.

Rule 1) Never wake a sleeping baby. Haha

Either way, I notice it creep to between 210-235 at short intervals (between 5-15 minutes at idle)

I'm sure there may be a larger problem, such as insufficient fan blade speed at idle due to a worn fan clutch. But it could also be as simple as sitting in SC heat. (Heat index is regularly >100F this season), with a 13 year old truck doesn't work too well.

If you think something is a bit off, I would start at the front of the truck. Carefully cleaning and straightening the fins (if bent) on both the condenser and radiator can go a long way to restoring lost performance of the cooling system. Also make sure that you are not missing any shrouds and air deflectors that may have not made it back on the truck in the course of its life.

Simple green is good for cutting general grime. Water hose and compressed air can be good at blasting dirt away. Soft brush and smart cleaning methods are a must, or else you can make it worse.

If the cooling system has seen better days, a good coolant/radiator flush can go a long way too. Essentially, if maintenance hasn't been done, there is nothing to lose by doing it.

195 degree thermostat is already at the 210 threshold or higher with stop and go traffic. The ac is adding more strain and heat in the engine and cooling system. Your engine temps seem normal with your high ambient temperatures. I have a 1997 Chevy Silverado 5.7 that I tossed the clutch fan and installed a Proform e-fan with a 180 degree stat. Wired into the ac clutch the fan only runs when the adjustable coolant temp reaches 195-fan brings it down very quickly-or with the ac compressor on. With the ambient at 95 ac reaches 35 degrees on max cool in stop and go traffic. A junkyard e-fan with a thermostat kit is a cheaper option.