Interesting Fan/Denali Temp Gauge Observations

Jon A · May 15, 2014

I did some experimenting.... I removed the fuses for the engine fans to make the thing warm up a bit.

First observation, the temp Gauge. It should be no surprise GM makes a "dead spot" in the temp gauge at normal operating temp so drivers don't fret if it gets a bit warm, etc as they've been doing that for a long time. With the digital gauge of the Denali, they can obviously control this very precisely. If you've noticed it never moves off the 210 degree mark, no you're not imagining things and no, the engine really isn't running that steady a temp.

I didn't pay quite as close attention on the way up, but somewhere around 190 degrees (ECT on a scanner) the temp gauge jumps to 210 and stays there. It won't move off the 210 mark until the actual temp is about 225 degrees. So, with the Denali you have a "dead spot" of about 35 degrees where the dash gauge won't move off the 210 mark. Not even a millimeter. While I would certainly prefer an accurate gauge, I don't think there's anything we can do about it. If you want to know the actual temp, use a scanner (Torque on your phone works fine for that). The reason I did this was simply to find out exactly how hot it had to get to make that virtual needle move--answer is 225. Non-Denalis won't be exactly the same, of course, but I'd expect they have a pretty large "dead spot" built in as well; somebody else will have to figure out the translation for those gauges.

The second thing I learned during this test I really didn't know about--once you exceed a certain temp (225 or 228, I'm not sure which is the controlling table), your fans will stay on at 51% speed after you shut off the engine. Over 234 and they'll stay on at 76% speed. For up to 5 minutes.

I had seen the settings in HP Tuners, but this computer has all sorts of settings (supercharger, turbo related, electric water pump, electric thermostat, etc) that aren't used so I didn't know they were "activated" or whatever. Apparently, they are.

This is good news in my opinion. When I put an aftermarket electric fan in a vehicle I usually wire an override switch that can turn on the fans with the engine off for exactly this reason. This is great if you do find yourself overheating--you can pull over and shut the engine off and the fans will cool the water in the radiator without your engine producing heat. Shut the engine down and let the fans run for a while, start it up and it's instantly cooled off.

You can put the settings wherever you want as well with HP Tuners or the like. Another useful purpose is for those who drag race--they can set the temps really low so the fans will always stay on for a while after a run, helping it cool down much faster.

Anyway, I figured this was pretty useful info as Summer approaches.

TJay74 · May 15, 2014

A over-ride switch will not work on these vehicles unless you use a pulse width modulated (PWM) controller. It is not a simple on/off toggle anymore to get the fans on due to the fans running variable speeds now. If you cool the engine under 167° it will also trip a SES light, the ECM thinks the thermostat is stuck open. You would have to turn off reporting on code P0128 to get that to stop, otherwise it will kill some of the gauges until the code is cleared.

I usually go into the calibration thru HPT and change the fan profile myself, I hate waiting until the engine gets over 210° to cool down, but then again I usually also change out the thermostat to a 180° as well.

Jon A · May 15, 2014

Yeah, with PWM you need a controller to do the override when you hit the switch, you can't just do it directly. I used a Painless 30140 PWM controller on my Trailblazer and it came set up for that. I'm not sure how you'd rig one on one of these vehicles. But as I was saying, with the engine off mode I don't think a switch is really needed--set the engine off temp pretty low and the fans should come on when you turn off the engine to cool the radiator right away.

I hope somebody comes out with a 180° thermostat soon.