Intermintent Cooling Fan problem

[SB42]

I have electric fans on a 06’ Sierra 6.0. Twice in the last 2 months (or so) I’ve had them not turn-on when they should have been on. I happened to notice because I could smell it running a little hot and my temp gauge was all the way to 210-ish. I switched on the heat to help dissipate the extra heat. When I started the truck up a few minutes later the fans turned on and all was well. (not that it should matter but I was at 8-9K ft. both times. I know this impacts the coolants’ properties but I wouldn’t think it would have any impact on the fans themselves)

 

The only work that’s been done on the truck lately was some fluid flushes including the coolant. Seems unlikely that this would be related but thought I would mention it. Prior to me realizing it was the fans, I tested the coolant to ensure that the dealer put the right mixture in and it tested fine. The first time this happened I thought maybe they disconnected the fans during the flush process but verified that the connectors looked fine and since the fans have been running since, I ruled that out.

 

What do I need to check next? Seems odd to me that its intermittent. Seems like it’s a sensor type issue of some sort but that doesn’t quite click for me since the gauge is reading fine. Could the thermostat be acting up? I couldn’t quite wrap my head around how that would influence the fans….

 

Let me know what y’all think I need to check next. Much appreciated!

 

Sam

[Duelin]

Most GM vehicles have their fan kick in around 228° and kick off around 214°. GM likes the engines running at this temp for a couple of different reasons. The 14° range between 228° and 214° means less expansion and contraction which means less movement between the heads and block. Which means less problems with head gaskets. Also at that heat range it keeps any moisture that is in the engine in vapor state and the engine is able to pull it out thru the PCV system. No moisture means no sludge. Also at that temp range there is less emissions. LIke txab said if you have a scanner you could look and see what temp the computer is kicking the fans on and off. And if you had an infrared thermometer you could compare the two. There is a possibility that you could have a bad CTS sensor.