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My GS runs great when it is 115 F or above in traffic with the AC on full it stays at 210 or below. So what if it cycles a little above and below 180 when it is 50 F and get a yellow bar occasionally. It doesn’t require excessive warm up time indicating a stuck open thermostat and doesn’t overheat indicating a stuck closed thermostat. There is no problem.
^^^
Perhaps but the air/fuel MAP uses temp as a key input on where to set it. At some lower temp it is setting a richer mixture. I have been on the C7 forum even before I got my Z51 the 1st week in October 2013. I don't recall any posts discussing the yellow halo coming back after warm up. Perhaps there were some but it appears to me GM got some incorrect thermostats!
I also run about 190/195 min NOT 180. The Z51 was the same as my Grand Sport. As I showed in post #16 the Service Manual says the thermostat should start to open at 188 F and be fully open at 206 F.
In central fl this morning it was 46 now thats cold for us. I warm up my car then the wife and I take off for breakfast. As I'm driving,( well first the car went to operating temp) the temp went down to where the yellow came on around the RPMs gauge.
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What was the actual engine temperature it was going down to though? I don't know if it's the same for all years of the C7, but on my 2018 the yellow bars (at 3500ish rpm) disappear when the coolant temp hits 163F, and once my car goes past that threshold it never goes down below it again (until I shut it down of course), it'll keep going beyond 180F and that's about the coldest it will stay at, even if it's 25F outside. So mine never gets even close to the point whre those yellow bars will reappear.