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Some of you like myself, may already know that factory gauges may not always be super accurate. I’ve been a GM tech for 24 years and I can tell you that it seems the newer trucks (say K2 and T1’s) are much more accurate than say anything from the 90’s and early 2000’s. For proof, I have a few pictures of my 2006 from this morning.

Now, keep in mind that dmax thermostats are both open right around 185 degrees. While I have previously cleaned out my dirty cooling stack and I have replaced both of my t-stats just because of age/mileage, my temp gauge can move like the tach and oil pressure gauge will sometimes. Honestly, a lot of vehicles that I’ve owned or worked on in this era seems to have similar issues and I’ve found the same issue every time. For some reason, the ipc is just not capable of accurately depicting what the ecm is telling it.

So, during this test I initially started the truck cold and while it was idling/warming up, I saw the gauge start to move off the bottom/160 mark when the ect (engine coolant temp) sensor was only reading 113 degrees. By the time the coolant got to 160 degrees, the gauge was reading 185 (middle mark between 160 and 210). From 160 until what you see here, this is as far as the gauge moved.
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And here is the live data from the scan tool...
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So I cranked the engine speed up and found the gauge to get to the point that I normally see it at, while driving at speed on the road, even when towing the wife’s 7500lb camper.

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And once again, the scan tool data to match this gauge reading. Well, match, may be a strong word for this...

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Unfortunately, there isn’t a fix for this but it’s good to know that my suspicions were correct. While I know full well that I can install some sort of aftermarket gauge I am really just not a fan of them. Maybe someday, after I maybe tune it, I will put an Edge CTS reader in it but honestly, I’d rather not deal with that hassle either.

I do have a few ipc backlight bulbs out so while I’m in the ipc to replace those, maybe I’ll replace the stepper motors and see what happens then. I’m doubtful that anything will change but I guess I won’t know until I do it.
 

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For the LLYs, most of them exhibit this behavior...
  • starts coming off the 160*F on the gauge when OBDII will show it coming off 113*F (same as yours above).
  • both ramp up linearly, meeting at about 180*F. So when the gauge says 180*F, it really is 180*F (or very close).
  • gauge ramps up to about 200*F (left of center) as actual gets to about 188*F.
  • gauge stays remarkably steady at 200*F while actual can go up to about 218*F (yes, 188-218!!).
  • gauge then runs about 10-15*F below actual above that.
TxChristopher (TxC, TxChris) did the original mapping back in 2006. My LLY follows this pattern.
 

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Some of you like myself, may already know that factory gauges may not always be super accurate.
You, my friend, have proven yourself to be a Master of Understatement! (y)
 
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