2015 Denali cluster temp gauge inaccurate?

Denali62 · May 4, 2016

I installed a 170 thermostat and although the obd data shows 17x the temp gauge is way closer to the 210 mark.

My gut it telling me to go off of sensor data over a gauge but still that's a pretty substantial error.

TJay74 · May 4, 2016

I hope you also went in and turned of the MIL and error reporting for code P0128. once the cooler/cold weather returns the ECM will trip that code for running a thermostat that cold. If the ECM doesn't see 186° with in some many minutes of run time or so many key cycles the ECM will trip that code, kill all of the gauges other than the speedo, RPM and fuel gauge and not return them to use until the code is erased.

To answer your question, this isn't the first time GM has made the cluster gauge a dummy gauge. The 4th gen F-body's (Camaro/Firebird) were the same way. ECM would report accurate but cluster was off. The cluster would not report higher until the temp went up past the normal set point. I had thought GM was done with that logic though, I had a 160° stat in my 2006 GTO, 2008 TBSS, 2009 G8 GXP and 2008 Corvette and all of them reported the coolant temps accurately.

Jon A · May 4, 2016

I installed a 170 thermostat and although the obd data shows 17x the temp gauge is way closer to the 210 mark.

My gut it telling me to go off of sensor data over a gauge but still that's a pretty substantial error.

Yes, it's programed to read exactly 210° pretty much all the time so owners won't freak out and go to the dealer when the engine warms up a bit. It'll only show a tic below 210° even with the engine pretty darn cool. The one on my Denali reads exactly 210° from about 187 to 225 degrees. So once it creeps above 210° on the gauge you're pretty toasty....

Conversely I've found the tranny temp gauge in tow/haul is dead nuts on. That's nice.

I hope you also went in and turned of the MIL and error reporting for code P0128. once the cooler/cold weather returns the ECM will trip that code for running a thermostat that cold. If the ECM doesn't see 186° with in some many minutes of run time or so many key cycles the ECM will trip that code, kill all of the gauges other than the speedo, RPM and fuel gauge and not return them to use until the code is erased.

Are you sure you didn't flip a couple of digits? All the documentation I've seen shows 168° as the temp that needs to be exceeded--in which case a 170° thermostat will be fine. I have a 180° thermostat and it certainly runs below 186° much of the winter and I've never gotten a code.

Denali62 · May 5, 2016

Well at least it's a design flaw and not a malfunction hahagagag

At least I got my emblem pros emblem in and on today. Totally off subject

thetruck454 · May 5, 2016

Well at least it's a design flaw and not a malfunction hahagagag

At least I got my emblem pros emblem in and on today. Totally off subject

Is that the black stainless or the regular stainless, I can't tell

Denali62 · May 5, 2016

Black stainless I yanked the big gmc emblem and I'm gonna either strip the Denali emblem or have them make me a black stainless one

camcamaro1991 · May 5, 2016

What is the reason for the 170 stat? I hope you at least adjusted you fan turn on and off.

my 2 cents from tuning GM's for the last 10 years, GM's run better with stock temp thermostat put the stock stat back in asap! I don't think you understand what you actually changed, many tables pull from the ECT just 2 examples timing and fuel . Unless you update all the correct tables you not doing anything and this was a waste.

Denali62 · May 5, 2016

Well the main reason I changed it is because the ecm pulls timing over 192 I believe and I have witnessed my timing tables adjust to the cooler temp. My iat's are now within 5 degrees of ambient which it a lot closer than before and of course I changed the tune for the fans.

Not changing it unless I go cooler but I think it's right where I want it.

Jon A · May 5, 2016

What is the reason for the 170 stat?

Try datalogging while towing a heavy trailer up a long grade on a hot summer day. The stock thermostat and fan settings let the coolant, oil and transmission fluid temps to get way to hot for my liking. A few here have gotten warning lights from tranny fluid being over temp, etc, and had to slow down when towing in the summer with the stock setup. A cooler thermostat and more aggressive fan settings under most conditions won't allow the fluids to get anywhere near that hot.

tuning GM's for the last 10 years, GM's run better with stock temp thermostat

Also, 10 years ago GM's weren't coming with thermostats that begin opening at 207 degrees. Something in the mid 190's like prior vehicles would have been much more reasonable and negated much of the need for a change.

TJay74 · May 5, 2016

Sorry, yes I had the trip point swapped. It is 167° actually. With a 170° stat you can still trigger the P0128 code during cold months. I run cooler stats as well, while yes the ECM does use ECT for reference for fuel and timing it actually produces less power as the ECT temps climb, the timing is less aggressive the warmer the coolant gets. Even without programming the fans you will see a noticeable drop in coolant temps and the will stay more stabilized while towing and or driving hard during warm weather.

Stock stat is 196°, so no matter what you will never see less than 196° no matter how cold it is, reality is you will see 205°+ all the time. I know there is a 186° and the 160° stats out there. I have found that knock/KR/pinging is noticeably less with the cooler stats. GM only runs them at 196° as they need the engine to run hotter in order to insure a more complete combustion process to eliminate any excess combustion byproducts which allows the converters to do a better job of cleaning up the rest of the exhaust.

I have ran 160° stats on all of my GM LSx series engines, never had an issue at all. Always had great performance though and you could tell in the logs that the knock events were reduced versus the stock stat.

Jon A · May 5, 2016

Stock stat is 196°, so no matter what you will never see less than 196° no matter how cold it is,

But it's not. It's 207°. The number is stamped right on it. Why do people keep saying that?

When scanning, even in the winter time you will never see below 207° for any length of time after initial warmup--unless you're coasting down a mountain pass (in which case your injectors are shut off and the engine is "air cooling" beyond the thermostat's control).

Denali62 · May 5, 2016

My truck is fast

And runs cooler

That's all I know

camcamaro1991 · May 6, 2016

Try datalogging while towing a heavy trailer up a long grade on a hot summer day. The stock thermostat and fan settings let the coolant, oil and transmission fluid temps to get way to hot for my liking. A few here have gotten warning lights from tranny fluid being over temp, etc, and had to slow down when towing in the summer with the stock setup. A cooler thermostat and more aggressive fan settings under most conditions won't allow the fluids to get anywhere near that hot.

Also, 10 years ago GM's weren't coming with thermostats that begin opening at 207 degrees. Something in the mid 190's like prior vehicles would have been much more reasonable and negated much of the need for a change.

I do data log with 7500LBS in TX (pretty sure it's hot enough) never had a issue. I do believe the rad cools all 3, oil, coolant & trans now, so I can see why it would be warmer than previous gen's

Yes I 'm aware they were cooler on the older vehicles.

TJay74 · May 6, 2016

But it's not. It's 207°. The number is stamped right on it. Why do people keep saying that?

When scanning, even in the winter time you will never see below 207° for any length of time after initial warmup--unless you're coasting down a mountain pass (in which case your injectors are shut off and the engine is "air cooling" beyond the thermostat's control).

Sorry then, last one I pulled was for my 2009 G8 GXP which still was using the 196° stat from the factory. With the EPA still pushing for higher MPG numbers I am sure the manufactures are doing everything they can to fully burn 100% of the fuel as possible and not have as much emissions to deal with as well.

Jon A · May 6, 2016

I do data log with 7500LBS in TX (pretty sure it's hot enough) never had a issue.

Yeah, TX is flat enough I doubt you'll have any issues. The heat mostly becomes an issue up long grades where you're at or close to WOT for 5-10 minutes or so straight.

I do believe the rad cools all 3, oil, coolant & trans now, so I can see why it would be warmer than previous gen's

Yes, it has an engine oil cooler and transmission oil cooler inside it, so the cooler you keep the radiator the cooler those fluids will be as well. Also the tranny has an air/oil cooler which does a lot more when the fans are cranked up--and you can crank them on sooner with the cooler thermostat (with my current settings my fans would be blasting full blast all the time with the stock thermostat).