2017 Silverado 5.3 - Temp Gauge Fluctuation

Mr. Pibb · October 1, 2023

Need Help Please!!!! I truly appreciate anyone that reads this long post. Hopefully someone can help me figure this out.

Bought my 2017 Silverado CrewCab LT Z71 new. For 5 yr & 10 mo. the temp gauge sat at 210 with no issues and no variation. Then, in June 2023 the temp started rising about 10 degrees and would fluctuate from there back to normal.

Thermostat was replaced, didn’t resolve the issue.
Temp sensor was replaced, didn’t resolve the issue.

Truck is well maintained, radiator/coolant flushes done a normal intervals with no issues found.

Dealership has checked out this issue 3 times and says it’s operating as normal, temp fluctuation is normal.

I have been calling BS on this since June, how is this normal? Almost 6 years with no variance but now it’s normal?

So here I am in October, with continued temp issues that are anything but “normal” The temp gauge has progressively increased, the gauge goes up to 245-250 then will drop back down to 210 and fluctuates between 210 - 230/235 as the drive continues.

Things to note:

I have never had a Check Engine light, adding to the frustration.
Coolant level doesn’t change, no leaks whatsoever.
This temp issue does not happen when idling. I’ve idled for 20-30 min both from cold and after driving with the issue happening, no fluctuation.

I have thought through some other possible issues but then wonder could it be “this” when the issue is not consistent or throwing codes.

Are the active shutters not opening / operating correctly, that should throw the check engine light
Belt is loose, again should be a more consistent issue with sounds and other functions having issues.
Water pump going out, again I think that would cause more consistent issues and would overheat the engine.
Fan(s) going out, wouldn’t that be more of an issue when idling vs driving and would be a more consistent issue.
Could this be some other sensor, relay, electrical issue.

Any help, experience, and/or suggestions you have on this issue are greatly appreciated.

rav3 · October 1, 2023

How many miles on it. Have any modes been done?

Mr. Pibb · October 1, 2023

No Mods, 97k miles

mikeyk101 · October 1, 2023

Did you replace it with an aftermarket thermostat or an OEM one?

Mr. Pibb · October 2, 2023

OEM, for the Thermostat and Temp Sensor

mikeyk101 · October 2, 2023

I agree that something is going on. If you were hauling a trailer in some more challenging areas, the higher temps would make sense. But if you are just driving around in average areas, I agree that it's not normal. In my case, last winter, my OEM thermostat went bad and my dash gauge wouldn't get up to the 210⁰ like it had done for years even on the coldest days. I decided I wanted to change from the OEM 207⁰ to an aftermarket Motorad 194⁰ thermostat. I switched to a cooler one because I sometimes tow a toyhauler and had experienced some higher than normal temps especially in areas with steep grades and figured if the thermostat opened a little sooner, the radiator would help with keeping coolant cooler. It worked well for a couple months and the dash gauge showed the steady 210⁰ all the time. Then several months after installing, I experienced the motor running hotter than normal especially when running at higher speeds or accelerating a little faster than regular. I switched it out for an OEM 194⁰ that is found in several Corvettes and Cadillac CTS models and haven't had a problem since. Dash gauge normally stays at the 210⁰ except for occasional temp increases when towing toyhauler in more challenging terrain.

One thing I would mention is that the dash gauge is very generic. When it shows 210⁰, the coolant can actually be anywhere from 185⁰ to about 225⁰. So if it moves higher, it is already well past the 210⁰ temp. The best way to monitor the current coolant temps is through an OBDII reader. I use a BAFX Bluetooth reader and Torque Pro app on my phone.

But yours is odd. I'm wondering if maybe the replacement thermostat is defective? Any chance you are having an issue with your cooling fans running all the time?

Mr. Pibb · October 2, 2023

I had experienced the fans running even after the engine was off before the temp sensor change. They still seem to be running more than usual but haven’t been running after the engine is off.

2018z71midnight · July 4

Hi there, did you ever resolve your issue with the fluctuating temp I am having the exact same issue you are. I had the dealer do a full coolant flush and fill and also have them change the thermostat and housing to OEM and the fluctuation hasn’t changed. I’m afraid that when I do end up towing it will exceed past the recommended operating temperature, any advice would be much appreciated. Thanks.

Edgar Salvatierra · July 4

I'm havi.g the exact same issues and can't find the problem did a thermostat change from the oem to 160. Also new tempsonsor and also a new radiatir fan assembly and still won't resolve the issue. Dealer told me they can't reproduce the problem.

Homewrecker007 · July 5

6 hours ago, Edgar Salvatierra said:

I'm havi.g the exact same issues and can't find the problem did a thermostat change from the oem to 160. Also new tempsonsor and also a new radiatir fan assembly and still won't resolve the issue. Dealer told me they can't reproduce the problem.

There's a good chance the head gasket is bad. Are you loosing coolant at all? The direct injected engine is harder to diagnosis a bad head gasket if it's a tiny bad spot. Coolant won't show up on spark plugs and most likely won't get in the oil pan.

Yotaman · July 5

My 2014 temp started fluctuating down from 215 and back up while running a few years ago. I did search and found out the thermostat was defective. I think GM updated maybe to a new part number. I replaced mine and no issue since. Search for radiator cracking it was caused by the cycling T'stats.

Yotaman · July 5

My 2014 temp started fluctuating down from 215 and back up while running a few years ago. I did search and found out the thermostat was defective. I think GM updated maybe to a new part number. I replaced mine and no issue since. Search for radiator cracking it was caused by the cycling T'stats.

Found this from when I swapped mine may help

Mr. Pibb · July 6

I have not been able to resolve the issue. I continue to be told that it’s “normal”.

This issue continues to puzzle and frustrate me. I’ve read the comments about head gaskets, radiator leaks, etc and that’s solid information but I have a wrench to throw in that.

1st, I have no coolant loss and 2nd,

Wouldn’t those issues persist at any and all times when the engine is running (Hwy, City, or Idle) which is not the case here. This is happening during acceleration, from a stop light/sign, getting on the hwy, or passing.

I’m obviously not an expert and I apologize if I sound like an idiot here. I still think this could be the fan or shutters. Fan doesn’t show any issues on a diagnostic. However, maybe someone can answer this; If the fans are functioning but either the high / low speed isn’t, (I believe the fans have multiple speeds) would that show on a diagnostic. Basically could it not be operating correctly but enough to fool the diagnostic.

2nd idiot question, I know the dealer has told me if there is any issue with the shudders, it will immediately throw a check engine. Well is it possible they are not opening as quickly as they should, allowing the engine temp to climb higher than expected.

The aftermarket thermostat is an interesting thought. I guess the question here is are there any negatives to running a 160 vs. OEM. I know several have noted that this didn’t fix the problem but maybe it would at least help counter the higher temps until the issue is identified.

I truly appreciate all the time and info provided by everyone. I hope that a clear resolution can be found & documented at some point to help everyone impacted.

Homewrecker007 · July 6

6 hours ago, Mr. Pibb said:

I have not been able to resolve the issue. I continue to be told that it’s “normal”.

This issue continues to puzzle and frustrate me. I’ve read the comments about head gaskets, radiator leaks, etc and that’s solid information but I have a wrench to throw in that.

1st, I have no coolant loss and 2nd,

Wouldn’t those issues persist at any and all times when the engine is running (Hwy, City, or Idle) which is not the case here. This is happening during acceleration, from a stop light/sign, getting on the hwy, or passing.

I’m obviously not an expert and I apologize if I sound like an idiot here. I still think this could be the fan or shutters. Fan doesn’t show any issues on a diagnostic. However, maybe someone can answer this; If the fans are functioning but either the high / low speed isn’t, (I believe the fans have multiple speeds) would that show on a diagnostic. Basically could it not be operating correctly but enough to fool the diagnostic.

2nd idiot question, I know the dealer has told me if there is any issue with the shudders, it will immediately throw a check engine. Well is it possible they are not opening as quickly as they should, allowing the engine temp to climb higher than expected.

The aftermarket thermostat is an interesting thought. I guess the question here is are there any negatives to running a 160 vs. OEM. I know several have noted that this didn’t fix the problem but maybe it would at least help counter the higher temps until the issue is identified.

I truly appreciate all the time and info provided by everyone. I hope that a clear resolution can be found & documented at some point to help everyone impacted.

As I stated in my post bad head gasket is harder to diagnosis on the direct injection engine. No it doesn't present itself all the time, it's mostly present under a load. My truck is a 2014 I don't have shutters, it has the same problem the dealer said it was a head gasket. A mechanic friend of mine said it is the head gasket. As far as the thermostat goes I don't like these thermostats and will eventually swap it and the housing for one I'll include a link for it. The 160° will work fine if you are south of the Mason Dixon or in California. Northern winters with a 160° thermostat you won't have any heat coming out the vents. Also the truck needs to be tuned for the 160° so the fans work properly and it doesn't throw codes for not getting to temp fast enough.

https://www.montmotorsports.com/dms-billet-thermostat-housing-w-ls3-style-160-degree-thermostat-gen-v-lt/

Edited July 6 by Homewrecker007