About two months ago I went on an hour plus drive in my 14 7M Z51. Had no problems getting to my destination. On the return trip I noticed that the AC and rev match didn't work, and the temp gauge on the dash was at zero. When I got home, the fan stayed on full blast. A restart showed zero degrees on the digital performance screen and the fan still stayed on. I changed the sensor, which when tested with an ohmmeter showed the same value as the new one, which didn't fix the issue and so I disconnected the battery as suggested, which did fix the problem and returned everything to normal. I chalked it up to a bad sensor. Two months later the same thing happened again on the next hour plus drive with the temp needle at zero and the fan at full blast after shutdown. Drove back home, disconnected the battery, reconnected, and all again is fine. I've seen quite a few people on fb corvette forums report this same issue and it seems a battery disconnect/reconnect solves it. I've heard camaros have the same issue.

I know its possible that this may be a sign of a failing battery. I bought it in 18 and it may be the original battery which would make it 8 years old. However, this problem has occurred on only long drives. Most of my daily driving is 20 minutes or less, and I notice that the water doesn't really ever get to 185 or so. Most of the time I have the AC on which keeps the fans on and the temps low. Shutting off AC does allow the temps to get hotter. My c6, when it had a failing thermostat that stuck open, would set a code if it didn't get to operating temperature in a certain amount of time. I don't get any codes on the C7, unlike the C6. Is it possible that the same thing is happening here but manifesting itself differently? Does the ECU have any monitors watching temperature over time and doing funky things if it doesn't see what it expects after a certain amount of run time? Do I change the T stat next, or throw a new battery at it? It starts up fine every time but I have managed to kill the battery twice with the fans staying on too long and draining the battery. Voltage is always in the 14.5V range or higher.

Thanks in advance for any information anyone can provide. Sorry this is so long winded

 

I would definitely first try a new battery, or at least cleaning and double checking the battery terminals. The battery may be fine until it warms up.

If that doesn't work, you may want to grab a VXDIAG VCX Nano or similar so that you can query each module on the GMLAN/CAN and see if they return any error history that might be helpful.

 

My 16 is doing this also. It happened on a road trip 2 weeks ago. . I unhooked my battery and it has been fine since. Going on another road trip next week. Let see if it returns.

 

Update: I managed to get the situation to occur again on a long drive at fairly low air temps. It happened no more than ten minutes into the drive and oil and water temps were in the low 150s. So Ive replaced the thermostat with a stock temp of 207 which seems really high to me. Anyway after refilling, going on a short drive, and topping it up we will see how it works. I may want to drop in a lower temp t-stat but we will see if I can get the failure to repeat. Is there a favorite temp and or vendor to get a lower opening thermostat?

 

My next road trip is Monday. Interested to see if this is going to happen again. I may go in touring mode. I read somewhere it's not as likely to happen in touring mode. I keep a 10 mm wrench in the car to un hook battery if necessary.

 

I can't say what mode its more likely to happen in. Don't know why it would make a difference but I only use touring mode, and all of these occurrences happened in touring. I too kept a 10mm socket in the car for a battery reset but have been optimistic and put it back in the toolbox after replacing the thermostat today, which also uses 10mm bolts!

What were your water and oil temps when it happened, and what was the outside air temp?

 

We went to Laughlin Nevada on a Friday which is about a 200 mile run. It ran fine Friday and Saturday. When I fired it up to return on Sunday it started immediately with no heat gauge and the fans blasting. It was in the mid seventy degrees out side. My oil temps seemed normal. I unhooked the battery when I got home. Took it to the dealer on Tuesday and they said everything was fine. It never threw a code. .

 

I am brand new to the forum with a "new to me" 2016 C7 Z51 I've only had for one week. Took the car out last night for a 50 mile round trip drive (25 miles each way) and on the return trip it did exactly what yours are doing. No rev match, no temperature reading and fans kept running after shut off. I'd never experienced it in another car so I disconnected the battery and went to bed. Naturally I'm thinking it's a voltage issue - like a bad battery as I know low battery voltage can cars to do strange things. Put the battery on the charger before I went to bed thinking it might help.

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It might be a tired battery. Seems lots of folks with C7s fix a lot of problems by throwing a new battery at it. I've always suspected a flaky t-stat in my car so I'm shooting for that first. Really slow to heat up and in low temps it doesn't get much over 160, usually 150. I don't think I've got a weak battery but it has been abused a bit so its possible mine is giving up the ghost as well

 

Thanks - I'm going to go with a t-stat and temp sensor replacement. Looks very straight forward and at least I'll be able to rule those out.

 

Common tstat failure. Causes those exact symptoms if car does not get near operating temp in X minutes. A car not heating up makes the issue very obviously the tstat is stuck open.

 

My car reaches operating temps when it does this. So far all I have learned is people throwing parts at it with no definitive answer on what is causing this.

 

Did you replace the thermostat or not? The stock thermostat is 187 degrees F / 87 deg C. When you checked the codes was that before or after you reset the ECM by removing the battery ground cable?

From the Factory Service Manual here are some things that might help:






Checking IAT issues is more involved and covers a lot of pages in the FSM. Since the issue seems to be intermittent I would check the wiring and connectors going to the IAT 1 and 2 sensors to make sure it isn't damaged or the connectors corroded or otherwise making poor contact.

Bill

 

Yes I did change the T-stat. Normally I use only AC delco parts but for some reason I brain farted and just got a napa replacement which I was told was 207º setting. I had gotten a replacement t-stat for my C6 which was an AC Delco part from my favorite parts house but this one was a napa brand and I didn't think about it till later. I can't tell if what I took out was an original part or if the previous owner put a cooler t-stat in. In any case, this new one gets really freakin hot, like spikes up to 217 before going back down to 206 and back up again. I'm thinking I need to look for another one with a lower opening temp. This one just seems way too high. Are these temps normal with the OE t-stat?

I never checked codes when it went into this failure mode, but there were no check engine lights on. And all I did was disconnect the negative terminal for a few minutes, and tap the brake pedal to release any residual voltage. Probably not needed but it was suggested to do that and its worked to reset the system so far.

 

Looked on fleabay for t-stats and pretty much mishimoto seems like the only game in town. In reading the descriptions it seems the stock temp is 212. The one I removed was a 207 but based on how the replacement 207 is operating the original was clearly stuck open. Mishimoto offers a 160 and 180. Seems like the 180 would be ideal for street use.

 

Just buy oem. All others fail quicker. Oem is 194 degrees. I’ve gone though 5 or 6 different types. From “brand “ names to summit racing cheapos

 

Per the factory service manual the stock thermostat opening temperature is 187 degrees F (see my post above). Before purchasing more thermostats test the ones you have using one of the methods I mentioned in my post. Coolant temp can go above 297 degrees (the point where the thermostat is completely open), thermostats only set a floor for the coolant temp which can vary depending on how you are using the engine and when the ECM turns on the engine cooling fan. Engine cooling fans are turned off at speeds above 35 mph since they would restrict air flow Vs enhance it. Driving on the highway at cruise control steady speed or 70 mph I will see coolant temp running between 188 degrees and 190 degrees and oil temps running from 188 to 192 degrees depending on engine load.

However, on track with the engine being used at max load or near max load coolant temps run just below 220 degrees and oil temps run in the 260s. These are all temps that are considered to be normal.

I suspect your problem is more than likely electrical and could be due to a poor electrical connection or a battery issue.

Bill

 

Thanks Bill. I will test the one I suspect has failed, but will most likely end up making a trip to the dealer to get the correct opening t-stat, and check it as well. I assume that the part of the thermostat that gets tested in water is the small flanged brass pellet assembly that is pressed into the plastic housing with the spring?

I really think its a slow to heat up condition as every time its happened its occurred early in the drive and the air temp was fairly cool, around 50 degrees or so.

On another note, has anyone had the expansion tank cap come apart? I wanted to check the coolant level and the cap cover separated from the male part of the plug? I have managed to get that stuck in the reservoir. I can turn it counterclockwise but it doesn't want to back out. I'm pretty sure whats left is gonna get destroyed during the removal process.

 

I returned from a road trip today. 500 miles and everything was perfect. I was sweating bullets on anticipation of it happening again. My car came up to temp properly every time. I dont think I am out of the woods yet....