paul 56

Hi All,

Twice now on the way home my radiator fan came on, and stayed on long after engine shutdown, even though the engine temperature on the digital gauge was indicating only about 165F, Both times the analog engine temperature indicator was pegged at the lower limit as if it had no power (the needle was working normally earlier in the drive, and I did not see when it dropped to zero). The radiator fan would not shut off until I disconnected the battery. After reconnecting the battery the car operated normally with both engine temperature gauges agreeing to whatever the engine temperature was at the time. I have read on this forum that the cause for the extended radiator fan running could be either a faulty thermostat or a faulty engine temperature sensor. I don't think it's the thermostat because the engine temperature is normal according to the digital temperature gauge. Also, my problem is intermittent, with about 20 drives between the two events. I was thinking it must be the engine temperature sensor because the analog temperature gauge was pegged at the lower limit. So here's my question: Does the engine temperature sensor supply the information to both the analog and digital engine temperature gauges? If that is the case, then the engine temperature sensor is not the problem, as the digital temperature gauge appears to always be working normally. The problem would be somewhere between the sensor and the analog gauge, and I'm thinking the fan controller might also be somewhere in there. I was hoping for a quick fix by replacing the engine temperature sensor, but I'm concerned that it won't fix my radiator fan run on after shutdown problem, because I always have a good digital temperature indication. Any knowledge about this condition would be greatly appreciated. Thanks!

Red86Cfour

Long story short, change your thermostat. Its either opening too quickly, or its stuck open. If it doesn't heat up to a certain temp in a certain time, the ecu assumes the temp sensor is bad, so it goes into overheat prevention mode. AC and rev match (if m7) controls are locked out, and the fans will run full blast long after shutdown. Digital and analog temps will read zero. The fans will immediately turn on at cold startup. Short term fix is disconnect negative for a minute or two to reset the condition and return things to normal, but it will happen again when the temps are low and you drive long enough. Once you replace the tstat you'll notice engine temps around 215.

paul 56

Thanks Red86cfour! What's odd with my car's condition is that the analog temp read zero, and yet the digital was still reading the normal 165F. I'm puzzled why they both did not read zero. Also, I've owned my car since new, almost 8 years, and it's always run at about 165F when cruising. I think my car is one of those that GM put the 165F thermostat into during the build. I'm also thinking that I should put in the 190F thermostat, as my car does have the reduced redline showing on the tach while cruising, even after driving 30 minutes or more.

DoubleG

Wow, sorry I'm not knowledgeable in this field other than what I've read in the past, but you should not have a reduced redline after 30 minutes of driving. It's possible the tstat has been faulty since new, but I would replace the tstat if only to raise the engine temp some. Then go from there.

Nice write-up. I appreciate your clear explanation. Sorry I don't know what supplies info to the analog gauge.

Red86Cfour

I noticed that after one or two additional drives even the digital would go to zero. You might not have driven it enough to get it to go to that mode., I'm not aware that gm put 190 degree thermostats in them, though thats where mine ran when I got it with 38K on it. When I replaced it if I remember right it had a 217 degree stamp on it, and the stock oem temp is also 217 according to the dealer. I was surprised. But after the swap thats exactly where the temps are now. It was about five years old when I swapped it out so changed the coolant at the same time.

paul 56

Thank you!

paul 56

Thank you!

Grand Slam

You might want to investigate the proper thermostat for your car. Looking online I see C7 thermostats as low as 160. Others, including here, suggest 215. The AC/Delco GM thermostat is 195 which is what I just had put in my car after having the same problem as the OP. In cool, not cold, Northern California my engine temp now runs consistently at 195 or slightly higher.

paul 56

Thank you!

Red86Cfour

What year? My dealer said it was 215. I'd feel better running 190. Different part number?

Grand Slam

^^^ I have a 2017 GS which means dry-sump if that makes any difference. My shop ordered the GM thermostat. I don't know the part number.

We could not see a temperature or part number on the failed thermostat but I think it ran in the 195 range before it failed.

Red86Cfour

Mine is a 2014 Z51 so dry sump also. The thermostat I got definitely had a temp stamped on it 215/217 can't remember now, but for sure not 195. Perhaps if it fails again I'll inquire about later year like 2017.

paul 56

I'm the OP for this thread. I replaced the original thermostat in my 2016 Z51 with a Duralast 90 degree C (194 degree F) thermostat. It was the only one I could find locally, and I didn't want to wait for a shipped one. The factory original thermostat that I took out looked good, and had NO stamp on it to indicate what temperature it was built for. I will repeat that in the 8 years I've had the car since new, the temperature has always been around 165F while cruising. My new thermostat has the car running at 194F while cruising, with no redline reduction, so I'm happy. If replacing the thermostat has not fixed my problem with the fan continuing to run after shutdown and the analog temperature gauge indicating zero, I'll be back with an update, and will probably look at changing the temperature sensor next.

Red86Cfour

I think your problem will be fixed. I changed my sensor first and the problem came back the next day. tstat replaced and problem gone.