Under heating and cooling fans at max

mbalbritton

mbalbritton

#@$%!
Joined
Mar 22, 2005
Location
Lakeland, FL
2014 GMC Sierra with 5.3.

Started out this morning and made it about 20 min up the road. Heard my cooling fans running at max and my temp gauge is not registering any heat. Pop the hood and it’s dead cold underneath. I’m in Florida so air temp is about 50 degrees.

Suit engine off and fans keep running. On off on off gets the fans to stop. Otherwise I have to pull the relays to get them to shut off.
 
Coolant temperature sensor. They default to full fans when the sensors shat the bed as a fail-safe. I've messed with two of them for guys at work in the past couple of months. Usually an easy fix!
 
mbalbritton said:
Fixed… but not before dropping both the old and new sensors down into the abyss of the engine bay never to be seen again while laying across the engine bay with my finger stuck in the sensor hold holding back coolant like a little Dutch boy on a dyke. 🙄
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At least it ain’t as bad as the oil pressure sensor
 
Faulty sensor they make them in quantity not quality anymore. Best to put on oem parts if you can afford it they seem to last better than aftermarket parts at least it does for me.
 
LT1JEEP said:
Faulty sensor they make them in quantity not quality anymore. Best to put on oem parts if you can afford it they seem to last better than aftermarket parts at least it does for me.
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FFS, the Napa one was $50… for a fucking sensor!

I just want to make sure something else couldn’t be causing the failed sensor.
 
mbalbritton said:
FFS, the Napa one was $50… for a fucking sensor!

I just want to make sure something else couldn’t be causing the failed sensor.
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A sensor is a sensor. They sensitive to extreme temperatures (mainly heat), debree on the connection points, fluids getting past the seal, and vibration. So assuming your sensor is not subject to any of these, then your best bet is to blame china child labor
 
These days, I won't even bother buying sensors from parts stores. I'll buy Delco, Delphi, NGK, or NTK off of RockAuto and wait a few days just so I don't have to do them twice. Anything I've gotten from Advance/CarQuest, AutoZone, or OhReally's? will usually crap the bed again. It's the unfortunate reality in which we live.
 
Dumb question, but is it out of coolant?
 
Ok… WTF? Going down the road and all of a sudden temp gauge is registering again. Albeit registering low at about 185. But it’s not bottomed out as it was this morning and 2 min earlier.

Also to note, the AC wasn’t working at the same time that the sensor wasn’t working. Now the AC is back on with the sensor working. Maybe part of the fail safe system though.

But WTF is it working now or potentially intermittently?
 
mbalbritton said:
Ok… WTF? Going down the road and all of a sudden temp gauge is registering again. Albeit registering low at about 185. But it’s not bottomed out as it was this morning and 2 min earlier.

Also to note, the AC wasn’t working at the same time that the sensor wasn’t working. Now the AC is back on with the sensor working. Maybe part of the fail safe system though.

But WTF is it working now or potentially intermittently?
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AC not working is definitely part of the fail safe. Probably has another sensor somewhere that is getting a different temp reading than the one the gauge uses. If its too hot/high, the system won't allow the AC compressor to kick on. Maybe also if its too cold or has no continuity.

I had an issue in my truck where the coolant was low, but the stupid reservoir design makes it look like its 1/2 full. So I noticed the fans running in traffic, trying to cool the system, which was only showing like 205 degrees, but I also had no heat. The actual coolant flowing through the system was extra hot, because it was not enough volume to properly evacuate the heat, but also I had no heat in the truck because there wasn't enough liquid in the system to pump up to the heater core. Topped it off, fixed the leak, and everything was back to normal. I'd double check your coolant levels just to be sure its not something like that. If the gauge sensor is not contact the coolant because the levels are low, you will get weird readings.
 
jeepinmatt said:
Probably has another sensor somewhere that is getting a different temp reading than the one the gauge uses. If its too hot/high, the system won't allow the AC compressor to kick on. Maybe also if its too cold or has no continuity.
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A LOT of computerized vehicles utilize multiple sensors, Example: ECT... one for the ECM *only* and another for the dummy lights/gauges...
 
jeepinmatt said:
AC not working is definitely part of the fail safe. Probably has another sensor somewhere that is getting a different temp reading than the one the gauge uses. If its too hot/high, the system won't allow the AC compressor to kick on. Maybe also if its too cold or has no continuity.

I had an issue in my truck where the coolant was low, but the stupid reservoir design makes it look like its 1/2 full. So I noticed the fans running in traffic, trying to cool the system, which was only showing like 205 degrees, but I also had no heat. The actual coolant flowing through the system was extra hot, because it was not enough volume to properly evacuate the heat, but also I had no heat in the truck because there wasn't enough liquid in the system to pump up to the heater core. Topped it off, fixed the leak, and everything was back to normal. I'd double check your coolant levels just to be sure its not something like that. If the gauge sensor is not contact the coolant because the levels are low, you will get weird readings.
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Not sure how else to check the coolant levels as there is no cap on the radiator and the only access is the reservoir (or resistor :D ) and like I said, it's full.
 
mbalbritton said:
Not sure how else to check the coolant levels as there is no cap on the radiator and the only access is the reservoir (or resistor :D ) and like I said, it's full.
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As long as you're sure its full, nothing to worry about. It's just the kind of thing that is so obvious its easy to overlook.
 
I've worked one a few of those and two of them got a second sensor before they acted normal. I will usually put a new thermostat in them too.

Not much to burping them, really. Fill it up, run it, thermostat open, and fill it the rest of the way up. Unless there's a bleeder screw somewhere. Then use that also. It's been a minute since I was under the hood of one.
 
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