Low Coolant Warning


New member
Nov 10, 2022
I have a 2018 Denali Sierra 2500 with 6.6 that just turned over 100k, and it just gave me a low coolant warning a few days ago. I topped off the coolant in the tank and it was fine for a day or two, now its back. In troubleshooting i was able to see liquid dripping from a 90 degree angled black pipe on the lower part of the firewall left side (standing in front viewing toward rear) down below the DEF fill pipe and below the coolant tank. Sorry i don’t have a picture of the pipe but i actually thought it was the air conditioning condensate drain pipe.

So i ran the truck and got down beside the passenger side front wheel and was able to catch some of the liquid in a cup, by this time there was a pretty decent flow coming out (fast drip) every 2 seconds. The fluid was colorless, odorless and tasteless, it did not have an anti-freeze taste so this confused me.

I honestly expected it to taste like anti-freeze and to find out my heater core had gone out. So any ideas, could this still be the heater core gone out? My floor board is not wet on the passenger side, i didn’t check the drivers side.

Anything else i should check?

Since this truck isn’t that old, that seems odd that a heater core would go out that fast, could it be a hose that connects to the heater core? Also how hard is it to get to this thing, i know on some vehicles you pretty much have to pull the dash out.

thank you


Well-known member
Jun 23, 2009
TX of course
I would advise getting a pump and pressurizing the cooling system to try and find the leak. You can generally borrow them from auto parts stores. If you don't find a leak you could possibly have a headgasket or EGR issue.


New member
Nov 10, 2022
I turned off the a/c and let the truck run for 30 minutes, nothing came out of the pipe, then i turned on the air and pretty quickly started getting fluid coming out of the pipe.

I know that i am smelling coolant From somewhere and hopefully its not just paranoia and what is the likelihood that all of a sudden i am getting a ton of condensatation (i guess with right humidity/temp combination it could happen). I’ve noticed the a/c condensate draining before but not quite this much.

I guess that there is not a problem with my heater core since there was no fluid at all coming from the pipe or anywhere else while running my heater.

I did top off the radiator coolant tank again and didn’t notice any decrease in the level yet. I’ll try to post a picture of the pipe but i cannot find any coolant leaking from any other location.


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Why do I keep doing this?
Staff member
Apr 19, 2008
Mid Michigan
Thats the AC drain. You have an issue somewhere else to cause lost coolant

Also, I moved this into L5P section...
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New member
Jun 21, 2020
I just started having the same Low Coolant alarm come up repeatedly. There are no leaks and all Tanks are full. My understanding from other posts and searches is that the issue is a bad sensor in the upper tank and that the sensor cannot be replaced without replacing the tank.

Then, I've also seen in another L5P post that there is a Tech Bulletin on the issue. Has anybody seen the Tech Bulletin or can direct me to it? I guess the question really is, "does the Dealer do anything as a result of the Tech Bulletin" or am I living with the alarm or replacing my tank at my cost and time ?