Chevy Silverado and GMC Sierra Forum banner
1 - 14 of 14 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter · #1 ·
2018 Sierra Duramax 6.6 - I've been getting a low coolant warning message on the dash. The surge tanks is full, checking both when hot or cold. Is there a separated tank below that? There's a cap on the side of that one, between the tank and the side of the truck. It looks to be empty. What am I missing? I can't put any more coolant in the top surge tank. Thanks.
 

·
Super Moderator
2015 High Country Duramax
Joined
·
18,610 Posts
The coolant reservoir is separated into two parts.

The normal reservoir, which has your pressure cap on it and will be full all the time and the level will fluctuate a little when cold vs hot. That level is always checked cold (tank has full cold mark on it).

The other section of the tank is the overflow/surge tank. This will usually be pretty empty, to maybe half full. All depends, and I've seen them be usually mostly empty on many trucks.

However, the coolant level sensors are fairly know to go bad.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #3 ·
So do I add coolant via the cap on the side? The top overflow/surge tank is always full to the top and doesn't seem to pass coolant back to the normal reservior.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #4 ·
Or am I backwards in that the top is the main reservoir and the bottom with the side cap is the overflow?
 

·
Super Moderator
2015 High Country Duramax
Joined
·
18,610 Posts
Top is the main tank and the bottom is the overflow.

On the L5P trucks like you have, now that I think about it, I don't think they have any wording on the tanks as to the full mark. But basically it will be full to the top on the top tank with the black cap that has the yellow markings on it.
 

·
Registered
Joined
·
148 Posts
IMO, the problem is the level sensor in the tank. I saw a thread on a Duramax forum that pointed to that. And my buddy just had his reservoir tank replaced because of the same problem. After the tank was replaced, problem solved.
 

·
Super Moderator
2015 High Country Duramax
Joined
·
18,610 Posts
What does the whole tank look like?

Thats different than what I've seen on the l5p trucks I've gotten in the shop before.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #10 ·
Tom51 said:
I've seen a post that suggests that it's one reservoir with a baffle, but as you can see, the top part is full, very little in the bottom part.
And thanks for taking a look - much appreciated.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #14 ·
I'm the OP. The sensor in the tank was indeed the problem, and had failed. It's a part of the tank, so I replaced the tank. Part was about $100. Thanks for the replies.
 
1 - 14 of 14 Posts
Top