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low coolant warning, surge tank full to top

low coolant warning, surge tank full to top

Postby Tom51 [OP] » Sep 15 2020, 11:37pm

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.
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Re: low coolant warning, surge tank full to top

Postby 19trax95 » Sep 16 2020, 12:10am

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.
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Re: low coolant warning, surge tank full to top

Postby Tom51 [OP] » Sep 16 2020, 12:17am

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.
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Re: low coolant warning, surge tank full to top

Postby Tom51 [OP] » Sep 16 2020, 12:24am

Or am I backwards in that the top is the main reservoir and the bottom with the side cap is the overflow?
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Re: low coolant warning, surge tank full to top

Postby 19trax95 » Sep 16 2020, 12:31am

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.
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Re: low coolant warning, surge tank full to top

Postby DrPepper » Sep 16 2020, 1:04am

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.
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Re: low coolant warning, surge tank full to top

Postby Tom51 [OP] » Sep 16 2020, 2:54am

Both caps are black with yellow lettering. The one on the side (lower reservior) indicates the pressure cap at 20psi.
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Re: low coolant warning, surge tank full to top

Postby 19trax95 » Sep 16 2020, 3:02am

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.
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Re: low coolant warning, surge tank full to top

Postby Tom51 [OP] » Sep 16 2020, 4:36am

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.
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Re: low coolant warning, surge tank full to top

Postby Tom51 [OP] » Sep 16 2020, 4:38am

Tom51 wrote: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.
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