2015.5 LML Coolant Issues

[deadliftdiesels]

Hello everyone, first post here.

I own a 2015.5 LML Denali w/ about 61k on the clock, recently the truck was fully deleted including EGR/cp3 swap/ezlynk etc. Shortly after driving the truck home i received a low coolant light and was told to expect this potentially as it is a common occurrence. I was then told to just top off the coolant and return a call if further assistance was required from the shop.

Now, fast forward 1.5 months later my coolant light came up the other day, I then followed the owners manual procedure for filling/purging the cooling system of air. After completing this procedure to no surprise i was still losing minor amounts of coolant with no signs of leakage from hoses/fittings or anything visible on the ground.

I do not believe the head gaskets to be an issue, as I have a non-stiff upper rad hose condition the following morning post driving the prior night, as well as no remnant pressure in the reservoir. Coolant has started pushing into the overflow side of the tank and is also appearing on the top of the reservoir as of now immediately after driving.

So my question is, could the potential culprit be the radiator cap or the reservoir tank itself? My ECT runs around 176-184 on the CTS2 as well, so i'm not entering an overheated state, and like i mentioned no visible coolant on the ground either.

Thanks for any and all replies, and my apologies for the long entry post. Thanks fellas!

 

[M.A.M.]

Hello everyone, first post here.

I own a 2015.5 LML Denali w/ about 61k on the clock, recently the truck was fully deleted including EGR/cp3 swap/ezlynk etc. Shortly after driving the truck home i received a low coolant light and was told to expect this potentially as it is a common occurrence. I was then told to just top off the coolant and return a call if further assistance was required from the shop.

Now, fast forward 1.5 months later my coolant light came up the other day, I then followed the owners manual procedure for filling/purging the cooling system of air. After completing this procedure to no surprise i was still losing minor amounts of coolant with no signs of leakage from hoses/fittings or anything visible on the ground.

I do not believe the head gaskets to be an issue, as I have a non-stiff upper rad hose condition the following morning post driving the prior night, as well as no remnant pressure in the reservoir. Coolant has started pushing into the overflow side of the tank and is also appearing on the top of the reservoir as of now immediately after driving.

So my question is, could the potential culprit be the radiator cap or the reservoir tank itself? My ECT runs around 176-184 on the CTS2 as well, so i'm not entering an overheated state, and like i mentioned no visible coolant on the ground either.

Thanks for any and all replies, and my apologies for the long entry post. Thanks fellas!

First thing I would do is do a coolant system pressure test. My guess is there’s a very minor leak somewhere, and it’s evaporating before it hits the ground, and so you don’t see it.


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[deadliftdiesels]

First thing I would do is do a coolant system pressure test. My guess is there’s a very minor leak somewhere, and it’s evaporating before it hits the ground, and so you don’t see it.


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Getting the truck pressure tested tomorrow morning, with that being said will this test just blast coolant out of wherever the leak may be if there is one- making it obvious?

 

[M.A.M.]

Doubt it. I think the system is rated at 20 PSI. You’re not losing it very fast, so you’ll probably just see some drips somewhere if that’s your issue.


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[deadliftdiesels]

Just incase anyone was wondering, if you are mysteriously losing coolant and you try the air purge procedure from GM- the issue is more than likely the Reservoir cap, don't buy anything other than OEM because one from advanced auto did not fix my issue but an ACDelco did.

I am now no longer pushing coolant into the overflow/losing coolant and it is holding pressure fine. Also if your upper rad hose is soft/no pressure in the tank in the AM it is not HG's in my circumstance Just FYI!

 

[AZlml]

Every 5-10k miles I have to top mine off after getting the low coolant light. Originally thought the water pump, did it at 80k. 55k miles later (45k of them deleted and tuned) I still mysteriously lose coolant with no signs of it leaking anywhere. Haven't pressure tested the cooling system but it's probably not HG's based on rad hose test. I might buy a reservoir cap just because and see if it solves it. If not i'll continue to live with it until something gives up the ghost..

 

[kiwilml]

I've had the low coolant light come on I think three times in 80k miles. At first I was worried but not really anymore. I can see a few drops every now and then from my upper coolant pipe but can't imagine it's leaking enough to have to add coolant every now and then. I've tried getting it to stop but just seems to seep a drop or two sometimes for some reason.

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[LBZ]

I’ve got an extremely low amount of leakage ghost coolant leak also. I can smell it, can’t see or find it. I thought maybe it was from where/when I tied in my espar hoses to the heater hoses but it does not appear so. Gonna try the rad cap thing and see what happens.