Chevy and GMC Duramax Diesel Forum - Reply to Topic
2017-19 GM T-K2 Platform Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

Thread: L5P Low coolant message Reply to Thread
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  Topic Review (Newest First)
01-16-2020 11:09 AM
hvtexskeeter Dealer "filled the tank" and solved the problem for a few months then light came back and they had to replace the whole tank with sensor. Now no issues in 6 months
01-16-2020 07:48 AM
Originally Posted by lexiontech View Post
Let me know what you think.

Head gasket.

Let'em do their thing.
01-15-2020 08:07 PM
lexiontech Hey new to the forum but have been a lurker for quite awhile now. My 2019 L5P has been giving the low coolant warning consistently for the last two weeks. Every time I check it the level is fine, actually loosened the cap a couple of times but never took it off because coolant would start coming out the overflow. Even though it is always full to the top of the tank the message comes up every time you start the truck or shortly after and it will come on after clearing it also when driving. I was bringing it in to have the block heater update done and had them look into it, told them I thought it might just be the sensor as it was full every time I checked. They called me back after having it for half a day and said I have a bad head gasket. The truck has 27K miles on it! I asked if this is why the level indicator kept going off and he said yes, but was not sure if the tech had to add any coolant or not. Service writer says they performed some test that it failed, and by failing this test it limits the problem to a head gasket, nothing else it can be according to him. Well they said I could drive the truck for now because parts are 2 weeks out and they are out of loaner vehicles at the moment. They said they want me to come in and swap for a loaner as soon as they get one in. I did some searching but did not find much for the L5P's and head gasket issues other than one guy who had a catastrophic failure, and one on this forum who had the light come right back on after having the head gaskets replaced. Im not too excited to have my truck tore apart for a month. I checked the coolant after work today, it was COLD -14F ambient temp and truck had been sitting for 11 hours. The coolant level was a couple inches below the fill neck but still plenty high up in the tank. I felt the upper hose and it didn't feel like a tennis ball but was firm. Removed the cap and there was some pressure that released, I added about 1/2 quart and that brought the level all the way up to the fill neck. Started the truck with the cap off and let it run for a bit, didn't see any bubbles coming up but the tank started to slowly overflow as the truck warmed up so I put the cap back on. Low coolant message wasn't on at first, but came on as soon as I put it in gear and left my parking spot. Got home 3 miles away, checked level again still OK. Restarted truck and message came back again. Im not sure how a head gasket would cause this message to come on when the tank is full? Maybe there is something I am missing but if the tank is full, the message should not come on unless you have a faulty level sensor or wiring. Let me know what you think.
12-14-2019 11:08 AM
robrides Final word on my leak was, no leak. They did go ahead and change the coolant reservoir and sensor and got that covered by my extended warranty. The leak I had on the drivers side turned out to be the upper oil pan seal, covered under manufacturer's power train warranty. 38K mi on it at the time.
11-19-2019 12:33 PM
nasdaqinvestments I have this issue currently, the dealer has burped the system twice and it still comes on randomly but quite often. (about every 2 min) fluid levels are good so they are ordering a new res bottle and sensor and said that should fix it. The strike seems to be hampering their ability to get parts as I have been waiting 4 weeks and still hasnt come in. It's quite annoying with the coolant warning popping up all the time on the DIC
11-18-2019 07:55 PM
MIkey52 Don not mix different types of anti freeze. The wrong combination can turn it into jello.
11-17-2019 11:05 AM
Craddock01 I have an 18 Duramax L5P and recently got the low coolant message (35k miles). I checked the level and the manual states as long as the level is at or above the bottom of the arrows, all is good. My level appears good but I still get the message. I was going to top off which is what brought me to this forum. The manual mentions to only use DEX coolant but I've read some bad things about DEX if any air gets into the system. What is the general opinion about DEX. I tend to be skeptical when a mfg. recommends to only use "xxxx" since "xxxx" is usually 30-50% higher $ and sometimes not worth the extra $.
11-01-2019 03:45 PM
robrides My 2017 has gone low on coolant 3 times in 31500 miles. Took it to the dealer yesterday for this and some other issues. Got a call today - 'we couldn't find a leak'. I sent them pictures I took when I changed the oil this past weekend as well as the gm-techlink article. Mine is leaking on the driver's side of the engine but I couldn't see from where exactly.

According to the article they are not supposed to pressure test the coolant system.
08-31-2019 03:47 PM
Chevrolisle My 2016 3500 had a low coolant message while pulling 12000lb camper. It maintained normal temp. All said and done, had the heater hose replaced. Leaked around the clamp, (high on the engine) slow leak thankfully. $325 i was rolling again. But I did get a low coolant message the next 2-3 times I drove it. Topped it of and we're good....I hope
02-13-2019 07:03 AM
kiwi lml
Originally Posted by Suncatcher89 View Post
Had low coolant warning come on second day having the truck. Took it to dealer. They said it needed burped and some sensor computer work. It worked for about a month. Warning came back on and I told dealer. They said wait couple weeks should go away. It never did. Actually became more frequent. So now truck is at dealership and they did a pressure check on cooling system that failed. Now they are pulling all the glow plugs to test each cylinder. I hope it is not a head gasket. If so this will be a major problem.
Yeah but you don't have to worry about it, they'll fix you up like new if they are a competent dealer..
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