3.0 Duramax smelling anti freeze after parked

dguth66 · November 7, 2020

New 2020 Sierra with 5K miles (8K Kms) ..

Everything is running fine w/normal temps - no CEL etc, but once I shut down after an hour drive and walk around my truck a few mins after there has been a faint antifreeze smell at times but both tanks look to be at fill mark. Thinking it must be a slight hose leak or something .. I'll keep a close eye for now but checking hose connections is on my list .. wondering if anyone has had same question or maybe GM has alerted with a TSB ??

Sqrls · November 7, 2020

A faint smell of antifreeze on a truck that new is nothing to be alarmed about especially after an hour long drive. The coolant tanks have an overflow that allows vapors and excess coolant to come out, especially since it could have been a little overfilled from new. It could also be the smell of hot diesel exhaust pipes and/or DEF smell.
Anti-freeze contains an oil component to it so if you have a leak, it will leave oily residue behind. The best way to know for sure would be to check for oily residue or if you get a spot where parked that looks like water, but does not seem to evaporate like water then you do have a leak.

KARNUT · November 7, 2020

It would be unusual being it’s under pressure. Maybe ifs it’s over full, a big maybe unless it’s overheated. It would be considered not environmentally friendly these days. I always walk around the front of my vehicles after driving and would be concerned with any smells especially antifreeze. My two main vehicles have over 100K miles no antifreeze smells.

TweetybyrdRT · November 7, 2020

I've got over 15k on mine and still get the same smell when she gets warmed up. I wouldn't worry about it unless you end up with a puddle. my fluid levels have always been spot on. so I know I'm not losing anything.

i was told by many with more diesel experience than i that it's the Def making the smell, remember ours happens under the hood instead of further down the pipe.

jnissen · November 8, 2020

Yeah the DEF has a certain odor that’s similar. Keep an eye on fluids just to be safe.

dguth66 · November 9, 2020

Thanks for the feedback .. I'll keep an eye on the overflow tank levels as that will show what's happening in longer terms.

I've smelled that same smell many times before in the past (auto mechanic was my first career) and it has that distinct sweet component but hey I've been wrong before lol !

Must say .. I continue to be amazed on the capabilities on this unique powertrain but of course I've always been a GM / Chev fan

jnissen · November 9, 2020

Thanks for the feedback .. I'll keep an eye on the overflow tank levels as that will show what's happening in longer terms.
I've smelled that same smell many times before in the past (auto mechanic was my first career) and it has that distinct sweet component but hey I've been wrong before lol !

Must say .. I continue to be amazed on the capabilities on this unique powertrain but of course I've always been a GM / Chev fan [emoji4]

Yeah I’m amazed as well. Yesterday on a trip out to my ranch I got 37.2MPG. Was near ideal conditions but still amazing for a truck this sized.

Time2gofishing1980 · November 11, 2020

I have about 16k on my 3.0. I get the same smell frequently

dguth66 · November 11, 2020

Hey Thanks Joe thats good to know, hopefully it's something known about and GM has "checked off" thru testing.

We'll just have to keep enjoying the 3.0 in the meantime .. Cheers !

Kchampagne · November 12, 2020

23 hours ago, Time2gofishing1980 said:

I have about 16k on my 3.0. I get the same smell frequently

Me too!

dguth66 · December 9, 2020

Thanks Ken .. good to know, in my experience its not the norm but hey I'm always open so maybe it is for the 3.0

Time will tell I guess and the more we know the better

Tom Bagni · February 22, 2021

Easy fix i had the same problem of coolant smell inside and out.

out the side of the coolant tank drivers side is a pressure relief hose

just extend it to the front or down under the truck

I did mine at 12000 miles no smell since then 16000 on truck and of now

Barret Pace · June 23, 2021

ok so I just bought one of these, and I also get the smell, anything every come of it? mine is a 2020 with about 23k.

Also the temp seems a bit high (just over the 210 mark) is that normal? Thanks

bmatherz · December 31, 2021

2020 AT4 w/ 3.0 duramax. Same smell here. Started after rear main seal blew and was replaced at 17k. A week after this repair I started smelling coolant. Week later coolant leaking underneath by oil pan. Then the temps got to 225-250 today. Fan kicked on full blast and then stayed on after engine was turned off. Checked coolant and it was low.

overflow hose in tank might be sending coolant out and that’s why it’s dripping underneath but not sure .definitely low on coolant and causing to overheat. No chk engine light or temp warning lights tho. Back in the shop for second time in a month.

Luke L · January 24, 2022

2021 Sierra 3 liter AT4 10,00 miles, almost always smell coolant after it is parked. Found a couple puddles at 2000 miles and took it in and the dealer could not find anything and pressure testing didnt leak down. I only had a small puddle a couple times when it was run at 25 below zero and then pulled into the shop for the night. Puddle was found in the morning after it had sat overnight. My coolant overflow is almost empty again at 10,000 and it is going back in to the dealer. I put it up on my lift and you can see a coolant trail on the tranny cooler lines on the right side of the motor. The turbo is just above this location and I don't believe the dealer wanted to dig that far into it to fix the leak. Hopefully they take care of it this time.