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Discussion Starter · #1 ·
So I'm new to the diesel family as a owner. I just bought a 2005 GMC sierra 2500hd Durmax lly. I love the truck it's in near perfect condition, 118000 miles on it, single owner an older guy who towed a camper I'm assuming because it has helper springs and a 5th wheel. So since I bought it I involuntarily noticed that the temp would go up to 220 or so once then shoot down to about 140 (on a cold day down to about 50 - 80s) then it would jump between 160 and 190 usually. I never thought much of it but one day I jumped in and drove like 400 ft to a shop across the street to talk to someone and when I shut it off I heard like a monster roar from under the hood and I was getting out of the truck wondering what that was and then the sound went away and I heard liquid peeing I went around front and saw the coolant was just peeing out of the over flow tank. I thought oh that's werid did it over heat? I went back and turned the key to on and the temps were below 100. But that bad chicken leaked out a good gallon before it stopped. So about a week later after noticing that sound more but no coolant leaking(never added any from when it leaked), I had went to my uncles shop and this kid that worked there said oh yeah bad head gasket and walks right over to the overflow tank and takes that cap of like there's no possible danger and that thing I tell you geysered like no tomorrow he got absolutely covered and just goes yeah see. My uncle who is 25+ year ASE Certified mechanic. Disagreed due to the trucks lack of millage and the fact that I told him it doesn't overheat and it truly never does. It's winter now and she 90% of the time doesn't make heat. I've found out that it won't leak out antifreeze and make that sound if I run the truck up to temp where the thermostat opens then if I park and shut it off no sound and with no sound no over pressured overflow tank no leaking.

So things I first though a bad thermostat (obviously start with the cheaper option to a head gasket) so I replaced them both and I just did it quick I watch a small part of a video about where to put the 2 holes and such so I did that and really no change. So my uncle said try to get some UV dye for the antifreeze and see if we can find a possible leak else where but that was unsuccessful due to if I filled the antifreeze and it was ran before the thermostat opened then it would come out the over flow tank while driving witch evidently put the UV dyed antifreeze everywhere so that didn't work. So I would just run with the overflow cap unscrewed, just set on the top and I wouldn't leak anything and if I shut the truck off before the thermostat opened it would be a loud roar then gone. Being winter it really sucks with no heat so my uncle and I were doing some digging and I found a video about how to replace the thermostats so I decided to watch it I read about possibly a bad new set of them and in watching at the end the guy takes off the bleeder bolt on the thermostat housing before adding antifreeze and I was like oh boy I didn't do that! So I hoping that it was my issue bought 2 more and did everything in the video to the T and for once in owning the truck I had solid heat! And the truck temp stayed between like 178 and 182 never moved a whole lot and that was something new to me I had never seen it do that. But that was short lived (I had the cap screwed on after replacing the thermostats) the next day I had ran to the store and back and when I shut it off it made the sound and started leaking. So I knew it wasn't the thermostat ( I knew before but I hoped)
I ended up buying a head gasket test kit to put on the overflow tank. Well the blue fluid on the tank quickly turned to green in about 6 or 7 pumps. This was done after I replaced the thermostats the first time, the second set was to hopefully have heat and prolong fixing it till more spring time, but that didn't work.
The coolant line is never hard at any point that I've touched it. It doesn't over heat. The coolant doesn't change colors or get dirty. The only time I've seen the temp get to almost 260 is if I have the antifreeze tank full 1 and 2 the cap is screwed on tightly, the truck will stay cool 60 - 80s then it will sky rocket fast but it goes way up once then the thermostat opens and it's back down like nothing and I can punch it and it won't go back that high after the first time.
I have found that when the cap is on tight and tank is full at idle is doesnt really leak but if I let the high idle go on it will leak a steady stream but once I turn the high idle off it stops,, so I assume the low coolant reading comes on after filling it is because when driving it just leaks out. It's confusing.
I had my buddy (he owns a 2004 durmax) in it about a month ago and from what he was seeing it do he said that it could be that the head gasket could have a tiny crack allowing the piston to allow it to overpressurize the antifreeze causing that loud roar. Everything he looked up came back to thermostat. He had recommended to try to just remove them and see what happenes. I'm unsure about doing that.
So in short the truck doesn't over heat, Doesn't make heat. It has had the thermostats replaced twice. The coolant leaks if I don't run it up to where the thermostat opens. Coolant only comes out the overflow tank, that I've found. I've checked the oil weekly and it's black no milky water.

So I'm hoping posting this can help me figure it out a bit. My uncle and I were looking into doing the head gasket job, but he wants to talk to some people and see what they say for as much information as possible.
Thanks for taking the time to read my poorly put together rant of information I have.
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