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Discussion Starter #1
I've had this V6 G8 for a few months. I've been eyeing these cars since the first year they came out and could finally afford one. About a few weeks ago the car overheated briefly. Was able to shut off the car immediately and coast to a parking lot to avoid any damage. I have coolant and haven't lost any, radiator fans work as they should, no blockage on my radiator for air flow, no noise from water pump and no leaking. I was thinking thermostat might have stuck or the radiator cap wasn't functioning as it should. I started cheap and replaced the radiator cap first to see if that fixed the issue. So far no overheat. But my temp gauge does move to the line I marked on the picture occasionally (I know I need to clean) for a few seconds then goes back down to operating temp. Radiator fans do kick up on high before this happens (the gauge doesn't move every time the fans are blowing on high) and it's only in stop and go traffic after driving a while. The miles are rounding 150K so I want to replace my themostat, water pump and possibly radiator anyway for preventative maintenance (I had a sunfire a while back that gave me cooling issues constantly so I get nervous). I do catch a faint whiff of coolant occasionally. The smell is burnt into my memory from past cars. But I can't find a leak anywhere. Only thing I can think of is I'm getting the smell from coolant going into the overflow and some of the smell comes from the weep hole in the reservoir. I'm rambling a bit but I guess my question is, is this a normal for the temp gauge to move that far? I understand there may be some floating, but I didn't know if the gauge moving up a full quarter was normal.
 

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Discussion Starter #3
Exactly. I could see it maybe going to the halfway marker if it moved at all. But getting to that point makes me a bit nervous.
 

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Regarding the odour, mine seems to have a small leak above the water pump...I think from a seal where that tube with the pressure cap attaches to the head/block. Might be a similar spot on yours.
 

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Discussion Starter #5
I've been watching it and driving it a bit after posting. When the coolant is going back into the reservoir, there's a tiny bit pooling up where the fill neck connects. I'm thinking about just sealing it with some silicon or rtv.
 

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I had the problem at the filler neck, there is an O-ring in there that split and replaced and haven't had a problem since.
The coolant leaks from the O-ring and pools and/or runs down the valley towards the rear of the engine making it look like the t-stat housing is leaking. I replaced damn near everything in the cooling system until we tripped over this.
Can't remember what it cost but it was not an expensive fix.
 

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Discussion Starter #7
I pulled the neck off and there isn't an o-ring present. Do you know if I could buy the o-ring by itself or did you buy a new reservoir? Been doing a little digging and it seems to be a pain to get to the thermostat housing with it being on the back of the engine. I can change it myself though. The coolant looks a little dirty so I'm just going to do a complete drain while I'm at it.
 

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The o-ring was done at a GM dealership, they had the o-ring in stock.
Just to be clear I'm talking about the o-ring on the coolant filler neck on top of the engine not the filler for the reservoir.
Yeah GM mechanics cringe when they get assigned A G8 V6 t-stat housing.
Always a good idea to change coolant anyway, I don't know how many jugs of coolant between what I added and the dealership added over the time this took to diagnose....you could eat off mine its so clean.
 

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Is the replacement radiator cap a Genuine AcDelco? Since the coolant looks a little dirty, try doing a drain, "flush", and refill. Unless the water pump is making a growling sound which is indicative of a bad bearing or leaking, then presumably it's "okay". In rare cases, the impeller separates from the shaft causing the car to consistently overheat due to a lack of coolant circulation. Is the heat emitted from the air vents hot, warm, or cool? Be sure to thoroughly burp the coolant system before replacing the radiator.
 

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Discussion Starter #10
Thanks for all the responses. I'm about to head to the parts store for a few things. Going to drain the coolant and replace the thermostat. After doing a ton of reading I think the most trouble I'll have is removing the windshield cowl. I found a thread on here so I dont break any clips. I'll take pictures and update.
 

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Until you verify whether or not the o-ring in the coolant filler neck on top of the engine is leaking I wouldn't be doing the t-stat/housing.
I changed literally everything coolant related under the hood, probably for nothing as they were not the problem.
The leakage from the o-ring dripped down thru the plenum and the intake, ran down the valley onto the back of the engine contaminating everything in its path making it look like it was the t-stat.
At one point they where convinced It was the head gasket because it was wet from the coolant running down the valley.
They had actually removed the plenum and the intake to start doing the head gaskets when they found the valley full of leaked coolant which lead them to the o-ring as bring the one and only problem.
My two cents FWIW.
 

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Discussion Starter #12
Yeah I get that. The coolant pooling up there isn't my main issue though. It's the temp raising too high. A few weeks ago it actually overheated.
 

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Discussion Starter #14
I finally have the thermostat replaced and everything put back together. I ran it for about 10 minutes and let it get to operating temp. Everything looked good until I got down the road a little bit. Temp kicked up pretty high but didnt overheated. I'm currently trying to work out any air bubbles that might be in the system. I dont have any leaks and my coolant levels are fine
 

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Discussion Starter #16
Ok. So after about 9 hours of work. Thermostat is replaced and coolant system is air free. I bought a funnel/attachments to aid in getting the air out. Ran the car for about 20 minutes and watched the temp gauge and funnel for bubbles. Drove for about a hour and the gauge didnt even move that I could see. I took a few pictures for reference for myself. This one was pretty exhausting.
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Yup, no onions here either. I paid to have it done.
You seem to have the tools and knowledge to have pulled it off, I have to say I'm impressed.
I can see your valley is dry so I apologize for pushing the o-ring agenda.
 

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Discussion Starter #20
I was actually talking about the reservoir pooling on the top. I see what you were talking now. It looked dry on the top of the engine. Lots of words were said during this job. If anyone has any questions about the tear down. Feel free to ask.
 
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