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94 STS Overheating, Purge Line?

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Hey all, my 94 STS gave me a "Low Coolant" warning on Tuesday and then started to get hot. It was rising quickly compared to normal so I pulled over at around 220 at a gas station. I topped off the coolant and drove a couple miles before it started to get hot again. I let it cool, put some more coolant in it and got on my way again.

On the highway, the temp was all over the place. It was rising and falling between 200 and 235. My STS has always run rock solid at 201 so this was odd. After getting off the highway it started to overheat and I could see a trail of water behind me. After pulling over, it's clear that the overflow tank was just dumping coolant out of the overflow. Once again, I wait, fill it up and limp home the remaining 5 blocks.

I've been working on it after work this week and so far I've flushed the system several times. There was a lot of gunk and what not in my overflow tank so I figured why not. Next I replaced the thermostat which was missing a decent chunk of rubber on the inner gasket. It look like some had been sucked through. I bought a new water pump only to realize I didn't have the proper tool to remove the old one but it looked fine and I saw no leaks. It definitely seems to be pumping water.

Last night I buttoned everything back up and filled it up with coolant. Honestly, I didn't feel like it took all that much. Maybe 1.5-2 gallons which seemed low seeing as I know it was bone dry. I fired it up, drove around the block, let it cool, and topped it off again. Afterwards I did a highway test drive and it stayed rock solid at 199-201. Success right? Wrong. I stop at Chipotle for some long overdue dinner and on the way back the temp starts rapidly rising. Low and behold I have a trail of coolant following flowing out of the overflow tank.

So now my thought process is maybe my purge line is clogged and I have heaps of air in my system as it didn't take all that much coolant. My question is does anyone have a picture of this and where it attaches at both side? I want to pull it off after work tonight and see if it's clogged. I understand its attached to the overflow tank but where is the other attachment point?

Any other ideas? I know "headgaskets" is always the response with overheating on these Northstars but I'm not sure that's what my problem is. It seemed to be all of a sudden and I think the loss of coolant is due to a small leak on the backside of the engine, possibly the heater core. There's always been a small dripping sound on that side and I never really thought much of it. Need to get that looked at if I can stop this thing from overheating.

Thanks for the help in advance. This car only has one owner before me and roughly 140K on it. I know I'm definitely in the timeline for headgaskets but I'm hoping that's not the case. This car is in ridiculous shape for its age and rides like a couch. I'd love to keep it around for a bit.

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Disconnect the purge line from the surge tank and place it in the surge tank neck. Start the engine and there should be a steady flow of coolant out of the purge hose. If not, trace it back to the water pump crossover, disconnect it, remove the hollow bolt and clean it out.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Thanks guys, turns out part of the thermostat gasket had broken off and made it's way into that hollow bolt. Blew out the rest of the line and she's running fine at 199-201. Although I stopped at the gas station and left it running. It was at 208 when I got back to the car and promptly cooled off to 201 when I started driving. I don't remember that happening before. For reference it's only around 25F outside. Is that normal?

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