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Discussion Starter #1
Hey guys,

In about 7 hours, my family and I are hoping to hit the road for a 1K mile round trip in my wife's 210K 2000 Passat. B/c the temp has been wonky the last 12 months or so (usually hovers around 110 on the gauge), I decided to install a new coolant temp sensor and thermostat this afternoon (both decent German replacement parts). Guess that was a bad idea. On the test drive just now, the gauge seemed fine (locked on 190) for the first 5 mins then quickly went right up to the 260 and told me to "STOP!" I was a little low on coolant so my test drive was to the all-night WalMart to get some. (Please don't give me grief about the G12. I've been running Ext. Life Prestone after a flush for the last 4-5 years just fine.) I was just 1/2" below the MIN on the tank so I doubted that was the cause. I topped it off and sure enough, barely get 2 miles down the road and it sweeps to 260 again. I just limped it home.

The lower radiator hose is cold to the touch. The top one is fairly warm. It was a total PITA, but I'm 99.9% sure I put the new stat in right, but the only thing I can think of is I put it in backwards. Or, what else would cause this problem? Surely not the temp sensor??

Please help. I'm pretty much thinking to get us on the road in the morning, I've got to go put the old stat back in and continue to live with the messed-up temps.
 

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Discussion Starter #3
Hmm... I suppose I felt some rather strong hot air in the cabin even though the heater was off (wife had it dialed to hot).

I ran it for a good while without the cap on the coolant tank after installing the new stat. How do I bleed the heater core? I'd certainly like to try bleeding before breaking down the stat housing again.

Would air in the heater core cause a cold lower radiator hose?
 

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After trying a heater hose/core bleed and not finding much - if any -bubbles, I figured it just had to be a backwards stat. So I dug it out again. Sure enough. Installed it backwards. Can't believe it. Could've gone to bed around midnight. Instead, just now hitting the hay at 5am and have to be up in 2 hours for an 8.5 hour drive. Lovely. Stupid is as stupid does.
 

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After trying a heater hose/core bleed and not finding much - if any -bubbles, I figured it just had to be a backwards stat. So I dug it out again. Sure enough. Installed it backwards. Can't believe it. Could've gone to bed around midnight. Instead, just now hitting the hay at 5am and have to be up in 2 hours for an 8.5 hour drive. Lovely. Stupid is as stupid does.
That's harsh. I'll have to be real careful when I do mine.

Tips? Going to be using this guide probably:
How to replace your thermostat (AEB) - AudiForums.com
 

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This is a timely cautionary tale for me, since I am preparing to replace the coolant on my 1.8T. Since the thermostat has to come out anyway and is 12 years old, it does not make any sense for me to put the old one back in.
 

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(Please don't give me grief about the G12. I've been running Ext. Life Prestone after a flush for the last 4-5 years just fine.)
I won't. I used the same Prestone in our Passat for a few years until installing a Blauparts TB kit, which came with a couple of liters of Ravonal G12.
 
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