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So i just replaced my tstat cause of a P2181 code. Did my CTS (coolant Temp sensor) first and now moved on to this hoping it will fix it.
Start off by opening the top of the coolant reservoir to release any pressure on the coolant system. Then remove the clip holding the the CTS on the lower radiator hose. Remove the CTS and drain the coolant into a bucket

Take the upper intake hose off and stick it under the front radiator hose so you can stick a socket wrench in there better


Once the hose is off you can get a good look right behind the alternator and you'll be able to see the tstat housing and top bolt

Stick in a 5.5mm allen socket to unscrew the top bolt. The other bolt is directly below the top one. Stick a flashlight through the top runner of the intake manifold to see both of these bolts better


Use a magnet to retrieve the loose bolts so you dont drop or loose one.
Once the housing is off, you will see the thermostat and the o ring. Pry the thermostat out with a smaller Flathead screw driver.



Once the old one is out, set the new tstat in place, and then put the new o ring in (The o ring is going to fit in loose so make sure it doesn't fall out). (edited 26Feb13 by JTS)

Once the new o ring is in along with the tstat, bolt the housing back on making sure the o ring is still inside on top of the Tstat and bolt the 2 bolts to i believe 8ftlbs
Toss the coolant back in and check for leaks
 

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Yes, that's an AWM. The CTS at the bottom is actually a dual thermal switch for the fan.

OP, please don't buy Fram Filters. Baby Jesus is sitting next to me bawling his eyes out. :poke: You can buy stock filters on line for $5 and change.


edit: Oh, and nice write up! :thumbup:
 

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I find it easier to drain the radiator using the drain valve than pulling the fan switch. The clip on the switch can be difficult to seat properly sometimes.

You contradict yourself on the O-ring. Make sure the thermostat goes in before the O ring. I also clean the housing with some fine grit sandpaper to get the rust out for a better seal.

You can also use a 10mm socket on a swivel extension to loosen and tighten the bolts. The allen socket can strip if the bolts are stuck.
 

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Sorry to revive an old thread guys. Should any sort of grease or anything be used on the o-ring to help it seal? I was told by someone to do so to prevent leaks, but have not been able to find any sort of backup evidence on the site.
 

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No grease or sealant needed.
 
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Think it's possible to skip the draining of the coolant and simply quickly replace the thermostat? Thought I read somewhere that a chip tuner was doing that in-house as their ECU upgrade required a different t-stat.

Any downside to this? Would air get in? I would imagine it wouldn't, and then I would only need to catch whatever leaked out while switching the thermostats and refilling the reservoir to the proper level with new coolant.
 

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There is no quick replacement of the thermostat unless you remove the alternator. You will leak a good amount of coolant and let air in the system.

An colder thermostat is not needed, but there may be a tuner who suggests it.
 

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I got the generic engine warning light this week on my 04 passat. Dealer says I have both a bad thermostat and a bad temp sensor ($450 fix). Seems odd that the thermostat is bad at the same time that the sensor that is supposed to tell me that the thermostat is bad is bad too. Car's a 1.8T 4motion wagon with about maybe 80K miles.

Does anyone have experience with what the PO said re: "...a P2181 code. Did my CTS (coolant Temp sensor) first and now moved on to this hoping it will fix it."?

Thanks in advance!
 

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There have been a couple of cases like that. The CTS may or may not have been bad, but the thermostat fails slightly open and the car reaches operating temp a little too slowly, setting the code.

$450 is pretty high for this work. At 80K you are also due for a timing belt change that would normally include a new thermostat. You are a bit too far, but I would do the whole timing belt job (and CTS) for $180 labor and you supplying the parts (about $260 at www.ecstuning.com).
 

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Thanks PZ. I had the dealer change the thermostat, figuring I was already in for a diagnostics charge and I could do the temp sensor if I needed to. They were sure the thermostat was sticking. Seems like all's okay now.

I've got a good mechanic for the timing belt. It's on the list.
 

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So far so good on the thermostat-only change (no temp sensor change) keeping the engine light off. Four months later all seems well. Well almost well. Either the new thermostat is leaking or the water pump is on its way out.

Looks like it's time for the whole timing belt, water pump and while-you're-in-there service.
 

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You don't want to drive with a leaking water pump too long. I had someone drive their car to my house to check a coolant leak. He had to stop on the way to fill up the coolant (less than 10 mile drive). Once I got it apart, I found the water pump seized and had started to strip a 1/4" section of the timing belt.
 

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Great writeup! I saw elsewhere that ppl were saying you have to remove the alternator for the thermostat, which I was not looking forward to...

I'll be doing this while doin my TB. And to clarify, do I put the thermostat back in, then put the O-ring in the housing, then re-attach housing? That correct?
 

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I have the P2181 code and replacing the sensor didn't help. I thought it did but its gotten worse since. My thread is here:
(P2181) Coolant Sensor Replacement - 2003 Passat Wagon 1.8T AWM

I have some questions here because I'm thinking about doing the thermostat replacement described in this thread.

I notice in this tutorial you have the CTS located on the lower radiator hose. Does that mean there's a second CTS in my Passat? I thought there was just the one behind the engine (see my thread for pics).

I've read the comments and I'm trying to figure out when the thermostat o-ring should go on. We want the o-ring to go in first or the thermostat to go in first?

Can someone post pics of the drain valve for the radiator so I know where to drain?

I remember doing a thermostat change on a Hyundai once and it was a PITA because air gets into the system. I remember having to squeeze the hoses to work out an air pocket where the thermostat was. How do you deal with that on a Passat? Does it automatically purge the air? Can you discuss more about how you go about reintroducing the coolant?

If we're draining the coolant wouldn't we be better off just buying fresh coolant? We're at 90k mi.

Thank you for your time
 

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To fill the coolant and evacuate the air, you need to back off one of the heater core hoses. It is marked, and there's a hole in it. Slide it off the fitting until the hole is open. Then unscrew the top off the resivoir, take out the three mounting screws, and hang it so it's higher than the heater hoses.

All this allows the air to escape as you refill the coolant.
 
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