After replacing the old temp sensor with a new green top, the engine takes at least a half hour to warm up....acts like an open T-Stat, and it throws code P2181 now, as well.

Could I have introduced air into the system during the sensor swap, causing the T-Stat to stay open...are there any other possibliities? I did los some coolant and replaced it with the G12, per spec.

 

Aren't you the guy that lost the retaining clip during the install?

 

I am that guy!

 

beachchair- any advice....?

 

Your problem shouldn't be related to the new temp sensor. I wonder if the old retaining clip is somewhere in your engine causing a problem. It could be a faulty sensor. If you still have your old sensor, put it back, and see if that corrects the problem. Be careful with both the retaining clip and o-ring.

 

The old retaining clip popped off and went for a ride inthe engine compartment. It is not somewhere "in" the engine......how could that possibly happen, when the retaining clip has to be removed beofre the sensor can come out.....I am assuming you think it may have slipped in the sensor orrifce?

Reason I asked about air in the system, is because I saw a similar posting on another site

 

How many miles are on your TT?
What model and year TT do you have?

P2181 can be the coolant temp sensor, and/or the thermostat.

Edit: Almost forgot... Did you replace the O-ring when you installed the new coolant sensor?

 

55K mmiles on an '04
I did replace the O-Ring as well

 

Well, it wouldn't be uncommon if your water pump and thermostat needed to be replaced.
It's about time for your 60k timing belt service. Might want to look into it!

 

Still a curiosity why the T-Stat would stick open after the sensor swap... don't you think?