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Discussion Starter · #1 ·
I have this code that keeps coming up on my car. It is P2181. I posted about it a while back when I replaced my coolant sensor.

As it says in that thread changing the temp sensor seemed to work for a while but now the code is back. I bought a device called an ELM327 bluetooth adapter on eBay for $15 and an android application called Torque for $5 (thread about that here). I used those things to read the freeze frame data. Here is the info:

Freeze frame information:
------------------
Engine Load = 43.529 %
Engine Coolant Temperature = 69 °C
Fuel Trim Bank 1 Short Term = -0.781 %
Fuel Trim Bank 1 Long Term = -0.781 %
Engine RPM = 2,574 rpm
Speed (OBD) = 107 km/h
Timing Advance = 27.5 °
Intake Air Temperature = 9 °C
Mass Air Flow Rate = 27.44 g/s
Throttle Position(Manifold) = 21.176 %

End of report.


I read the Rosstech info for P2181 and it says
Freeze Frame data stored with in the 68*C ~ 80*C range is an indication that the vehicle was close to, but not within, the cooling systems normal operation range. The Thermostat itself or Cooling system components may be at fault.
I suspect the thermostat. I read a good writeup on this board on how to replace the thermostat but for me it seems kind of daunting. Although if it comes down to that I'll do it. What I am wondering is if there is any other component I should check or more diagnostics I should do before attempting to replace the thermostat. Also what's the normal coolant temp for a Passat? My car is a 2003 Volkswagen Passat 1.8T AWM.

Thanks
 

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Depending on which engine you have, it can be easy, or hard. The 1.8t is pretty easy. The V6 is behind the timing belt so it will be harder. The W8 is tricky too, the intake manifold will have to come off...

You might also want to be sure you have flow from the water pump, but most likely your t-stat is bad.
 

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To see the thermostat housing, peer behind the alternator. You can see where the bottom radiator hose comes into the block. There are two bolts in the housing, requiring either a 5mm allen key or 10mm socket (combination bolt). It is tight but doable. Make sure to replace the o-ring as well.

When I replaced the thermostat from my 1.8TAWM, it looked like this:



It is from a car I bought that needed some TLC. Needless to say, I am doing a larger, more complete flush. Yours will probably not look this bad.
 

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Discussion Starter · #5 ·
To see the thermostat housing, peer behind the alternator. You can see where the bottom radiator hose comes into the block. There are two bolts in the housing, requiring either a 5mm allen key or 10mm socket (combination bolt). It is tight but doable. Make sure to replace the o-ring as well.

When I replaced the thermostat from my 1.8TAWM, it looked like this:
Thanks I found the thermostat housing I think.. pic attached. Good lord is that thermostat disgusting. I hope mine doesn't look like that. I'm at 90k miles. If this nice weather holds to the weekend I'm going to change the thermostat then. Here's the related thread with the DIY:
DIY B5.5 1.8t Thermostat replace
 

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HAve you done the timing belt yet??

If not I would just do it and the water pump, tensioner etc.. at the same time.

Also when you have the tstat off reach around the inside towards the front of the engine to get a feel for the impeller of the w.pump.
Most factory ones are plastic and sometimes they come apart/come off of the shaft on the pump and just free spin.

If the t.belt hasnt been done you need to do it.

If it has just feel that impeller while you have the tstat out.
 

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Discussion Starter · #7 ·
Well that all looks very complicated to do. I don't mind doing things like that if I have very clear concise directions on how to do it for my specific model. Right now I think I'm going to stick to the tstat but I will feel the impeller. Is there any other symptom that presents itself when the impeller detaches or has broken apart? Coolant temps seem to be ok once the car has started. That top hose is always burning hot though. I assume that's how it should be.
 

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The timing belt on an AWM was not difficult to do. Put the front in service position (talgentix DIY does fine as a guide) then start removing stuff. It will take 6 or so hours on a weekend to do and you need a good assortment of torx drivers, metric sockets and allen wrenches.
 

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Well that all looks very complicated to do. I don't mind doing things like that if I have very clear concise directions on how to do it for my specific model. Right now I think I'm going to stick to the tstat but I will feel the impeller. Is there any other symptom that presents itself when the impeller detaches or has broken apart? Coolant temps seem to be ok once the car has started. That top hose is always burning hot though. I assume that's how it should be.
Water pumps can fail in 2 distinct ways. The impeller can breakdown and reduce the coolant flow which can lead to overheating. Worse though is the rarer situation where the impeller shaft can seize, which can rapidly lead to a timing belt failure....
 
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