kap1

I've searched this forum and appears only a few threads. I got CEL, went to local garage for OBDII scan and came up P2181. The coolant seemed just below max line so he added some and reset. Fine for 10 days then CEL again. No coolant leak, its actually still above the max line slightly. On start temp gauge stays bottom and goes up to about 1/4 after 10-15 min of driving. I live in NJ, this happened on first cold day. Also, I read something about it being caused by missing belly pan. Mine actually is missing (snow last season), just bought OEM replacement and will install soon at oil change.

I understand P2181 is yet another common problem but many different views on real culprit. Consensus seems to be thermostat. I'd rather not pay $100 dealer charge for VAG scan plus $700 to replace thermostat. My plan is to have thermostat replaced by a good indy shop that will stand behind it ... my fear is what if I do that, spend $500, and CEL comes back ? in the B6 A4 does P2181 have any other cause ?

Any thoughts/guidance much appreciated.

Crash Craddock

Thermostat is a really easy job, no need to outsource
Do you replace the water pump when you do timing belt?

John535is

Is the engine actually overheating or are you just getting the code?

3 possible options to consider.

If it is a bad water pump, the engine will run from cold, then just keeps getting hotter and hotter. The thermostat will open when the water is at the normal temperature. Without the pump, the gauge temperature will now rise (depending on outside temperatures and how fast the air can get through your radiator, then it will raise sharply as it boils the water out. High risk of head distortion at this point. Loss of water, hot steam, all a mess.

Sticking thermostat is very similar symptom to failed water pump, sometime you may see the temperature go higher than centre on the gauge, then it will come back, go up, come back. This is the thermostat opening irregularly and needs replacing until it actually just stays stuck one day and looks like the above scenario.

If you are not seeing any of the above, if the engine does not appear to be boiling (you have no loss of water to indicate this) then it could just be the sensor gone bad. This is actually the best scenario because they are cheap ($15-$30) and easy to replace, and it's a DIY.

The sensor is located on the radiator hose. It has the large plastic clip that you can slide out with a flat blade screwdriver so you don't need special tools. If you leave the blue cap on the expansion tank done up tight you don't even loose much water when you remove the old one. What you do have to check is whether its a grey sensor (2 wire) or green sensor (4 wire). You may need to unclip the electrical connector (which is black), check the colour of the plastic on the sensor or count the pins to confirm you order the correct one. Takes 5 minutes to replace, no special tools.