As the title states, I recently changed my head gasket ('99 420a). I spent hours and hours researching, posting my questions to the forums, and buying all the recommended parts*. I got everything back together and started the car.

It started great and idle was very smooth. It was rough before the head gasket change but I think that was just because the throttle body was full of oil. The car was sitting in a heated shop at about 55* and nothing visible was coming out of exhaust pipe. After about three minutes, vapor came out nearly as bad as before I changed the head gasket.

The smoke continued. I couldn't clearly tell if it was white or blue. It seemed like a pale blue but the shop walls are white so it's deceiving. Since the repair, the engine has been running for a total of 40 minutes idling and putting around at no more than 25mph with some slight revving to see the smoke level increase.

I did everything by the book for this head gasket change. I love the car and will keep it for a long time so no short cuts were taken!

From my preliminary research, I am considering a few scenarios: 1) problem with piston rings due to overheating before head gasket was changed, 2) coolant still sitting in catalytic converter and muffler but will vaporize after a few days of driving

I changed the head gasket because it seemed to be the problem to me, a shop diagnosed it as the problem, and because 420a's are known to kill head gaskets.

What is your advice? Thank you very much for reading this! I really appreciate the help!

* Because I know someone will ask, I used a MLS gasket with copper coat and replaced the head bolts which I torqued to MLS standards.