onceover

I have a feeling that its not the preload on the flange thats causing it to be so tight. When you have dissimilar metals threaded together you'll get galvanic corrosion, and the parts will want to stick together. Has the car been driven in winter/salty road conditions?

And aluminum is a very good conductor of heat, which is why you're having trouble heating it up. All of the heat is transferring from the plug out to the case.

https://www.metalsupermarkets.com/wh...uct-heat-best/

cjoenck

You are of course correct and I misspoke. I should have said that aluminum is notoriously hard to heat up. Using an induction heater also doesn't help because it doesn't work (well) with aluminum. I don't think I am skilled enough to use a propane torch so close the all the non-metal parts in that area though.
Yes, the car has been driven on occasion in a Chicago winter. While I tried to rinse off any road salt, I am sure that area was exposed to it even briefly.
So question, is there a way to chemically losen the bond between the metals. It's funny because the drain plug is very different. It's the typical steel plug, aluminum washer affair with a small magnet just like the engine oil plug on the thermostat. I wonder why Porsche decided to use aluminum on the fill plug.