That is the area where the heat exchanger is located, and yes the water temp gauge is right there as well. I would think that know matter what you do, it will be a messy job removing it from the engine. You have both engine oil and ATF to deal with. I recently noticed mine has a very slight leak at the fitting, I suppose from the recent trany work, I am going to tighten the connection from below, when the weather cooperates, hopefully this will take care of the problem.