In Reply to: 601 water temp gauge sending unit posted by Richard NY 2N on April 24, 2018 at 09:13:14:
Those are usually brass or bronze, so about the only tool that won't tear them to pieces is a deep-well 6-point socket. I have had better luck removing everything with a socket, with the old gauge fitting nut still in there supporting the adapter. In that case, I've already decided to replace the gauge and cut the gauge line out of the way. If there is no way a socket will fit, the next best tool is a flare-nut wrench. I've still destroyed a few before they came out. Thankfully, the fittings are softer metal than the engine block, so cleaning the threads isn't too hard. There is a set of crows foot wrenches in my box, but can't remember if I ever successfully used them for anything.
The next challenge is getting the new gauge line to fit. I believe the way those go together is an adapter fitting goes in the block. The adapter creates a place for the flare on the gauge line to seat. Some aftermarket gauge lines will not thread into the original adapter, and the new adapter won't thread into the block. Some adapters that seem to fit, do not provide a place for the flare to properly seat and seal. The 601 may be slightly different, but I've run into similar problems nearly every time I was putting a new gauge on an old machine.