I'm looking to hook up a water temp gauge and want to tap into the upper radiator hose for the sender. It looks like the hose has different diameters from one end to the other. Has anyone spliced into the hose with an adapter like is shown in the very bottom of the picture and most importantly what adapter diameter did you use?

 

You'd be better served to put the sensor in the hottest part of the engine - the cylinder head - that way you'd get a more accurate reading of the water temp. I think putting it in a rubber hose is a mistake, it will leak............

 

MINIdave, you don't just put it in the rubber hose. You replace the plastic piece that houses the bleed valve with another that has a 1/8" npt threaded into the top to put the sensor. Yes, putting one on the block drain would be better but that drain is inaccessible without removing some parts (like the starter).

One other thing about putting it in the top hose is that you probably won't see any change in temp until the thermostat opens.