I have an 83 fxrs, with a custom made oil tank. I would like to add on oil temperature gauge to the bike but not sure where to put the sensor at. I think having it in the oil reserve tank is pointless, and I'm not a big fan of drilling into my case either to install one. Any suggestions? I was thinking of buying a 3/8 adapter with a 1/8 npt and putting the sensor inline with the oil return from the oil pump.

 

in a time that has passed we had installed them in the oil return line to the tank from the engine

BUT I was never a fan of part blocking the oil flow - reason most put a dip stick with the temp gauge in the end

 

Every one of those mechanical temp gauges I've seen eventually leaked and the electronic ones get kinda clunky with the sender unit.

 

You never add to the oil feed side but it's OK to add things like an oil cooler or temp gauge to the return line.