I'm installing a water temperature gauge and I'm curious which is the best location for the sensor; in the radiator inlet hose or outlet hose? The inlet hose will give the hottest reading as the coolant is just coming out of the engine, but placing it in the outlet hose will tell me that the radiator is doing its job which I'm assuming would give a proper reading as well. So, which is the best location?
I would suggest neither - the best location is at the thermostat.
This is because, in a properly functioning engine, the thermostat shuts off most of the flow to the radiator while the engine is cold (to help it get up to working temperature quicker), so much less coolant is flowing through the radiator hoses - therefore you won't get an accurate reading until the engine is up to temperature.
I'm guessing that connecting it directly to the 'stat isn't feasible however, so I'd say to go with whichever hose gets you closest to it - probably the top one...