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?

  • 1
    Not an answer, but maybe a direction change. Have you considered this information lives in the ECU already? OBD2 bluetooth connector and a popular phone app would give you everything you wanted and more without mod.
    – Matt
    Commented Oct 20, 2016 at 22:34
  • That is a good point, but the seller I bought the gauge from said that it would be a complicated process to find the right wires to splice into.
    – KFP
    Commented Oct 21, 2016 at 14:27
  • Yeah no splicing or anything with the OBD2 method. You do accept a few things though. Wherever the sensor is for the particular data you're after is where you're measuring the value from. In your case I think the coolant bypass on top of the engine is where that's measured. If you're after a specific location for a specific reason then obviously this doesn't work, but if you're ok with it (Subaru is good with it, good enough to build their car with that being the only sensor) it may be sufficient.
    – Matt
    Commented Oct 21, 2016 at 15:33

2 Answers 2


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...


I'd do all 3, and have 3 temp gauges: rad inlet, rad outlet and just before the thermostat. It would make troubleshooting a cooling problem a little easier.

Who needs a big empty dash anyways? :)


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