Hoping to provide a write up on calibraiting/adjusting a mechanical temp gauge (water or oil temp gauge, as long as its mechanical).

I had noticed by temp gauge was not dropping all the way down after the engine was completely cold. Pic below of the gauge with the truck off, sitting in a 60deg garage not having run in over 16hrs. no way that engine is 120deg.


I had a new gauge at the ready just in case, so brought both of them inside for some testing. Old gauge on the left reading about 15deg higher than the meat probe on the stove (gauge 150, probe 136), and the new gauge is just a hair low (132deg), but more accurate. So what now?!


Because this old gauge fit the hole in my dash (new gauge was too small) and I had the new gauge already as a back-up I thought what the heck, lets dust off the old Marine Engineering degree and break into this gauge to try and calibrate it.
The process is quite easy although know this going in: any adjustments are very sensitive.
If you ever get the chance, after you pry open the gauge pod, you bend this little arm in either direction until the needs aligns with the known temp that the probe is in. And I mean SMALL adjustments. It can feel like you haven't moved it at all and the needle will have moved 20deg. careful careful!.


After about 3mins of that I had it damn near dialed in!
The critical part is to check calibration at the temps you expect it to operate at to make sure its accurate when/where you need it to be. Bending that tab may slightly adjust the change-rate of the needle (how quickly it moves from say 100deg to 150 might be ever so slightly different to how fast/slow it changes from 150 to 200deg.
I checked mine at 180, 190, 200, and most importantly 210. All of them fell within one needle's width of my cooking thermometer. Happy times.


Throw it back together and off you go! no fear of inaccurate temps again!
A fun little project if you ever get the chance. and a relatively easy/cheap thing to replace if you break it. Go on live a little!

 

Even easier if a person is using the factory gauges since they were made to be adjusted without opening them up completely.