How do I read the coolant temperature gauge?

well your power was not enough to have units in car's gauges

Unless you have shitty alloy heads, hitting the red for a second isn't going to kill your engine

>how fuking hard would it be

Gas tanks are not perfect cylinders. Therefore a drop of one inch in volume may be 1 gallon or 4 gallons depending on the shape of the tank. Sure you could map specific volumes to depths for a readout, but that would be way more complicated that the simple linear resistor in most cars today. So added cost and complexity.

Because of said tank shape, the fuel sender float doesn't actually move until some fuel has been used. So basically from Completely Full -> float movement is all guess work. Could be half gallon could be 3.

Gas sloshes around as you drive. Therefore your gauge may jump from 3 gallons to 10 gallons as you drive because of the aforementioned volume differences. You may already notice this if you park / drive on a steep incline. Jumping needles tend to scare most motorists. A linear resistor tends to smooth those movements.

i understand what you are saying but i cant believe it is that cost prohibitive to come up with a reliable system to read gas tank volume.
there must be some way

>integrate load cells into fuel tank mounting bracket
>load cell signal to PLC
>PLC translates output to desired unit of liquid volume
done.

Oh, so your poverty-tier poor, got it.

i've driven my taurus in the red once for like 5 minutes before i noticed the gauge, the fan controller was dead. no damage on the engine, gotta love cast iron

Pretty much this. on a 2012 chevy express the gauge sits in the middle and it says 210 but plug it into a scanner and it reads 204 at most. Once it gets up to temp most if not all sensors just stand still until it reaches a threshold of too cold or too hot to let you know there might be an issue but to not worry you most of the time if there isnt one.