unless you have taken some time to precisely calibrate them to a "master" gauge/thermocouple, and this CAN be done, you are just playing tiddlywinks.
if it doesn't steam like a freight train, or puke coolant all over the ground when shut off, it ain't hot.
I'll agree
With some saying coolant /air flow, try increasing the RPM to 1.5-2K. You will be generating more heat but also moving more air and coolant. it's another data point
EDIT: and is simulating driving down the road as far as water flow is concerned, less heat will be generated as the motor is not under a load, HOWEVER more heat will be trapped under the hoodI "start" getting nervous with a know accurate reading until 220°. The general rule is 230° is the danger point and exceeding that may lead to internal damage and that it will definitely occur by by 245°. There are a lot variables due to clearances, components used etc. How hot does a top fuel motor get by the end of it's 1/4 mile run?
I have always gone straight to a thermocouple which is coupled to a laboratory grade digital temp meter. The thermocouple is placed as close as possible to the t/sat and inserted directly into the coolant. One can get extension leads so the meter can be placed on the seat if desired. Many will use surface probes or IR guns. IMO, they should be used as an indicator ONLY as they are rarely accurate.
I have calibrated factory gauges (what a PITA). And as previously mentioned I have seen brand new "name brand" gauges be whacked out of the box. Both electrical and mechanical. Voltage and grounds can affect the electrical ones
Interesting tidbit, the gauges always seem to off on the high end and the warmer the reading the further off they are.
I do know from doing the factory gauges, there are two adjustments for the high and low reading. It may test your patience as the "pivot" point between the two is not in the middle. (Think off an offset center on a balance scale).
So adjusting one end, affects the other but not by the same amount
that's the patience testing part. I would imagine if one
does so on a regular basis they may develop a "feel" for it or they may be a piece of equipment that the gauge repair people know of.
The gauges are thermally activated by the current passing through the gauge windings. Should someone want to try this themselves, a small box with a clear face will be needed as any air moving by the area will skew the readings, ( IE: walking by, picking up anything off the bench etc.). This does not occur in the car as the gauge is inside the cluster
Allow 5 minutes or 1/2 a beer between adjustments for the gauge to "stabilize"
