Manually checking coolant temperature

[coldweatherblue]

My M20 runs a hair over midline on the temp gauge. Last week on the interstate it climbed up near the 3/4 mark and I'm concerned about overheating. I have replaced coolant and bled the system. I am replacing the thermostat in a few weeks when I do the timing belt/water pump, but in the meantime am wanting to manually check the engine temp using the thermometer on my voltmeter.

I have a few reasons to suspect it may be a faulty gauge rather than defect in the cooling system. Reasons why I suspect the gauge:

1. The cluster was changed by PO.
2. The dash has to be "thumped" for the gauge to come to life.
3. The gauge reads around the 1/4 mark after the car has been driven less than a mile. My old E30 would take probably 2-3 miles to even get out of the blue.. Seriously the gauge starts climbing out of the blue after the car has been run for <30 seconds. The gauge does move around a bit while driving as well..
4. The fuel gauge is screwed up as well and when the car is filled up only reads 3/4 full.

I understand that there are some 7mm screws behind the cluster that could be loose. The SI batteries seem okay.

I want to get the car to halfway temp and open the hood and check the temp with my thermometer.

What is the best place to manually check the operating coolant temp? thermostat housing? What temp should correlate with a gauge that reads at the midway point?

Thanks

[dnguyen1963]

Buy a laser thermometer from Harborfreight ($30) and you can measure the temp to your heart content...wherever you want.

[I got it, yes!!]

lol, I used a meat thermometer in the overflow, was off by 3 degrees lol