You aim the laser light beam directly at the sending unit base. Or aim it at the thermostat housing. Its fast and has a digital readout.

If you could talk your wife into using it in the kitchen too, the cost might be justified! :-)

Did you check the thermostats that were currently out of the vehicle on your stove? You would use a standard meat thermometer for that. Put them in a pot and slowly bring it to boil. I hang the thermometer on a kitchen tool attached with a rubber band. This puts the end of the thermostat about in the middle of the water for an even measurement. As you hit 80c (180f) watch the amount of opening. Your thermostat may not be opening enough. My experience is that the Wahler opens more than the Behr.

Leave the coolant in the car, I don't want to be responsible for a disagreement between you and the misses. :-)

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)