I am tracking down an overheating problem in one of my vehicles, and it was recommended that I check coolant temps directly to rule out a malfunctioning dash guage. I'm wondering which testing device I should get:

Here is the first example:
http://www.testequipmentdepot.com/fluke/thermometers/62.htm

From my understanding, this will measure the surface temperature of the
radiator hose. I wonder how much heat is lost between the actual
liquid, and the outside of the hose? I've found other
pyrometers/thermometers that have a submersible probe (such as this:

http://www.testequipmentdepot.com/tif/hvac/7000.htm),

which I assume would be more accurate, but more of a hassle to use, if not perhaps impossible, since you could not properly seal the hose to the fitting,
and would thus have water/steam all over the place?

Anyone?

Thanks

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1987 Mercedes 300D ~200K (Greasecar & Biodiesel)
1993 Ford F-250 7.3 IDI diesel 165K (Biodiesel)
1996 Thomas/International Bus with DT466 engine