According to google, a propane flame is around 1900 C (3452 F). The flame shoots into a tube that is 57" long and I am trying to monitor the temperature of the tube at the opposite end of the flame.
I do know, it maxed my little thermometer out at 600+F degrees but I have no way of really measuring.
Do they make a thermometer that will work with the arduino that will measure this high of temperature?
There are several types of inexpensive thermocouple probes that can be routinely used at temperatures up to 2200 F, and more expensive ones that go quite a bit higher.
The temperature you quote is at the very hottest point of the flame, which is not particularly relevant for measuring heater or furnace temperature, let alone exhaust gas temperature.
Bare metal probes don't pick up much radiant heat having very low emissivity, although that does
increase with temperature. Forced air circulation will give good heat conduction to the probe, but
you have to be careful that enough of the wire upto the probe tip is all in the air flow so that
you don't get too much heat conduction along the wire, perhaps an inch or so.