[prestadude]

I don't know how your 1988 is configured but on my coach, I would have to extend the slide to expose the radiator hose (for the infrared measurement suggested by Prarieschooner). The Newell manual warns against operating the generator with the slide open because the air flow pathway through the radiator is disrupted and the generator will ultimately overheat. So, I think getting the most accurate measurement would involve opening the slide and the then immediately taking a reading as it appears that the temperature will start to drift up with the compartment open.