Boyd,my experience it's both models. Look for it in the water hose coming up from the oil cooler before it reaches the top of valve cover, should be a bracket that surounds it & keeps it from vibrating. But due to this site I've become aware that Isuzu configured similar vehicles very differently around the globe, sometimes even in the same country, ie; my turbo has no EGR (thankfully!!) while another claims it was standard? Maybe no oil cooler means no thermo-valve!? If your rig runs OK, doesn't run too cool (is that even possible in that "humididity"?) I wouldn't lose sleep over it.