I seem to recall that there are two engine temp sensors on a 2388. One displays the engine temp on the gauge on the A pillar. The other one is an interlock for the header. This way if your overheat the engine, it will disable the header, and not just kill the engine. It allows you to idle back the engine, keep the oil flowing, and cool it down. However, if the sensor goes bad, you might have this symptom without actually overheating.
I'm not saying that is it, but something to check out.
-Lance