Re: How hot does your diesel run?
The important thing to remember with temp gauges is that they may not be an exact reading of the true temp (off even 10 or 15 degrees), but the changes are very significant. For instance, once the thermostat has opened it should come up to a normal operating temp (usually 180ish) and remain there. If the temp fluctuates w/ a change in RPM's, dropping at lower RPM's or rising as you go up, you have a cooling problem. If it begins to creep up (not in a day but over successive trips) from whatever is the normal operating temp, your impeller has probably lost a few vanes.
After a bit of time you will have a good idea of your normal operating temp reading on the gauge and can keep an eye out for changes. Your engine should run at the same temp for half an hour or 20 hours; time should make no difference.
There are odd times, usually in extreme conditions, where the engine is working much harder than usual and the temp can go up a few degrees, but it should never go above 200 (from 180ish), no matter what. I hope you also have an audible alarm, because a plastic bag or something else could cause a blockage in the line and the temp will go up very quickly to damaging levels, unnoticed on the gauge.
"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.