Originally Posted by kenfoozed
De-rate... I assume this means that it enter a sort of "limp mode"? If these engines de-rate and shut down, how is it possible to cause damage by overheating them?
engines can over-heat quicker than they can de-rate many times.. they often wont totally shut down, and believe me.. unfortunately there are people who keep running them till they do quit running..
de-rate means that they will slowly reduce the amount of fuel the engine receives, the hotter it gets.. this works when you have a somewhat functioning but overloaded cooling system, ie climbing a big hill and the fan clutch may not be fully engaged.. it slows you down and makes less heat, the cooling system can often catch up..
a catastrophic failure like a stuck thermostat, busted hose, or broken water pump belt will cause the temperature to rise way too quickly for a de-rate to do much good..
on most, the dashboard will alarm, normally the alarm is when it means shut-me-down-now! people will often keep driving "to the nearest exit" which in many cases is too late.. a couple miles can run you up 20 degrees or more over the alarm temp..
when I watch my gauges, a slow rise in temp will warrant me slowing down if it gets warm.. a quick rise in temp.. even if not in the red will make me take heed and look at other things.. when i had a recent idler pulley failure.. i saw my temp go from 192 to 207 in a matter of 1/2 mile.. noticed my voltage at 11.9 and knew id lost the belt or water pump.. so I put it in N and shut it down.. then turned the key back on, turned on my heater pump and all the fans.. which kept coolant circulating through the engine as i coasted down to see what was wrong..
ultimately keeping an eye on the stats while you drive is important.. you learn how your bus acts.. and when you see it do something abnormal. whether "out of range" or not.. you can take heed.