I am also interested in the answer to this question. I recently bought a 99 D 5.9 for $500 after my old ones's transmission went out. Now I know this one overheated because I happened past it one day and stopped to talk to a fellow D owner. It apparently started overheating turning into a small commuity and started knocking and shut itself off turning into the previous owners neighborhood. Fast forward about three weeks and I have the vehicle in my possession. Seems they fixed it to some extent before they sold it to a dealership, the old thermostat was sitting in the cup holder and the radiator has a seal under the cap. It also seems to be running very cool now, takes a while for the water temp to come up and doesn't come anywhere near as hot as my old D did, about 160 crawling through traffic after a long drive on the interstate and 140 on.Is there something wrong with our D's?

 

AMBLIN:

based on what you are telling us there is likely no thermostat in your truck, especially with it never getting above 160, if you open the system up and install one (a 180 deg stat is recommended for your engine) the temperature will come up to a more acceptable level

 

OK, in the mean time is it safe to drive the vehicle? It has been driven nearly 500 miles without issue...


Edit: apparently it is safe. Going to have to see how it does off the highway though, that temp jump when I'm in traffic isn't reassuring.

 

you wont hurt the engine driving it cold like that, however you may set off a CEL, and you will likely have lower mpgs

the temp jump in traffic is a pretty common occurance, thats why there are fans installed, to keep the air moving even then the truck is sitting still, it is likely that your fan isnt engaging properly, but that could be caused by the low temperatures your engine is running at since they are set to come on at temperatures as dictated by the stock t-stat

 

OK, many thanks shrpshtr325.