99 Freightliner w/ Cummins sig 600

Buying an old truck is a gamble. Hope you are lucky

 

Not any more of a gamble then a newer truck.

 

Find out if the previous owner did any regular sampling and if they have the reports still available. 1 oil sample can be informative but if they are done regularly it is much more informative as you can establish what is normal for that engine and spot patterns and future issues as they develop.

 

You could have a pressure test done that is pressurize the cooling system to 15 lb or whatever a mechanic suggests and let sit a while to check for any leaking head gaskets or pin hole in a liner then release all pressure start truck with pressure tester still hooked up to radiator and wait to see if it builds any excess pressure from a pin hole in upper part of liner or head gasket or? Pressure tester kits aren't expensive in fact I've always wanted one think I'll buy one myself good tool to have just one note the 99 Frtlnr has an air over electric bunk heater control valve which when it goes bad puts 110 psi into cooling system causing many a misdiagnosed cracked head costing thousands when all it is a$20 part. It only does it when the bunk reaches desired temp and the valve closes while it's open and flowing through no problem making it an intermittent nightmare so if you ever start blowing water out of overflow and keep having to add water and when you turn off eng with cap off it shoots out like a volcano 10 ft high!!! Turn off the vales to the bunk till you can replace the control valve good luck w truck I always wanted a 600 sig love the way the wiring is concealed gives it a nice clean look I remember the very first ones out had a problem runnin hot heard they fixed it can't remember what it was or even what year 97 maybe I ran w one the guy said bad fuel economy but it was powerful put my 425 cat to shame!!!