Going to look at a 6.4 today. What's the most important thing to look at? I have a scan gauge to read some PIDS. A thing
Anything in particular? This is the first 6.4 I'm looking at it, after debating on a 6.0.
Scan gauge will help with most things. If you can read coolant and oil temps make sure they are pretty close to each other. Check for leaks EVERYWHERE. Underneath, top of motor, bottom of motor, and check the blow by. Steam/smoke is normal just make sure it isn't a lot of pressure. If they have service records available get those. And also a carfax or oasis report would be good to look at
Ask the owner about regen cycles. If they are close together then the DPF is most likely a little clogged and/or he could be doing a lot of city driving so it doesn't get the chance to clean out well which chokes down the motor a little.
Check the amount of engine hours too. That will tell you how much idling the truck does.
Ask about routine maintenance done on it (oil, fuel, air filters, etc). The 6.4s are really picky about maintenance.