Strange smoking problem

Those temps would be normal if it's running in 1/2 mode. Try the test again, but chock the wheels and release the brakes. That will tell you if it's set up to run in 1/2 engine mode with the brakes set.

Many fleets set them up to run in 1/2 engine mode when cold. This helped them warm up a little faster and have less smoke. But once the brakes are released, it goes to all 6 cylinders. The 3 cylinders should alternate. One time it will run on 1, 2 & 3. The next time it goes in to 1/2 engine mode, it'll run on 4, 5 & 6.

 

Hang on, when I was having that problem I remember someone at Detroit telling me to check the heater core because it mimics a bad head gasket. I had a 1999 classic xl with a s60 straight 500. But yeah there is some kind of pressure test they do but for the life of me I can't remember it's been like 10 years.

 

Injector seal. Re do them all lube them before putting them in with whatever is safe for that kind of rubber or go online and find the silicone ones for super high pressure. Generally in expensive. just time consuming.
and google the heater core thing or ask a dealer. even detroit corporate can be helpful sometimes.
By chance this thing over heat or freeze with watery coolant in it?

might be a crack around #1 in the head gasket, head or both. look for white crusty hard stuff on your injector tips if you end up pulling them.

 

Yup, but depends on who they are, cutting corners and such. also some can be defective.