Coolant depleted without any visible leaks

Replace your cap, they use a pressure testing cap not your cap, so that seems to be the point of failure

 

I had a coolant leak that left no visible puddle on ground etc. Just constantly got low coolant messages. Reported it to shop they did pressure test and found nothing. Ran like that for thousands of miles, just kept filling it up every couple days. It wasn't until the leak got bad enough to leave streaks on the engine block that they narrowed it down to the water pump. This was a Cummins which has a red painted engine and of course the coolant is red in color so that didn't help spotting the leak.

 

A bad EGR valve will gulp down coolant.

 

I have tried for several minutes to remember the models, but Navistar had a problem with their auto-shift transmissions sucking water out of the truck. It was fixed and most of those old tractors are off the road now. I know for a fact that USA-Truck had an issue with some of their first Prostars.

 

I don’t know. I just know if it’s disappearing it could be the EGR valve

 

I just kept a few gallons of coolant on the truck and kept filling it up so I could keep rolling. I already had it on record that I reported the issue to the company shop who then returned the truck back to me with no fault found. Not much more I could do then other than refuse to drive the truck which in my mind and would just create a whole new set of problems that would only cost me money in downtime or looking for another job.

I even paid for some of the coolant out of pocket rather than submit excessive receipt reimbursements that might cause the company shop to have me take it to the dealer. The money I spent on coolant would be miniscule compared to lost revenue sitting in a hotel for days only for the possibility of the dealer also telling me they couldn't find a leak.