X15 Cummins coolant problem

I’d do a combustion gas test on coolant. That’s where I’d start.

 

I have had two T680 trucks with the x-15 engine and both consume coolant more than any other engine I've seen. After driving for a day I usually need to add at least a half gallon of coolant. I consider the maximum fill line to be the minimum fill line in reality and even the guy at my shop usually overfills the reservoir knowing it will consume the extra coolant no matter what.

I have ran into the issue that you are experiencing when it over consumes coolant while you're driving. If you remove the radiator reservoir fill cap after the coolant is warmed up it will depressurize the system and throw the sensors off to the point to where you could just fill the whole thing up completely and the low coolant warning indicator will still go off. Once you turn the truck off for the day and let it take some time to reset itself the next day everything should be fine.

 

Some places put vacuum on the system by using the radiator cap. They do it to suck out air pockets. I dint know how much that equipment costs but it's an idea.

 

Fill it to max line and see what happens. Not minimum.

On another note. The last x15 i drove needed some type of seal in the pistons. What i was told anyways. But I was losing a gallon and day that eventually went up to 3 gallons a day.