Coolant depleted without any visible leaks

Yeah, leasing the truck changes the dynamic significantly. I would still weigh up the cost of just buying coolant to keep running. You can get the concentrated coolant that you have to mix with water for about $12 a gallon at Walmart. A gallon of distilled water is 89cents also at Walmart. That's 2 gallons of mixed coolant for $13.

How much coolant would you have to go through before it stopped making financial sense?. I can't answer that as I don't know how much you are using...or how much you would lose with downtime at the dealer who will have no qualms about charging you hundreds of dollars to tell you they can't find anything either.

 

If the cap is the culprit, there will often be vertical trails from it left by the drops trickling down the outside of the reservoir. And sometimes the leak can be stopped by flipping over the gasket on the underside of the cap.

 

A cap is cheap enough that I would just buy a new one and replace it. It's a lease truck do your shop would probably just take that money out of your maintenance escrow or whatever.

You would be kicking yourself if you went to the dealer and they found that to be the problem.

If a new cap doesn't fix it at least you can tell whoever that it isn't the problem...and you also have a spare cap for your parts box.

 

My truck was doing something similar in that it would drop to minimum then stay there for a while before it got low enough to cause low coolant warning.

I just got into the habit of checking the level at the start and end of each driving leg. 30 seconds to drop the hood and eyeball it soon became second nature.

 

You mention it's a freightliner, but what engine?. Do a basic Google search for coolant issues with that engine. That may turn up ideas/ YouTube videos of places to look.

 

Check around the water pump. That's where mine was leaking. Not enough to drip on the ground as the fan was blowing it back on the engine where it dried up. It wasn't until I told the shop that I saw dried up coolant in that area that they figured it was the water pump.

I suspect the shop mechanics just do a simple pressure test and don't spend time actually searching for leaks.

My truck had the Cummins X15.