This problem affects pre-2000 chassis and has to do with the placement of the radiator fill on the header tank mounted over the radiator core.   With the filler neck mounted halfway up the header tank the most that you can fill the tank is to the bottom of the cap sealing flange.   When the cooling system is heating up and the water is expending all that happens is the air in the top of the tank compresses and nothing goes out the overflow pipe to the overflow/coolant recovery tank .   This prevents the system from purging the air out of the system and drawing coolant back into the header tank to prevent oxidation in the system.   Also because of the placement of the low coolant sensor halfway up the header tank the warning light on the dash is constantly going on whenever the vehicle either sitting with the front right hand low or when turning left at highway speeds.   The cure for the problem is very simple.   Put the filler neck on the top of the tank, or put a bleeder, with a short extension as an air collector, on the top of the tank and a sign telling the operator to purge the system by just opening the bleeder, complete with overflow line, when the coolant is at temperature until the air is expunged and then the recovery system will start to function like it is supposed to work.

Here are the pictures of my radiator modification.  The bleeder valve in the picture was from a first attempt to correct the problem without changing the set-up but to no avail.  It is not necessary for the modification.

So far, Freightliner has not acknowledged the existence of this problem.

Submitted by Dennis Uphill