Article 19 - Loss of Coolant as the Result of Overfilling

TSB #1 - September 15, 1971
(1970-72 L-Series Trucks Equipped with Super Duty or Caterpillar V8 Engines and Radiators with a Single Sight Glass)

To avoid false coolant level readings and prevent the unnecessary loss of coolant as the result of overfilling, check the level in the radiator at normal engine operating temperatures. Add coolant only when the level of hot coolant is below the sight glass.

The L-series crossflow radiators with vertical tanks are more sensitive to permanent anti-freeze coolant expansion and contraction than downflow radiators with top mounted horizontal tanks. Radiators of the subject trucks have one sight glass located about 10" below the pressure cap.

Coolant level of a stabilized cooling system (coolant level 2.00" below radiator cap when hot) containing a solution of permanent anti-freeze, after an overnight shutdown period, can drop below the level of the sight glass. This level can be as much as 4 or 5 inches below the sight glass at temperatures near or below 0° F. These low levels represent normal coolant contraction from lowered temperature, and do not represent a loss of coolant.