Ford F-650 Owner's Manual page 190

Maintenance
The use of correct oil viscosities for diesel
engines is important for satisfactory
operation. Determine which oil viscosity
best suits the temperature range you
expect to encounter for the next service
interval from the following SAE viscosity
grade chart.
E163370
187
I n f o r ma t i o n P r o v i d e d b y :
F650750 (TBC), enUSA, First Printing