This bulletin applies to 2010-2014 Chevy Express and GMC Savana models that feature an upfit with rear heaters, such as ambulances or buses. When filling the cooling systems, ensure that the rear heater is purged of all air.
Some vehicles may have the rear heater mounted higher than the coolant bottle. Some rear heater units may have been fitted with a shut-off valve and/or coolant pumps. It may be necessary to contact the vehicle upfitter for a procedure to make sure that the rear heater is flowing coolant and all air is purged.
One suggestion is to drive the vehicle through several thermal cycles after performing the Vac-N-Fill procedure.
While driving, make sure that there is coolant flowing through the rear heater system. Monitor the coolant level in the surge tank before and after each thermal cycle and add coolant as needed.
When the coolant level in the surge tank remains constant before and after the drive cycles, all air should be purged from the system.