FSB 561-023

Mack Trucks, Inc.
Greensboro, NC USA
Field Service Bulletin
Trucks
This Field Service Bulletin replaces bulletin, "Air Compressor
Coolant Hose", PV729-FSB561-023_M (USA57609) dated
(07/2013).
Date
Group
No.
Release
Page
7.2013
561
023
02
1(1)
Air Compressor Coolant Hose
GU7, GU8
MP8
FSB 561-023, Air Compressor Coolant Hose
(July (2013)
On certain MACK GU8, and GU7 trucks with EPA2007 and EPA2010 MP8 engines (built from
03/11/2009 to 07/10/2013), the production air compressor coolant return hoses have the
same inside diameter (I.D.) on both ends of the hose. However, the fittings for the current air
compressor coolant hoses are not the same size at both ends. The incompatibility of hose ID
and compressor fitting size has caused the compressor hoses to come loose/blow out from
the air compressor fittings. Should a leak or blow out occur on one or both hoses, replace
both hoses and the clamps.
The existing hose (part number 21324084) has been replaced by hose (part number
22053195) to prevent hose blow out. The new air compressor coolant hose is designed to
accommodate a 12.3 mm (0.48 in) hose fitting at the air compressor and a 13.4 mm (0.57 in)
fitting at the coolant supply pipe with an overall tolerance of ± 0.8 mm (.03 in). Additionally, a
paint mark was added to the hose air compressor end to ensure correct installation. See
image below for reference and correct air compressor coolant hose orientation.
The existing longer coolant supply hose (part number 21324019) has been replaced by new
hose (part 21962870). The new hose has a similar inside diameter corrections to
accommodate the fitting size at the compressor end. The new longer hose does not have a
mark to indicate orientation. It can only be installed in one direction only.
For the correct installation, the existing hose clamp has been change to clamp (part number
992082). The new hose clamp is torqued to 3.5 Nm (31.0 in-lb)
Note: This bulletin does not apply to MACK Trucks Australia.
W5079577
PV729-FSB561-023_M
USA60616