Cooling System, Cleaning
M-260-002
(February 2009)

Valid for
All Mack CXU,CHU,GU,MRU,LEU

Case description
The cooling system drain and flush procedures outlined in this service bulletin are recommended for cooling systems
in which the coolant has been contaminated with engine oil, diesel fuel, or if the system contains substantial amounts
of rust or sludge deposits.

Danger
Before working on the vehicle, apply the parking brakes, place the transmission in neutral and block the
wheels. Failure to do so can result in unexpected vehicle movement and can cause serious personal injury or
death.

Danger
Coolant is toxic and poses a risk of poisoning. DO NOT drink coolant. Use proper hand protection when
handling. Keep coolant out of reach of children and animals. Failure to follow these precautions can result in
serious illness or death. Dispose of coolant and any cleaning solutions in an environmentally safe manner,
according to state and local regulations.

Warning
Always wear appropriate eye protection to prevent the risk of eye injury due to contact with engine debris or
fluids.

Draining and Flushing
1. Remove the cap from the coolant surge tank and then drain the cooling system as follows:
CXU, CHU, GU7 and GU8 Models (US07 emission-compliant engines), use the coolant
extractor/injector tool (tool No. 2815-2V700) to drain the system through the fitting located in the lower
radiator tube or lower radiator tank, depending upon chassis model.
Note: As an alternate, the coolant drain hose (tool No. 9996049), can be used to drain the cooling
system into a suitable container. The drain hose connects to the quick-connect fitting in the lower
radiator tube or lower radiator tank.
Note: Effective January 1, 2007, CXU, CHU, GU7 and GU8 models were equipped with the quickconnect fitting in the lower radiator tube or lower radiator tank, depending upon chassis model, for use
with the coolant extractor/injector tool. On MP7-equipped MRU models and LEU models, the quick-

connect fittings, which were implemented into production September 2008, are located in the lower
radiator tube. MP8-equipped MRU models do not have the quick-connect fittings at this time.
For pre-US07 models (those models equipped with E7, E-Tech™ and ASET™ engines), and MRU and
LEU models manufactured prior to September 2008, open the drain valve located in the lower radiator
tube and drain the coolant into a suitable container.
Drain the system at the following drain points:
— Cylinder block
— Coolant pump on MP7 and MP8 engines (remove coolant conditioner or coolant filter and leave the
drain valve open)
— Transmission oil cooler (if so equipped)
— Heater core (by disconnecting the hoses)
2. Once the cooling system is drained, close all the drain valves (disconnect coolant extractor), reconnect the
heater hoses and then flush the system with a quality commercial cooling system cleaner such as Penray 2015
Twin Pac Off-Line Cooling System Cleaner. Follow the instructions provided on the package.
Note: On vehicles equipped with an ASET™ AC, AI or AMI engine, the screen (part no. 25099919) located in
the Y-hose at the oil cooler coolant inlet must be removed and replaced before flushing the cooling system.
Replace Oil Cooler Coolant Inlet Screen — ASET™ AC, AI and AMI Engines

1. Oil Cooler Coolant Inlet Screen (Part No. 25099919)
Note: The Penray 2015 Twin Pac combines the Penray 2010 Cleaner and 2011 Conditioner for heavy-duty
diesel engine cooling system treatment. The 2010 cleaner removes harmful scale and sludge deposits from the
entire cooling system, while the 2011 conditioner flushes the cooling system of loosened deposits, removes any
accumulated oil and conditions the metal surfaces.
Note: If the cooling system is cleaned on a regular basis (for example, when the concentrated coolant is
drained and the system refilled at the recommended coolant drain intervals), or when the system is relatively
free of rust or other deposits, a smaller amount of cleaning solution may be sufficient, or the system can simply
be flushed with clean water.
3. Once the system has been flushed with the commercial cleaner per the package instructions, drain the solution
from the cooling system and refill the system with clean water.
4. After making sure the transmission is in neutral and the parking brakes applied, start and run the engine at
normal operating temperature for approximately 10 to 15 minutes.
5. After running the engine at normal operating temperature for 10–15 minutes, stop the engine and drain the
water from the system. Repeat this flushing procedure until the system is entirely free of impurities.

Note: If the cooling system is severely contaminated, reflush with the Penray cleaner until free of impurities,
and then flush with clean water.

Filling the Cooling System
1. Fill the cooling system with new coolant. Refer to the Maintenance and Lubrication Manual, TS494, for coolant
specifications and cooling system capacities. When filling the system, the engine must not be running and the
heater controls must be set at WARM.
2. Fill with coolant to the maximum level indicated on the surge tank. For chassis equipped with the combination
steel surge tank/plastic recovery bottle, fill until coolant is visible in the sight glass. For MRU, LEU, MR and LE
models, and for chassis equipped with the one-piece aluminum surge tank, fill until the level of coolant is at the
bottom of the fill neck extension inside the tank.
3. Make sure the transmission is in neutral and the parking brakes applied. Start and run the engine until reaching
normal operating temperature.
4. After reaching normal operating temperature, shut off the engine and allow it to cool. Recheck the coolant level
and top off with coolant as necessary.

Issued by
Technical Service