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Simple preventative maintenance tips for a Kenworth engine cooling system and Horton fan clutch.

Kenworth engine cooling systems are built and designed in Australia to meet Australian conditions.

The truck engine cooling system is a critical system within a truck’s operation and has a significant impact on fuel economy, horsepower, emissions, driver comfort and, most importantly, ‘uptime’ – maximising your time on the road.

The cooling system comprises the radiator, water pump, coolant expansion tank, thermostat, engine control unit, control sensors, fan clutch and fan. It serves two purposes: to prevent engine failure due to overheating and to keep the engine running efficiently. Engine cooling is particularly important in Australia with excessive heat, dust and long distances travelled.

To ensure the truck engine cooling system, fan clutch and fan are maintained in optimum condition, scheduled preventative maintenance is critical. PACCAR Parts and Norman G Clark have collaborated to assist with preventative maintenance tips and correct operation of Horton pneumatic fan clutches.  Remember, product designs may vary across different models and installed components should be identified by part number before attempting repair or replacement. Products should only be inspected and replaced by a suitably trained and qualified technician.

Horton pneumatic fan clutches rely on air to operate. Therefore, air integrity and pressure are critical for optimum life and efficiency. It is crucial to check the overall system for air leaks and correct system air pressure. Either of these could result in a reduction in system air pressure, which may cause the clutch to slip and overheat.

Norman G. Clark has manufactured Horton OEM fan clutches in Melbourne since 1980

CHECKING FOR AIR LEAKS

At normal operating pressure, check for leaks at the solenoid valve and Horton fan clutch, across all airlines, fittings and filters, which are a common source of leaks after experiencing concentrated heat and pressure over time.

Air leaks detected in a Horton fan clutch or solenoid valve can be repaired with the appropriate Horton repair kit.

TIP: Firstly, listen for any air leaks and then locate the exact escape point with soapy water while checking for bubbles

CHECKING AIR PRESSURE

A minimum of 90 psi is required for the fan clutch to correctly engage (S & HT/S) and/or disengage (DriveMaster, DMA & DMA-2S) the Horton fan clutch. The air pressure should be checked in two key locations: before the solenoid valve to ensure air system pressure is correct (‘X’) and before the fan clutch to ensure the air solenoid valve (‘V’) is operating correctly, as shown in Figure 1.

Also, check the electrical wiring and plug connections to ensure the correct operation of the air solenoid valve. If 90 psi is not detected at either of these locations, it must be rectified by repair of the air system or replacement of the air solenoid valve.

TIP: The solenoid valve assembly also has a filter assembly on it and should be cleaned and drained routinely to remove any moisture and or contaminants in the air system, as both will affect the life and performance of the system

CHECKING THE HORTON FAN CLUTCH

There are two methods of checking –  visually and functionally.

Visually check the fan clutch for wear and/or any heat discolouration on the piston friction disc (PFD) and friction liner. This would indicate potential slipping and heat generation due to the air system integrity.  The Horton HT/S fan clutch has a System Sentry fuse, located in one of the raised nodes on the PFD assembly.  Should the fan clutch be subjected to excessive slippage causing major overheating, the System  Sentry fuse will melt, releasing the air to the fan drive. This is designed to protect vital fan clutch components from catastrophic failure. In the event of the  System Sentry fuse acting to protect the fan drive, lock-up bolts will need to be installed to allow the vehicle to be driven to an appropriate repair centre.

Functionally check the Horton fan clutch with normal operating pressure and with the ignition on and engine off. Initiate engagement and disengagement of the clutch – both should occur within a second.

Check all system electrical wiring, including the solenoid valve, air-conditioning pressure switch and thermal switch, to ensure correct operation. To functionally check for liner wear, when the fan clutch is engaged and the engine is off, try turning the fan manually and if it can be easily turned this would indicate worn friction facings.

TIP: Horton S and HT/S types also have a small restrictor in the air fitting for  softer engagements, which needs to  be checked as well

 

CHECKING BEARINGS AND ACCESSORIES

Check the front bearing with the fan clutch disengaged. Spin the fan in both directions and check for any roughness.

Check the pulley bearings on the Horton fan clutch. Remove the fan belt and spin the pulley in both directions with the fan clutch engaged and check for any roughness.

Check the bearings in all other cooling system accessories within the belt drive system such as the water pump, idler pullies, alternator and/or A/C compressors.

TIP: Smooth and polished belts and tensioner pullies may indicate belt slippage; therefore, check the belt tensioner’s operation as well.

If there are any defects found in the Horton fan clutch, repair appropriately with either a Horton fan clutch and/or a Horton repair kit. There are different levels of repair kits for different applications, so ask your local PACCAR dealer to determine the best kit suited for your repair.

Finally, visually check the fan and fan shroud for equal and correct clearance around the fan tips and check for any impact marks. Check for axial obstructions before and after the fan with a minimum guide of one inch (2.5cm) to ensure no interference with the fan. Check the fan for any cracks, impact marks, wear and/or damage. If there are any clearance issues, correct accordingly and if there are any defects on the fan, replace it. 

TIP: A clean and clear radiator and bug screen will allow maximum airflow and maximum cooling system efficiency, which will ensure fewer Horton fan engagements, for longer component life and improved fuel savings.

 

PACCAR Parts wishes to thank Norman  G. Clark for its technical advice and contribution to this article.