THE DEFINITIVE TRUCKING SITE

October 2007

Gary Spires demonstrates how to connect an earthing cable

Integral to the efficient working of a diesel engine is its cooling system. Without the correct coolant and antifreeze chemicals in the truck's cooling system, premature cooling system failure could result in costly engine seizure. FleetWatch invited Cummins Filtration's technical experts to shed light on how to better maintain your truck's cooling system.

"The key to coolant protection for high horsepower diesel engines is the correct coolant chemistry," says Gary Spires, Senior Field Service Engineer, Cummins Filtration. "The correct coolant chemistry determines coolant flow rates that do not compromise engine and system component life. High horsepower diesel engines must make use of high coolant flow rates to provide satisfactory engine temperature control over a broad range of ambient operating temperatures."

Protecting aluminium components
Aluminium engine components, used to increase payload potential, can survive demanding operating conditions when the correct coolant formulations and system design parameters are followed, explains Spires. "Coolant pH may have been seen as the cause for aluminium cooling system component damage. However, aluminium coolant system component issues are much more complex. Aluminum component failures are most commonly caused by high coolant flow velocity; flow turbulence and impingement at the aluminum surface; stray electrical currents; diluted, weak coolant due to refilling of low coolant levels with plain water; brazing residues not properly cleaned from heat exchangers; and abrasive contaminants."

Get the balance right
"Industrial Standards as set forth by ASTM (American Society for Testing and Materials) and JIS (Japanese Industrial Standard) allow for coolants to have pH ranging between 7.0 and 11.0," explains Doug Hudgens, Senior Chemical Technical Advisor, Cummins Filtration. "Coolant additive chemistry dictates the allowable pH range. Phosphate/silicate coolants can buffer at pH levels up to 11.0 and still provide solid aluminum protection. Newer organic acid technology (OAT) coolants that do not contain silicate or do contain large amounts of borate buffer (hybrid OAT) cannot exceed a pH of 9.0 without compromising aluminum component protection. Solid aluminum corrosion protection allows for higher coolant flow rates to be well tolerated by engine components. Note that both of the above coolants meet ASTM and JIS standards, yet the coolant with the higher pH provides the better the protection."

Killer currents
Stray electrical currents put aluminum radiators at risk due to the large wetted surface area and thin tube walls, adds Hudgens. "Voltages exceeding 0.100 volts are damaging. Dilution of coolant from water-only refilling results in low levels of metals corrosion inhibitors and reduction of ethylene glycol that inhibits stray currents. Coolants containing antifreeze at levels of 50/50 are more resistant to stray currents than coolants composed chiefly of water. Heat exchangers with brazing flux residues cause corrosion failures at tube-header joints. Abrasives such as core sand and dirt circulating can scour protective films from surfaces leaving aluminum unprotected."

Get earthed 
The advent of aluminium radiators to truck and equipment applications, combined with more electrical components and diesel injection electronic control modules (ECM), the importance of correct earth connections cannot be over-emphasized, explains spires. "Proper earth connections can reduce stray currents to levels with which aluminum components can live. Aluminum radiator failures are the most visible effect of stray electrical currents present in engine coolant."

The harmful electrical current can be caused by insufficient earth connections in the starter, alternator and cab electrical systems, says Spires. "Some systems utilize the steel frame as the major earth return-to-battery circuit. Multiple connections to the frame and corrosion of the earth connections can result in unequal earth potentials relative to the battery (+). Such methods can cause electrical currents from the alternator, starter, ECM, cab electrical, and lighting systems to seek the engine cooling system as an alternate path to the battery (-) earth connection. 

"Field testing of cooling system voltage has been observed to be as high as 0.500+ volts on some systems. Installation of an additional battery cable equal in gauge to the (+) cable between the starter (-) terminal and the battery bank (-) connection plus connecting the cab and alternator earth connections to the starter (-) terminal can result in a significant reduction of the coolant voltage to as low as 0.035 volts or more," continues Spires. "In addition, engine start-up coolant voltage transients of 1+ volt can be eliminated. Frequent engine starting and high alternator electrical loads can result in high voltage transient spikes that greatly accelerate aluminum radiator and component damage."
 

Using factory specified coolant fluids will reduce corrosion and overheating, as well as the winter freeze-up - hello Underberg!

Recommended Procedure to Correct Earth Connection Problems:

• Install an earthling cable between the starter (-) terminal and the battery (-) post

• Create a common bonding point by connecting an earthing cable from the alternator, ECM, electric fans, and cab electrical system to the starter (-) terminal

• Do not install an earth cable to the radiator core. This draws stray currents to the core resulting in accelerated failure

• Clean all earth connections with sand paper or wire brushing. Reassemble connections using conductive grease such as aluminum wiring assembly grease. 

• Spray an insulating varnish on all electrical connections to keep out water and dirt.

Customer maintenance practices that are likely to accelerate aluminium heat exchanger component damage:

• Coolant composed of water-only is more damaging due to dissolved mineral content increasing the electrical conductivity and complete lack of corrosion protection

• Changing coolant filters at long service intervals not approved by the engine manufacturer

• Failure to refill low coolant levels with fully formulated engine coolant

• Not properly reconnecting electrical system earth connections after repairs

• Lack of periodic removal of all earthing connections and cleaning them to bright metal and reassembling using electrically conductive grease such as "NoAlOx" or similar aluminium wiring anti-corrosion lubricant

Recommended Maintenance Practices:

• Follow engine recommendations on cooling system maintenance

• Use antifreeze mixed at 50/50. 

• Change chemical coolant filters at recommended intervals 

• Test coolant SCA (DCA4) levels with coolant test strips to ensure correct maintenance

• Test coolant freeze point to determine if excessive water has been used to refill low coolant levels (-37°C for 50/50)

• Drain watery coolant and refill with new fully formulated coolant.

• Inspect and clean all earthing connections yearly or when batteries are replaced