COOLING SYSTEMS’ SNEAKY CORROSION
Cooling failing to maintain an antifreeze/additive package is an invitation to cooling system corrosion. But, according to a panel of experts at the fall meeting of the Technology & Maintenance Council, the causes of accelerated corrosion due to electrolysis are not widely understood.
Stray electrical current can travel through cooling systems and wreak havoc, according to Jerry Woerner, manager for service and warranty at Behr America. The problem, Woerner says, is often a case of poor vehicle grounds forcing current to seek alternate ground paths. This can remove metal from cooling system surfaces, causing pitting, corrosion and, ultimately, leakage.
Darrell Hicks, OEM manager for Penray, recalled an owner-operator who would carry spare water pump backing plates in his cab because they would corrode and leak so quickly. The problem, he said, turned out to be a bad ground.
A lesser form of electrolysis, can occur naturally in cooling systems by way of the electrical potential between dissimilar metals. If you’ve ever inserted a nickel and a penny into opposite ends of a citrus fruit, and measured voltage across the two coins, you have made a crude battery. Some cooling systems can produce the same result.
So how do you protect your equipment? Roger Sells, field service engineer for Fleetguard/Nelson, suggests starting with the basics: Fill cooling systems with pure water, a low-silicate antifreeze mixed to the proper dilution – usually 50/50 – and the recommended dosage of a supplemental coolant additive (SCA). Top off only with a fully-formulated antifreeze or one that meets TMC’s Recommended Practices 329 or 330 specifications. Use a test strip to check for the proper SCA level twice a year.
Finally, Sells advises, occasionally observe the color, odor and clarity of your vehicles’ antifreeze. If something seems wrong, it probably is.
To check for stray cooling system current, Behr’s Woerner suggested attaching the negative lead of a digital volt/ohmmeter to a vehicle’s negative battery terminal, and immersing the positive lead (preferably with a platinum test probe) into the vehicle’s coolant, taking care not to touch any metal. The measured voltage should ideally be 0. If voltage is 0.1 or higher, he said, there is stray current in the system.
Mike Jeffress, vice president of maintenance for Maverick Transportation, reported on testing on several of his fleet’s vehicles, where voltages ranged from 0.3 to 0.7. He recommends inspecting vehicle grounds and seek help from suppliers.
While there was some discussion as to how prevalent and harmful natural cooling system electrolysis is, all agreed that stray voltage from poor grounds can exacerbate an already undesirable condition.
DIFFERENTIAL LOCK OPERATION EXPLAINED
ArvinMeritor’s Commercial Vehicle Systems group is offering a multimedia information kit, featuring operation instructions for an optional driver-controlled differential lock (DCDL) and the standard inter-axle differential (IAD) lock for Meritor drive axles.
The information is designed to educate heavy-duty truck operators and technicians on the benefits and operation of the two devices, and provide information on an optional pump and filter system.
A DCDL provides maximum vehicle traction and control on unfavorable road surfaces. An IAD is a driver-controlled, air-actuated traction device that allows for speed differences between the forward and rear tandem axles, while providing equal pulling power from each axle of the tandem.
The kit may be ordered complete or by individual items at www.arvinmeritor.com/
tech_library or (800) 535-5560.
A TALE OF TWO PISTONS
Although it might look it, the piston on the left wasn’t beaten with a hammer. But it was featured in TMC’s Failure Analysis Roadshow this fall. According to Bill Stahl, Cummins’
director, OEM service, this is the result of a diesel engine operating on gasoline or a gasoline/diesel mix. The gasoline is quick to detonate prematurely and, combined with a diesel’s high compression ratio, explodes violently enough to permanently damage pistons.
The piston on the right, says Stahl, was the victim of severely over-advanced injection timing. With ignition beginning far too early, the resulting explosion cannot push the piston down, and burns in the crevice volume, above the top ring, removing metal as it does so.
Look for more failure analysis clues and answers in upcoming issues of CCJ.
EMISSIONS TECHNOLOGY RACE INTENSIFIES
Two heavy-duty diesel engine makers that are major suppliers in both North America and Europe have begun working to ensure that the European solution to the next round of engine emissions cuts will also work here. Volvo Powertrain, which builds engines for Volvo and Mack, and DaimlerChrysler’s Detroit Diesel Corp. want to use selective catalytic reduction (SCR) technology on both sides of the Atlantic so that they don’t have to invest millions in developing two separate solutions.
As we reported in July, two divergent emissions-control technologies are under consideration for use in 2007, when tighter diesel exhaust emissions regulations take effect.
One leading contender combines cooled exhaust gas recirculation – or Caterpillar’s ACERT – with particulate matter (PM) traps and nitrogen oxide (NOx) adsorbers. A PM trap, which resembles a muffler, extracts exhaust soot via a ceramic or metallic filter that’s continuously or periodically purged and regenerated. A NOx adsorber collects the pollutant on the outside of its internal element (as opposed to an absorber), then the system goes through a rich-fuel cycle to convert it to less harmful substances.
The other likely candidate is SCR, which uses ammonia provided by introducing a urea/water mixture from a vehicle-mounted tank into the exhaust, upstream of a catalyst.
Already used in Europe, SCR systems reportedly can reduce NOx, while allowing for an engine calibration with better fuel economy. However, there are concerns, such as the need for additional vehicle tanks and an infrastructure for obtaining urea.
Moreover, the Environmental Protection Agency, while asserting its neutrality on which technology is ultimately used, has expressed concern that SCR could place the onus of emissions compliance on vehicle operators, since they will need to ensure that their vehicles have an an adequate supply of urea on board.
To help develop a better understanding of the key components of a new urea supply chain, and to brainstorm various scenarios for a distribution process sufficient to support SCR technology, Volvo Powertrain and Detroit Diesel Corp. recently hosted the first meeting of the Urea Distribution Stakeholder Group, comprising 25 representatives of urea producers, chemical distributors, truck stop operators, fuel refiner/distributors, fleet operators and SCR component and truck manufacturers. The open meeting explored the means for developing an integrated urea distribution proposal for discussion with the EPA.
