The Riddle Over rubber
What's going on under the hood? Premature hose and belt failure leave many fleets frustrated.
Deborah Lockridge
Senior Editor
Hoses that should last at least half a million miles wearing out at less than 200,000 miles. Silicone hoses that should last the life of the truck deteriorating from the inside out in just a few years. Belts failing twice within a few months on brand-new trucks.
These are issues being experienced by fleets that seem to be attributable to new technology such as EGR engines, automatic belts tensioners and serpentine belts. If you're not closely monitoring your belts and hoses, maybe you should be.
HOT, HOT, HOT
At the fall meeting of The Technology and Maintenance Council, fleet maintenance managers reported hose and belt problems they attributed to excess heat under the hood.
Darry Stuart works with fleets to improve their maintenance programs through his DWS Fleet Management Services, and he's troubled by the heat-related problems he's seeing in his clients' trucks.
Under the hood temperatures are starting to affect everything from windshield washer bottles to belts and hoses, he says. "We're already seeing hose deterioration at a very young life," Stuart says. "My expectation is that hoses should last a minimum of 500,000 miles[and] we're seeing hose degradation at under 200,000 miles."
Heat takes its toll on other components, as well, from wires to fan clutches to alternators and power steering pumps. At least one alternator manufacturer has reportedly made some design changes to compensate. But how heat is affecting other components may not be as obvious as belts and hoses, Stuart says. "If a belt goes because of heat, we instantly know there's an issue. If a radiator hose fails, it's an instant issue."
Many believe the culprit are the new low-emissions engines, introduced in 2002, that use exhaust gas recirculation to control emissions.
"With the added requirement of EGR, we end up with a lot more hardware under the hood than we had before - and it's all hardware that gets hot," says Rod Ward, director of sales engineering at silicone hose maker FlexFab. "It's all generating heat under the hood, and it's also restricting the air flow coming through the radiator. So we're seeing heat build up in certain "dead spots,' and that's what's causing the added heat strain on coolant hoses, on fuel hoses, and also on the turbocharger hoses."
Ward notes that the hottest location is the side of the engine where the EGR cooler is located. "Before, you just had the exhaust manifold," he says. "Now you have the manifold and the EGR cooler system. It's mostly due to EGR piping and more exhaust gases having to be cooled. Before, you just ran out the exhaust tailpipe and got rid of that heat. Now that heat is brought back to the front of the engine compartment, and all those BTUs of heat have to be transferred back from the water into the air."
It does not appear to be an across-the-board issue. We talked to plenty of fleets running EGR engines who have experienced no problems at all.
"Really, [the temperature change] was just a slight bump, about 5 to 10 degrees," says Everett Bowen, project manager with Gates Rubber. "We did a lot of investigation prior to the actual introduction of the engines, because we were wanting to be sure that the products we were marketing and selling were going to continue to perform under those new conditions. The company has not had complaints from customers regarding any premature belt and hose failure due to excess heat," he says.
Bill Stahl, director of OEM service at Cummins, was at the TMC meeting where the complaints were addressed recently.
"We do not recognize an under-the-hood air temperature issue that exceeds the ability of the materials' capability to live," he says. "I was on the Cummins audit team when we looked to release the EGR '02 engine, and my responsibility was under-the-hood temperature."
In that capacity, Stahl looked at questions such as whether heat shielding was needed, and says the team did not anticipate any sort of underhood air temperature issues.
"It is not an across-the-board EGR issue, period."
Peterbilt was probably the most vocal of the truck manufacturers in its concern about possible heat issues before the "02 engines came out. As a result, the truck maker has kept an eye and ear out for any possible problems - and has not seen any.
"We did extensive testing before launching the new engines and have been very cognizant of that as trucks have been in the field," says spokesman Derek Smith. "The ambient temperature under the hood has not gone up that much, but our engineers did keep that in mind when it came to routing hoses and that sort of thing around the engine."
Many of the fleets reporting problems are running Mack trucks, and Mack has been working on the issue.
"We have been very proactive in dealing with this issue," says Bill Smith, Mack reliability engineering manager, while noting that all EGR engines, regardless of manufacturer, produce more heat under the hood. "We've initiated a number of product improvement campaigns, which give customers the opportunity to bring their trucks in for enhancements at our expense."
Mack has replaced the original neoprene drive belts with more heat-resistant polyethylene belts. It also has added thermal heat sleeve material on the fuel return line. Plastic air governor lines have been replaced with stainless steel braided hoses that have Teflon inner liners. The company has added more heat-resistant main drive belt tensioners and alternators, and a windshield washer reservoir heat shield.
"We've incorporated all of these improvements into new vehicles coming out of our production plants as well," Smith says. "And we will continue to work closely with our customers to address any and all issues until they are fully resolved."
Mack also recently introduced its new Advantage highway chassis, which features a wider front frame section, allowing for a 10% larger cooling system.
While many of the reported problems appear to stem from EGR engines, one fleet we spoke with starting having heat problems before the low-emission engines even hit the streets.
Truck-It, a 25-unit truckload fleet based in Kentucky, has silicone hoses deteriorating from the inside out, as well as abnormal belt failure - both appearing to be heat-related - on 2000 model Freightliner FLDs with Cat power.
Director of Maintenance Roy Gambrell is perplexed and frustrated. "All I can tell you is I got silicone hoses failing that I normally would not replace during the life of the truck, and I'm seeing them fail in 24 to 30 months. Belts and alternators also seem to be failing prematurely," he said.
Gates Rubber's Bowen raised the possibility that some fleets could be mistaking heat aging for heat-related failures. As the rubber in the belts and hoses is exposed to heat over extended periods of time (what's know as heat history), the material will start to harden, he explains. It gets to the point where a vibration in the system will actually start to crack the material because it has no more flexibility left. It will progress to a rupture or a blowout in the hose itself.
However, Bowen says, what a lot of people perceive as heat failures is actually what we call electrochemical degradation. This happens because the different kinds of metals used in the cooling system - brass, aluminum, steel, cooper - set up an electrical charge in the system. The coolant/antifreeze carries this charge through the engine block and cooling system, and the charge will actually attack the carbon bonds in the rubber. This will cause small striations, or cracks. Over time, these cracks will grow and eventually will cause the hose to lose its integrity and rupture. Electrochemical degradation can cause a hose to fail in two to three years, he says.
While the appearance of cracks and rupture may look similar with both types of failure, Bowen says, you can pretty easily tell the difference. In one case, the hose is hard - it's gotten hard because of the heat. In the other case (with electrochemical degradation), the hose is still soft.
BELTS & TENSIONERS
Heat is also suspect in reports of shorter belt life, but some problems seem to be inherent in the design of today's engines. Engine designers are increasingly using an auto-tensioning, flat-ribbed serpentine belt (similar to what is used in automobiles) rather than the traditional multiple V-belts.
David Warren, Kenworth product marketing manager, expects to see more engines equipped with serpentine belt-drive systems. According to Warren, these systems provide a more compact design that allows engineers to optimize the fan drive system needed to manage the high heat rejection from lower-emission engines.
Mack has been using flat-ribbed serpentine belts for some time, and they are also on the new ASET '02 engines. Manual belt adjustment is not needed with the automatic belt tensioners used, note Mack engineers. However, they admit belt replacement is more difficult because of the tight clearances around the new fan ring components. The trade-off, they say, is by keeping the belts at optimum tension, the automatic tensioners mean longer belt life.
Yet many fleets are reporting problems with the serpentine belts, also called poly-groove, micro-V or poly-V belts.
All of a sudden, the life of those things are a third of what V-belts were, Stuart says.
Unlike a traditional V-belt, which typically only goes around two points (such as the camshaft and the component it's driving), the serpentine belt goes around multiple pulleys, with the typical poly V belt driving four or five components, says Gates' Bowen. Every time it goes around that pulley, it has to flex, and that flexing and straightening over time is what causes it to crack. So by it's nature its not going to have the life of a single V belt.
Stephen Sabo, maintenance manager at Norrenberns Truck Service in Nashville, Ill., is seeing a lot of premature automatic tensioner failures, and says the belts don't seem to last as long.
"On the good side, they have done their job extremely well in a lot of applications," he says. "You don't have to adjust the tension, so that saves man hours. But sometimes they come apart and the truck is down. Since there is next to zero maintenance on automatic tensioners, predictability of failure is not good."
As with hoses, some fleet suspect excess heat from EGR engines may be partly to blame for belt problems.
Ron Szapacs, maintenance specialist at the private fleet of Air Products and Chemicals, has been having serious problems with belts on his 2005 model Macks that were put into service last summer.
"We've had locations where we have had 100% of the EGR units with belt failures," Szapacs says. "At the same locations we've had 30% to 35% of second time failures. These trucks all had no more than around 50,000 miles on them. He has been working with Mack and made all the changes recommended, including a new type of belt and new tensioners, but he is still seeing premature failures. He has talked to several other fleets experiencing similar issues.
"We haven't had this problem with pre-EGR units," he notes.
WHAT TO DO?
The first step is to inspect belts and hoses closely and frequently.
"The belt and hose [life] expectation is from PM to PM, as far as I'm concerned," Stuart says. "If you're properly inspecting the vehicle, checking belt tension and pressurizing the radiator, there's a good chance that you will see [signs of impending failure] at PM time."
Checking belts and hoses regularly is your best bet against roadside breakdowns, says Harvey Bieber, product manager for replacement products at Goodyear Rubber. "It's a fairly simple process to go around and do some hose squeezing, to flip the belt over and see if it has cracks or chunks falling out of it, and change them regularly."
For belts, maintaining the proper tension is vital. Goodyear engineers like to say that tension is as important to belts as air pressure is to tires. While automatic tensioners are fairly maintenance-free, Bieber says, they still need some attention.
"The thing you want to look for is noticing on the tension side whether it's flopping around a lot, or if you hear a clacking noise, there may be a problem with the spring in the tensioner."
Bieber recommends inspecting the automatic tensioner whenever the belt is changed. The bearings should roll free, with no rumbles and no resistance when you check them, he says. A more conservative recommendation is to change the tensioner whenever you change the belt.
If you're experiencing premature failures that seem to be caused by heat, FlexFab's Ward suggests shielding or jacketing the affected areas when possible. "There are a lot of different products," he says. "There are some foil-coated products you can snap over the hoses, or there's some nylon shielding that is convoluted and creates trapped air to act as an insulation barrier."
Stuart says he's even considering the extreme step of cutting scoops into the hoods of trucks to bring in more outside air flow.
Make sure you're using high-quality belts and hoses. Gates' Bowen notes that lower-grade EPDM hoses can have a lower resistance to heat as well as electrochemical degradation.
"One thing we've seen in the past couple of years is a real strong push into the U.S. market in coolant hoses from offshore, places like India, Thailand, Eastern Europe," he says. "We know for a fact that some of these hoses coming in don't have the ECD resistance requirements or characteristics."
Look for products that are designed to run cooler. Goodyear, for instance, says its Gatorback poly-V belts have a cog pattern that cuts across the grooves, rather than the typical ribbed-style belt. Typically in belts, the wear is caused by the flexing of the belt going around the pulley, Bieber says. Since it's cogged, it develops less heat, and tests show it performs longer than a straight ribbed-style belt.
Discourage drivers from shutting down the truck immediately after coming off the road. The rubber of belts and hoses soaks up the most heat after you shut the engine down because there is no air flow to dissipate the heat.
"We're talking about an exhaust manifold that heats up to 600 to 1,000 degrees, then you've got coolant temperature components at about 230 degrees," Bieber says. "As long as the engine is running, the fan's moving air through the engine compartment and over the radiator, that's fine. But when you shut it off, all that heat just sits under the hood and cooks everything until it finally cools down."
Some predict that you may see a trend of fleets going back to spec'ing silicon hoses, which can take higher heats.
"At the TMC meeting in Nashville in the fall, a lot of fleets came to us and said, "We're starting to order your silicone hose again,' " says FlexFab's Ward. "They are starting to go back to the silicone option because they're starting to see premature failures and premature aging of hoses."
When silicone coolant hoses arrived on the market in the '70s, they were the darling of the industry because of their long life. Over the past five years or so, though, there has been a trend toward less expensive hoses made of a synthetic rubber called EPDM (ethylene propylene diene monomer). That's partly because the performance of EPDM has improved to where it is comparable to silicone in terms of performance, with premium EPDM hoses running half a million miles or more. International, for instance, now uses a premium EPDM hose that can handle service temperatures up to 300 degrees.
Proponents of silicone hoses say they last longer than traditional rubber hoses. Silicone coolant hoses are standard on Kenworth T2000 model and are a popular factory option on other Kenworth trucks, says Kenworth's Warren. Silicone hoses help resist weathering, ozone, heat and coolant deterioration, he says.
However, some fleets that are reporting failures are seeing them in silicone hoses, so it's not entirely clear that's the answer.
In fact, there seem to be more questions than answers when it comes to shortened belt and hose life. Your best bet? Don't overlook belt and hose maintenance.
You may need to revamp your hose and belt preventive maintenance and inspection procedures to avoid costly breakdowns and downtime on the road.
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