Hot enough for ya?

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We all knew that lower-emitting, post-October ’02 engines were going to run hotter than their predecessors. And, despite beefed-up cooling systems, we’ve seen things like premature hose cracking and evaporating windshield-washer fluid. I’ve even heard scattered reports of the fluid boiling in its reservoir.

What couldn’t have been known in the early stages is that there are longer-term effects of elevated underhood temperatures that are just starting to show up. That was one of the topics discussed at a technical session at last month’s meeting of the Technology & Maintenance Council, and some of the findings may surprise you.

For example, the fan in Photo 1 displays fatigue cracking at the blade tips. Since the tips flex the most, fleet executives learned, some gradual fatigue is expected. However, high heat allows them to flex further, and premature cracking is the result. The conclusion? Fan inspection now should be considered a part of every PM.

The belt tensioner pulley in Photo 2 appears to have seized its bearing and locked up while the belt continued to turn. But on an 85,000-mile engine? Why?

Pulleys like this one are greased and sealed permanently. However, with constant exposure to higher heat, grease degrades into its component oils and thickeners. The oil eventually weeps past the seal, leaving the bearing unprotected. With the resulting increased friction, even more heat is generated, and the bearing seizes.

What to do? Fleet executives are advised to check tensioner pulleys at PM time. With the belt removed, the pulley should turn with a slight amount of resistance, indicating that the grease is still in place and doing its job. If it spins completely freely, the grease is on its way out, and it’s probably time to replace the unit before an on-road failure. And if there’s a lot of resistance, the grease is gone – and so is the pulley.

Even electrical components aren’t immune to higher-heat environments. Insulation on A/C high-pressure switch wires can become limp from heat, removing some support and allowing the wires inside to flex further than normal due to engine and road vibration. Ultimately, vibration failure could be initiated by higher heat than the assembly can handle. The fix, in this case, would be to secure the harness closer to the switch.

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A helpful tip offered by Kenworth district service manager Tom Tahaney: When a wire breaks, remove some insulation and look at the color of the wire itself. If it’s green, there’s a moisture problem; if it’s shiny, vibration is the culprit; if it’s dark, heat was involved.

But how to prevent these and other premature failures? “Ultimately, some components – like that pulley – aren’t being built to withstand their operating environments,” says Darry Stuart, president of Quickway Transportation, who chatted with me after the meeting. “It may be that we need to stop squeezing our suppliers and get used to paying more for components that will last.”