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Maintenance Q&A
Exhaust woes and the impact of ULSD

By Paul Abelson
Senior Technical Editor

Q: I've been waking up with headaches after sleeping in my truck. I don't have a generator or any of that fancy stuff so I have to idle my truck. I don't stop where I can't idle. A friend said I may have exhaust gas in my truck, but the shop checked it and said there wasn't anything wrong with my exhaust.

A: This sounds similar to a problem a driver for a major truckload fleet had.  It almost cost her her life. While the exhaust system starts at the engine, the stacks and some mufflers are often cab-mounted.

Because they move differently, pipes must flex. Exhaust is too hot for rubber or polymers to handle the vibration, so trucks have spiral or circular bands that lock together with an interference fit. This flexible tubing brings exhaust around corners and allows parts of the system to vibrate at differing rates.

Stones can slightly dent the rings, causing pinhole leaks. Road salts can corrode the tube, causing leaks. The driver I mentioned had a leak that was difficult to detect. She complained so many times that the shop stopped paying attention to her. Things got so bad that she had to see a doctor, who told her she was weeks, if not days, from having permanent heart damage from carbon monoxide poisoning. She had to recuperate for more than six months.

Buses carrying passengers do not use flex tube. They rely on bellows-like seamless stainless steel tubing. Microflex Inc. is one of the bus industry's leading suppliers. The bellows tubing will not leak the way flex pipe can. However, bus and truck vibrations differ, so you should consult with a dealer before ordering parts. You might want to change to rigid stainless elbows between sections of bellows tubing.

Q: What are the effects of the new ultra low-sulfur diesel going to be? I hear that lubricity may be an issue. Should I be stocking up on additives now? Or, will the new fuel contain enough additives to make up the difference? (Another reader wrote with similar concerns: Will there be any issues with pre-EPA motors - 2003 and older - when the new ultra low-sulfur fuels are brought out in '06?)

A: I've been told that the new, 15-ppm sulfur, ultra low-sulfur diesel has just a bit less energy content - fewer Btu - than today's 500-ppm sulfur fuel. Other than that, there should be no differences, and the lower Btu content may not even be noticeable. It may reduce fuel economy by only 0.01 to 0.02 mpg. However, since Btu content varies according to the crude that is refined, you may not be losing anything in the switch and you may even gain fuel economy.

Lubricity will be reduced because sulfur is a good lubricant, but additives will be in the fuel to restore the little that is lost. It isn't like when we went from 3,000-to-5,000 ppm down to 500-ppm sulfur. Biodiesel may come into its own as a lubricity improver in addition to being a renewable fuel.

ULSD will start being delivered this summer to purge tanks of low-sulfur diesel in advance of the start date. In October, the phase-in becomes official. At that time, 20 percent of the output of smaller refineries can still be low-sulfur diesel, but the phase in must be complete by 2010. If you have an older engine, it could pay to look for older and cheaper diesel until it's all gone.

Q: I have a '99 Pete 379 with a Cat 3406E 600-hp. Everything was fine for the first five years, but then the Horton fan clutch started slipping. Then it wouldn't come on. I had it replaced. It happened again and again, each time more quickly. Now I'm on my fifth clutch in little more than two years. With summer coming, I'm afraid of the engine overheating. I checked and there aren't any recalls on the fan clutch. What can I do?

A: There are two kinds of air-activated fan clutches. Some use air to activate the fan. If an air line breaks, they revert to a fuel-saving fan-off condition.

Others use air to disengage the fan, defaulting to a horsepower-consuming, always-on condition that consumes excessive fuel.

Either way, the symptoms sound like your fan clutch isn't getting enough air to properly activate. The more frequent failures indicate an increasing blockage of air to the clutch.

Paccar trucks have a small filter for air to the fan clutch, mounted on the firewall. Trace the air line back and you'll find it. The filter is often overlooked during routine maintenance, especially by younger, less experienced technicians. I'd bet yours hasn't been changed for at least the two years you've been burning out clutches.

Q: The door locks on my 2003 Freightliner Century are sticking. Every fall, I lube the locks as part of winterizing. Usually they work fine. This year, they acted like I used molasses instead of lock oil. Finally, the passenger side just froze. I used a lock de-icer and got them working again, but they're still stiff. What can I do?

A: I checked with a local locksmith for this one. Many products for locks contain graphite. Some suspend the graphite in oil; others are straight, dry graphite. The oil-graphite mixtures become paste-like and can eventually turn solid. Straight graphite will not do this, and should be good to use.

Locks contain dissimilar metals, brass, aluminum and steel. Vapors from today's corrosive snow-fighting chemicals get into locks and corrode them.

Locks should be lubricated when you winterize and summerize. Use enough de-icer to dissolve the graphite-oil residue. It may take a number of applications.

De-icer will leave the locks unprotected. So, you'll need to protect the locks. The locksmith recommended Tri-Flow, a very light petroleum-based penetrant and protectant that contains Teflon. It displaces and repels water, and the Teflon will keep things operating smoothly. Don't be afraid to overuse it. It's thin enough to drain through weep holes and won't hurt anything it contacts.

Q: My hoses are starting to go on my 2002 pre-EGR Detroit. I've been told to use silicone hoses, but they are very expensive. Are they worth it?

A: Silicone hoses are more heat-resistant than conventional rubber, but they are susceptible to abrasive wear. Keep them from chafing and they will last a long time, possibly the life of the truck.

When installing, silicone hoses tend to extrude through slotted worm-type clamps. Special clamps that are better for these and all hoses have a solid band under the slots for the worm drive.

The best are the temperature-compensating, constant-torque clamps. They have a spring at the tightening screw. The spring moves the adjustment mechanism in and out as hose fittings heat and cool. Torque remains constant as fittings expand and contract. Adjustment stays constant.

These clamps cost a few more bucks than lesser clamps, but they are reusable and prevent leaks and hose damage. If you're spending extra for silicone hoses, you might as well go all the way to protect your investment.

Paul Abelson may be reached at