Cover Story
Tuning up
Even tried-and-true equipment needs special attention to make sure it's ready to perform in the clutch

By Jeff Barker, contributing writer

Some players won’t give up on their trusty equipment no matter what. And that’s OK, as long as it’s up for the pressure of performing when you really need it.

A growing number of engine-based auxiliary power units have been on trucks for several years now and may need attention, especially inside “the box.”

If it hasn’t happened yet, chances are it will. You will park at the end of a long workday on the road. Then when it’s time to retreat to the sleeper, you will fire up your APU and crawl into bed.

During the night, you will wake up to what could sound like the painfully loud noise of an old lawn mower with a muffler that rusted away years ago running at full throttle. Once you’re awake and wondering where the annoying racket is coming from, you eventually realize that it is the APU on your truck.

It’s common knowledge that drive belts and other items need to replaced, and they need the oil and filters changed after so many hours. However, many people forget about the exhaust systems and generally feel that “if it isn’t broke, don’t fix it.” Unfortunately, that frame of mind can result in some very costly repairs down the road.

Before you ever do any kind of maintenance or repair on an APU, make sure the negative battery cable to it is disconnected to prevent a possible accidental startup from taking place. Also, make sure the cab and sleeper are locked and unoccupied with the keys in your pocket so that no one else can start the truck’s main engine and move it.

First things first: Check for an exhaust leak.

One easy way to tell that there’s an exhaust leak inside an APU’s housing is if you see blue smoke coming from the exhaust system. This will happen if the air filter becomes clogged with soot.

This will cause the engine to draw oil into the intake manifold through the crankcase ventilation system and burn it. If this goes on too long, the engine oil level could drop and cause possible engine damage, especially if the low oil shutdown circuit (if equipped) fails to work for some reason.

If you see blue smoke from the exhaust, shut down the APU immediately and check the air filter. If it’s clogged with soot, there’s likely an exhaust leak inside the housing that needs to be repaired before the APU can be operated again.

Whenever any scheduled preventive maintenance is done on an APU and at any other time its covers are removed, take a few short minutes to look closely at the exhaust system. Any black soot formation is a definite sign of an exhaust leak that needs to be properly repaired.

You will be able to see the exhaust manifold mounted to the engine’s cylinder head. Make sure it’s not cracked, no gaskets are leaking, and no bolts are loose.

A section of flex pipe likely is attached to it and may be wrapped in insulation. Check the clamp at the manifold as well as the other clamp where the flex pipe attaches to the exhaust system and be sure they’re tight.

Make sure there are no signs of breakage in the flex pipe itself, which can also be identified by soot formation. If the insulation around the flex pipe is torn or missing, it should be replaced. The insulation keeps the excessive exhaust heat from damaging nearby electrical wiring harnesses and other components.

If an APU is running louder than usual, it’s probably because of a broken flex pipe or other piping in the exhaust system between the engine and the muffler. If the break is within the housing, it could clog up an otherwise clean air filter within just a few hours of operation and create a lot of resonant noise. If it’s outside of the housing, it will be even louder and you will probably get a lot of dirty looks from annoyed drivers who are parked nearby.

If the original exhaust system on your APU has seen better days and is in need of replacement, you should be able to replace it with a quieter aftermarket muffler and reroute it to exit just ahead of your drive axles. The side exit exhaust system that comes on most APUs could pose a safety hazard if diesel exhaust accumulates under the sleepers of trucks in adjacent parking spots.

Side exit exhaust systems on APUs, along with a growing number of trucks with “crop burner” (ground exit) exhaust systems, are major reasons why drivers should invest in a good quality carbon monoxide detector. It could amount to a $50 investment, but that’s cheap if it alerts you to move your truck away from deadly fumes. LL