Truth in numbers

| June 01, 2006

Knowing how to read instrument panels can increase safety and decrease breakdowns.

A big truck’s dashboard gauges can’t predict the NASCAR points winner or even the Apocalypse.

Still, professional truckers cannot safely and effectively do their jobs without the information their dashboard gauges show them.

“Your instrument panel gauges will give you a fundamental idea of what’s going on with your truck,” says owner-operator John Gray from Memphis, Tenn.

Understanding and applying gauge data is part of a professional driver’s job description, just like backing up or logging drive time. Without gauge data, you cannot safely operate the truck. At best, ignorance about gauges will stop the truck. Worse, it might destroy an engine, a drive train or the entire vehicle. Worst of all, if you choose to remain ignorant about gauge data, or if you just don’t read gauges, you might be a danger to yourself and others on the road.

But you’re a driver, not a mechanic. Why should you know the engine’s revolutions per minute or optimum coolant temperature? What do you care about engine oil pressure or if the needle on your primary air tank’s pressure gauge keeps rising and falling, even when you’re sitting still?

Some drivers feel this way. After all, they don’t own the trucks. This is a problem. As strong and rugged as big-truck diesels are, they can be ruined easily by drivers who don’t understand them, and too many drivers don’t.

As if to emphasize this, most original engine manufacturers now design their products to shut down automatically if they’re being run without sufficient coolant or oil. In other words, the OEMs anticipate that truck drivers will not bother themselves with the trivia from engine oil and temperature gauges.

The automatic shut-offs annoy drivers. But they can save the truck’s owner $20,000 for a new engine, and if drivers take better care of the engines, such baby-sitting devices would not be necessary.

“If a driver doesn’t understand the oil pressure gauge, he can lose the engine,” says D & R Trucking company driver Bill Lawrence from Martinsville, Va.

When an engine goes down, somebody has to pay a lot for it, and freight does not get delivered on time.

“Diesel engines are not like car engines,” says Lawrence, who has more than 40 years of experience. “A car engine’s compression is usually about nine or 10 to one. In a diesel, it’s more like about 250 to one.”

The higher compression drastically increases the need for adequate lubrication inside the engine. “Diesel fuel has additives in it that give it some lubricating ability,” Lawrence says. “But if you lose oil pressure, that engine will seize up quick.”

That’s why mechanics say that more than any other factor, an adequate flow of oil to the engine, or the lack of it, will determine the engine’s life and performance.

“Running down the highway, I’m right at about 55 pounds of oil pressure,” says owner-operator Gray, who has a 3406E Caterpillar engine. “If the oil pressure drops much below that, I know something excruciatingly wrong has either happened or is about to happen.”

Like most newer engines, Gray’s 3406E has sensors that shut it down if its oil pressure drops. “If the oil pressure or water temperature go bad, then the engine will go into automatic shut-off mode,” Gray says. “It usually lasts about 10 seconds: long enough to get the truck off the road.” Then the engine shuts itself down. To protect itself from abusive drivers, it won’t start again until the problem is solved.

Correct operating and idling oil pressure varies according to the engine. Gray’s CAT is happy with 55 psi of oil pressure, but Lawrence’s Detroit Diesel Series 60 likes it between 40 and 50 psi.

“If it gets below 40 psi, I’m either low on oil or about to lose an oil pump,” Lawrence says.

But big truck engines aren’t always at highway speeds, and an engine low on oil is more likely to get inadequate lubrication when idling. “It should stay at about 30 psi at an idle,” says Lawrence of his Series 60.

Faithful to the last, big diesels without automatic shutdowns will keep idling and slowly destroy themselves if they don’t get enough oil. So drivers should know what a good idling oil pressure level is, too.

Finding out isn’t hard.

“Look in the owner’s manual,” Lawrence says. “It will show you every gauge on the instrument panel and tell you what it’s for and what it should read. They also have an 800 number to call if you have questions.”

For some, a trusted mechanic is a better source. “If one of my gauges isn’t reading what it should and I don’t know what to do about it, I’ll call my local CAT representative,” Gray says. “We go through a list of possible scenarios. He can tell me if the truck is safe to drive or if I need to have it towed in.”

If owner’s manual and trusted mechanic aren’t available, contact your employer’s maintenance, road service and/or safety departments.

Truck drivers necessarily believe they know everything. If they don’t know, some will make up something that sounds true instead of just asking. Some questions, such as, “What should the oil pressure be at idle?” are hard to ask, but they’re not nearly so hard as telling your employer he has to spend $20,000 for a new engine because you ignored or didn’t understand the oil pressure gauge’s reading.

Besides, trucking company owners smile when their drivers take care of the company’s costly tools, so asking that seemingly dumb question will probably make points with your boss.

For example, what temperature is too hot for engine coolant? At idle? Running down the highway?

“Mine runs at about 175 degrees,” Gray says. “That’s about normal for my engine, but it varies from engine to engine.”

Find out from the owner’s manual, the engine maker or your employer’s maintenance department what your engine’s coolant temperature should be, and keep an eye on that gauge.

Two more important gauges are those that measure pressure in the truck’s primary and secondary air tanks. Big truck suspensions, seats and, in some cases, starters all run on compressed air. But so do the truck’s brakes, and this is where a lack of knowledge about gauges can result in serious injury or death.

“My air pressure gauges read about 120,” Gray says. “If they start to fall below that, then I know something isn’t right. Either the governor that tells the compressor to pump to 120 psi is bad, or maybe the compressor is bad.

“Normally a leaky air line won’t lose enough air so the pressure falls too low unless the line is broken completely in half, and then you can get a connector and put it back together.”

The air pressure gauges tell you if you can stop the truck. Check them continually. If the needle drops down and comes back up continually while the truck is running, or if it drops down and does not come back up, have the system checked and repaired before you take the truck on the road.

Another important gauge is the tachometer, which tells how fast the engine is turning: information mostly applied to shifting gears.

Experienced drivers often know when to shift without using the tach. “I started out with an old Mack B61 back in 1965,” Lawrence says. “The tach had numbers, but we’d listen to the sound of the engine to know when to shift.”

Drivers who have yet to develop this technique should shift with the tach. Under normal conditions, shift at about 1,500 rpm. For smoother, grind-free downshifting, check the engine rpm. Pull the transmission out of the higher gear, then rev the engine to at least the same rpm before dropping into the lower gear.

The tach can also increase fuel mileage. Shifting and cruising at lower rpm uses less fuel. But engine make, road conditions, weight and gearing will all factor into the best cruising rpm, so ask your employer at what rpm the truck should be run.

Another gauge that gives crucial information is the voltmeter. It tells how much electricity the truck’s alternator is making. It should read at least 13.5 volts.

“A lot of drivers don’t know this,” Lawrence says. “If your alternator’s not producing 13.5 volts, then you’re not putting enough power back into the battery, and you’ll eventually get to where your truck won’t start,” he says. “You need at least 13.5 volts to keep ahead of the draw on the batteries.”

These five gauges – oil pressure, engine coolant temperature, air pressure, tachometer and voltmeter – will be found in almost all trucks, and in all trucks the information they provide can be the difference between late and on-time, rolling or stranded, high or low repair bills, and even life or death. It’s part of a professional truck driver’s job description to understand and use information the gauges provide.
