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Introduction

I have seen many articles and heard many owners of diesel powered pickups complaining about various problems they have had...usually with transmissions, from pulling large trailers in mountainous terrain. We all see semi’s in the mountains on every trip, but what we do not often see is one of them smoking terminally at the side of the road. Why is this? They are routinely pulling massive loads on the same grades that give RV’ers heartburn, so what is different between our rigs and theirs?

Not much really, other than that the machinery involved is proportionately heavier in order to safely carry the loads. Fortunately for us, it is relatively simple to equip a diesel pickup so that it will comfortably haul loads at the Gross Combined Weight Rating (GCWR) for which it was designed. The more difficult task involves educating the driver as to how this equipment will work at its best.

A tour through the average highway tractor’s “office” would reveal a few gauges, and buttons on the gear-shift that are new to us. The most important gauges are the Tachometer, Engine Temperature, Exhaust Gas Temperature (EGT, or Pyrometer by name), and Temperature Gauges for the transmission and differentials. Using these gauges, the experienced drivers can “balance” the operating conditions in their rig to match any road conditions that our highways can throw at them.
What I am going to discuss here is this term “balance,” because this is the key to operating your rig without blow-ups and break-downs! I am making the following assumptions:

Important Concepts to Understand

Unlike gasoline engines, diesels do not necessarily work harder by pressing harder on the accelerator! A gasoline engine will happily work at full throttle (at least for a short period of time), but a diesel usually just wastes fuel at full throttle. The output you get from diesel engines is dependent upon the following:

• RPM - Every engine has a range of RPM where it produces power most efficiently, or as we tend to say, where it “likes to work.”
• Fuel/Air mixture - At a given RPM, an engine, even with the help of a turbo-charger, can only “pump” a given volume of air into the combustion chamber. This volume of air can combine with only so much fuel efficiently, so it follows logically that feeding more fuel to the fire will simply waste fuel.

Weight requires energy to move it. If you apply a small amount of energy, it will take a long time to see results. Conversely if you want to change the speed of a mass quickly, it will take a massive input of energy. Thus acceleration of heavy vehicles involves inputs of large amounts of energy from your engine and once at speed that energy is resident in the moving vehicle. To decelerate we must take that energy away from the vehicle and the brakes are the main tool we have to absorb all that moving energy. We burn fuel to create the heat needed to move the load and that energy becomes heat again when we slow the load using the brakes. Just as the engine can only produce motive energy at a certain rate, the brakes can only absorb it at a certain rate.

We must learn what those limits are and operate our vehicles within those limits.

The Accessories you will NEED to be an Informed Driver

The Tachometer indicates how quickly the engine is spinning. The usual measurement is Revolutions Per Minute, or RPM. The Tachometer shows us at a glance whether we are operating the engine within its best working limits.

The temperature of the exhaust (referred to as EGT) leaving your engine is a valuable indicator of how efficiently your engine is working. Steady temperatures that remain below 850-900 degrees Fahrenheit indicate that your engine is using the fuel and air mix efficiently. Rapidly rising temperatures, or temperatures that are above 900 degrees indicate that “the fire” is migrating down the exhaust pipe and doing absolutely nothing towards keeping you moving. Serious damage may occur in the engine if the driver allows this condition to get out of hand. This gauge is commonly called a Pyrometer, or Exhaust Gas Temperature (EGT) gauge.

Engine Temperature is another vital clue to conditions in your power-train. A climbing engine temperature gauge is never good news...make sure you find the reason quickly!

The temperatures in the transmission and differential are indicators of how well these components are coping with the energy being delivered to them by the engine. If they are receiving more energy than they can transmit to the wheels, rapid heat build-up will occur. In most cases this heat is the result of slippage. Slippage can destroy the transmission (or the clutch in a standard) in no time at all. Without a gauge to monitor transmission temperatures, you may have your engine working away happily, but discover too late that your transmission has been “losing its grip!”

Other accessories are available, and you can select from them as you feel the need, but keep in mind that the gauges mentioned above can tell you all you need to know.

Normal driving techniques

Under normal driving conditions, the driver should monitor the exhaust and transmission temperatures to achieve the lowest temperatures possible that provide the desired speed down the road. After a while, these temperatures will become your benchmarks. Significant deviations will become warnings to you that an adjustment, or even maintenance is needed. You will also learn that the rig will run more efficiently under some conditions in a lower gear and yet at other times it will run better in the higher range. For example, consider the fact that diesels tend to dislike excessive humidity. In conditions like this, you will often find that a lower gear is required to provide optimum operating temperatures.

This constant fine tuning of the balance between the gear selected, and the EGT will pay you dividends when you pull up to the pumps! My rig has a GCWR of 20,000 lbs., and averages 11.5 to 14.5 mpg (Imperial gallons). On cruise, the mileage is noticeably lower!

Mild grades are another place where drivers can save fuel. I make a habit of driving slightly below the posted limit when the road is perfectly flat. On slight downgrades, allow the speed to move up to the posted limit...especially if you can see an incline beyond it. I call this “putting some energy in the bank”. This energy is carried into the incline and often is sufficient to carry the rig over the top without adding any more fuel to the fire. All I have done is trade the (speed) energy gained on the down-slope for the climb to follow.

Techniques for pulling with Automatic Transmissions

Today’s automatics are a joy to drive, saving you a lot of stick-stirring and clutch stomping. (If you are tired of shifting, as I am, buy an automatic!) Automatic transmissions benefit the most from having a temperature gauge installed. When you have this sensor installed please note that the sensor for this gauge should be mounted as close to the transmission as possible. The more remote the sensor is, the older the information will be at the gauge...meaning that you may read the demise of your gear-box after it is a fact!

Most automatics today have a mode for forward gears commonly referred to as “lock-up”. In this state, the torque converter is not “slipping” and while in this mode, it is not generating nearly so much heat. So long as your transmission remains in lock-up, you will find that you can work your engine to its maximum potential. Beware, however, for when the transmission encounters a loss of speed, or increased load it will shift out of lockup and the internal temperatures will sky-rocket unless you act quickly.

It is vital that you learn to recognize when your transmission has not achieved lock-up. The first indicator will be higher RPM than normal for the speed and gear selected, the second will be a rapid climb in transmission operating temperature.
When you detect the loss of lock-up you need to discipline yourself to do three things:

It is important to ensure that if the lower gear you have selected has a lock-up mode, that you re-apply enough throttle after downshifting to cause the transmission to enter this mode. If the transmission does not engage lock-up, you must immediately begin power-train conservation tactics!

If the transmission will not shift into lock-up, you must immediately reduce the engine EGT to 650-700 degrees by reducing throttle. With the engine working more easily, the transmission will be able to cope better with the additional heat from the torque converter. Of course you will slow down, but a slow climb is far preferable to a “blow-up” climb! Continue to monitor the temperature gauges and your speed to ensure that everything stabilizes within safe limits. I have listed the temperatures that are good in my Ford. You will need to determine the ranges where your vehicle works best by driving long grades in a way that these temperatures will remain stable for the duration of the climb. Most rigs will work happily in the ranges I quote here.

Component Operating Range

• Engine: 1400 to 2700 RPM, with 2100 RPM being the “sweet spot”.
• Transmission: Below 220 degrees.
• EGT: Below 900 degrees, 650-700 when the transmission is out of lock-up.

Standard Transmissions

Your tour of the highway tractor’s office will reveal a lot of extra knobs on the gear-shift. I am not going to detail what each knob is and does other than to say they allow the driver to select gears so that the engine is always at the RPM range where it works the best.

Our transmissions, with four or five gears, tend to test the engines’ ability to get back to its “sweet spot”. Happily most small trucks have engines with wider usable RPM ranges than the heavy industrial engines found in the big rigs. Your biggest chances for problems come from two sources, riding the clutch and missing a shift.

The answer to riding the clutch is do not do it — under any circumstances! As to missing a shift, everyone does it, but by thinking well ahead and watching the road carefully, we can avoid last-minute panic shifts that have the greatest chance of being the ones missed. When you see a grade coming, try to assess how steep and long it is before you begin to climb or descend. Get ready early for long climbs. Be prepared for the speed to bleed off and make slow, deliberate shifts as you enter the speed range of the lower gears. Keep the EGT at the 850 degree range by reducing throttle as speed declines. For descents, slow down and get into the gear below the one you’re sure will do the job. The shift most likely to be missed is the downshift on a descent, so avoid it if at all possible. By down-shifting early you reduce the need for multiple shifts as you descend. If you must down-shift, be aware that your speed will build rapidly as soon as you release the clutch. To compensate, bring the engine speed up at least 500 RPM higher than needed for a normal down-shift.

Mountain Driving

Become an avid sign-reader in mountainous terrain. More importantly, do what they say! These signs are ideal for vehicles of our type, especially those of us operating near our GCWR. The speeds posted for curves and grades have been tested with high GVW vehicles in mind and assure you safe passage under normal weather conditions. One of the most important signs for us to heed is the grade severity indicator. Most highways will indicate the length and “percentage” of the grade and will suggest procedures for slow-moving vehicles.

Long, Steep Climbs

When people see a semi-trailer creeping up a hill, most people assume that the driver is “standing on it” and praying fervently that something does not fail. Nothing could be farther from the truth. In reality, the driver has achieved a “balance” for that grade where the speed over the ground (gear selected), engine RPM, EGT and power-train temperatures are all stable within normal operating limits. The entire unit is working quite happily!

You can achieve the same happy balance with your rig with just a little practice. Learn to back off the throttle when a temperature indicator shows a rapid climb, or creeps above efficient operating levels. The reduced speed will allow you to gear down, giving the rig more leverage for the job at hand. This increased leverage will give you room to reduce the EGT and transmission temperatures back into the ideal range. Do not be tempted to gear up too quickly if a long climb eases up temporarily...take this as a chance to ease up a bit more and give your rig a much earned breather.

IMPORTANT SAFETY TIP: If your speed degrades to the point where you are moving significantly below the posted speed, select your four way flashers. Take advantage of pull-outs if traffic is building behind you, your courtesy will be appreciated. Once you are in the pull-out, take a break. Let the engine idle to allow the exhaust (and the turbo, if you have one) to cool. While this is happening, your transmission will also cool. Monitor the gauges and enjoy the view, stretch your legs and sip a soda while you wait!

Long, Steep Descents

On down-grades, a Brake Check area is often provided. Pull in and park, using normal braking. Activate your four-way flashers and immediately walk around the vehicle ensuring that:

I carry a small hammer and “thump” the duals on the truck and the tandems on the trailer. So long as the sound produced is the same on each tire, they are near the same pressure. After this I cautiously place my hand on the wheel near the center to assess the temperature of the brake and axle. If you sense a lot of heat radiating before you contact the wheel, you have a problem. Let it cool and determine whether the brakes are adjusted too tight, or whether you have a wheel bearing about to fail. Now is the time to catch these problems...before you’re on your way down-hill!

If all wheels are equally warm to the touch, and not excessively hot, you can test your brakes. Apply the trailer brakes and tug firmly with the truck. Next, roll ahead and apply the truck brakes. You can now pull the trailer emergency brake (Breakaway) switch and repeat the tug test to ensure that the trailer emergency braking system is operational. Having done this, leave the brake check area with your four-ways on and your transmission in the gear that will best assist in maintaining the suggested speed for the grade. If you have an engine braking system, or exhaust brake, select it before you enter the descent.

Tractor-trailer units augment their engine braking by applying steady pressure to the brake pedal. The amount of pressure applied is designed to maintain a safe speed. The driver can apply braking for an entire descent so long as the brake shoes are not forced to absorb more heat than they can dissipate into the air. As the heat increases, the braking efficiency decreases.

Tractor-trailers have brakes that are applied by air pressure in the brake lines. This has the advantage that the driver can apply pressure to the brakes for extended periods without experiencing “spongy pedal”. The brake shoes can still overheat and lose efficiency, but the reduced braking experienced will not be so dramatic as in a hydraulic system. Our trucks do not have air brakes. The brake fluid can boil if too much heat is allowed into the system resulting in the sickening feeling called “spongy pedal”. To avoid this we can “pump” the truck brakes, allowing them to cool between applications. At the same time we can maintain steady braking on the trailer by activating the hand control on the trailer brake system. The same rules apply here, do not expect the brakes to absorb more heat than they can dissipate into the air. It will take you some time to learn how much pressure can be sustained on your trailer brakes. In the meantime, extra caution in the form of lower speeds downhill will be your biggest safety-net. Always make your decision to slow down early.

The old adage, an ounce of prevention is better than a pound of cure, is especially true for operators of high GVW vehicles. Your best safety net is between your ears...always look and think ahead as you drive.

Observe what is happening around you and plan your response well in advance.

Remember, your speed represents a lot of energy that can’t be dissipated in the same reaction times enjoyed by the smaller vehicles around you.

Always be aware that more weight equals more momentum and plan your stops accordingly.
Life is good...let’s take the time to ensure we enjoy it! n