Black Fuel & More

Here at Pittsburgh Power, we have recently had two trucks in our shop that were suffering from Asphaltene, or black fuel, which is caused by hot fuel returning to the fuel tanks. The little black specs that make the fuel look black are actually the diesel fuel trying to revert back its original asphalt base. Ultra low sulfur diesel fuel is low in oxygen and nitrogen and problems develop with the fuels’ thermal stability when the hot fuel returns to the fuel tank. Once the little black dots collect in the fuel filter, it will cause the engine to lose power and/or shut down.

During the summer, you are better off keeping your fuel tanks as full as possible to try and dissipate the heat and avoid black fuel in your tank. There is a chemical available to treat this condition, so if you see your fuel starting to darken, give us a call and order a quart before you have to drain and clean your fuel tanks. When we first came across this problem, we thought it was a bad case of algae, being algae is mucus-like and has small black specs in it. It’s hard to see the mucus because it lives off the moisture in the bottom of the fuel tank. The easiest way to tell if you have algae or Asphaltene is the color of the fuel – dark or black fuel is Asphaltene and clear with little black specs is algae.

For the past year, we have been doing the MD Alignment here in our shop, which aligns the rear axles with the steering axle. We have found that the AirLiner rear suspensions on most of the Freightliners have a shifting problem with the manner in which the spring is mounted to the axle. It’s most prevalent on the rear axle of the drives, and the result is that the air bag is not in the proper alignment with its base (see photo). Jack, our Cat mechanic and alignment specialist, has developed a tool to realign the base of the air bag with the top mounting plate. For the suspension to work properly, it must be in alignment. When the air bags are not in alignment, the rear of the truck will sway slightly, causing the steer tires to have accelerated wear. This problem can be repaired in about two hours and $120 in parts.

Now, let’s shift gears to turbocharger failures on high-performance engines. You must have a light foot on the throttle pedal when you accelerate or you can burn through the thin layer of oil on the thrust washer. When this happens, the thin clearance between the compressor wheel and the housing will diminish even further and the wheel will hit the housing. Now, your turbo is junk and you’re upset, and there isn’t much we can do about it. The turbo manufacturer will take the turbo apart, and when they do, it’s very clear to them that the turbo was over-sped.

Remember the “egg under your foot” analogy I have spoken about in the past? You must drive as though you have an egg between your right foot and the throttle pedal. I have been driving the same Dodge Cummins pickup for 20 years with the original turbo and yes, the truck is turned up (about 150% over stock), and I have never had to replace the turbo. I’m very gentle with the throttle and I also have two other turbine housings I install on the turbo depending on what altitude the truck will be operating in. The larger turbine housings slow down the RPM of the turbo and allow the engine to breathe easier because they flow more exhaust. Now, I realize that you can’t keep changing your turbine housings on your semi, but you can be lighter on the throttle.

A turbocharger is like a vacuum cleaner sucking in air – the faster the rate of acceleration, the more pressure is put on the thrust washer which holds the turbine wheel, shaft and compressor wheel in place. The thickness of the layer of oil on these parts is only half a micron (very small). With excessive heat and pressure, it’s possible to burn through the oil, and that is when the damage starts. Also, years ago, every driver was taught to allow their truck to idle for about two minutes to cool down before shutting it off. People don’t want to do that today and some have been told by salesmen at dealerships that it is no longer necessary because the computer will take care of it. The computer has NOTHING to do with the heat in a turbocharger, and YES, you still have to allow the turbo to cool down before shutting off the engine!

The oil not only lubricates the bearings, bushings and thrust washers in the turbocharger, but it also cools it down, too. If you don’t have a pyrometer, which you should have, then at least give the engine one minute of idle time to cool down before shutting it off. If you just pulled a mountain and then stopped, you should give the engine at least three minutes to cool before shutting it off. The turbo is the lungs of your engine – please treat it with respect and kindness. If you have any comments or questions, I can be reached at Pittsburgh Power in Saxonburg, PA at (724) 360-4080 or via e-mail at bruce1@pittsburghpower.com.