Fresh air

Maintain your air cleaner to keep your engine running better, longer.

One of the most important discoveries early engine designers made was that engines would last much longer if the intake air was cleaned. Dust in that air ended up in the oil, where it formed a potent grinding compound that ruined entire engines – and it still can.

The air cleaner has a lot of air to clean. A Caterpillar C15 engine at 1,500 rpm, even under light-load cruise conditions with little turbo boost, will fill the entire volume of its cylinders (928 cubic inches) with a fresh batch of air at least 12.5 times a second. The engine at this rpm will use more than 6.7 cubic feet of air per second. When accelerating or hill climbing with high boost pressures at this rpm, it will ingest air more than twice as fast as that. And all that air has to be at least 99.9 percent clear of dust. That’s why maintaining your air cleaner and the associated intake piping is so important.

At Hunter Keystone Peterbilt in Lancaster, Pa., Service Manager Ray Jakubus and shop Formean Dave Brown know how to service several different types of air cleaners.

Single or duals
Many modern aerodynamic trucks have a single air cleaner mounted under the hood. These can be quite easy to service but may not offer a lot of capacity for dirt. Older, more classically styled trucks often have dual chrome or stainless air cleaners situated on either side of the cowl. These offer a much larger volume of space for the air cleaner cartridge. By having two units plumbed to supply equal amounts of air to the engine, they don’t have to be so frequently serviced.

Another advantage of dual cleaners is low restriction. The air cleaners take a very long time to clog with dirt, and the lower the restriction, the better a late model engine will perform and the better the fuel economy will be.

Precautions for maintenance
Careless air cleaner maintenance can actually increase engine wear.

First of all, the engine must always be shut off throughout the procedure. The keys should be removed so no one can start the engine accidentally. Not only will a running engine draw in dust that will tend to accelerate wear, there is a good chance an object like a rag near the air cleaner could be sucked into the air intake and become very difficult to remove.

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Precautions should also be taken throughout the procedure to prevent dust anywhere on or inside the housing from being allowed to enter the intake piping downstream of the filter cartridge. Wipe off the outer housing where the cap or other covers will be removed. Also to be sure to wipe off any dust that may fall off the filter cartridge into the air cleaner housing or associated piping before replacing the cartridge and closing the housing back up.

It is also important throughout the procedure to inspect all seals and hoses for leakage of any kind.

Doing the job
On a traditional Pete 388 with external dual chrome air cleaners (A) and a Cummins ISX engine, one of the most effective ways to judge when it’s time to service an air cleaner is by checking the restriction gauge. On this truck (B) the gauge is dashboard mounted. Brown says the air cleaners on this model have so much capacity you’d probably be smart to replace them when the restriction gets about 3/4 of the way to the red line. With this type of gauge, you need to read the restriction when the engine’s airflow is at the maximum – that is, when under maximum load and running at maximum rpm.

The reason for replacing the cartridges early is that they last so long their seals or filter medium can deteriorate even before the filter is clogged. Leaking seals or a defective medium can let a lot of dust in.

In fact, it’s ideal to remove and inspect air cleaners at every major maintenance interval – every second or third oil change, Brown says. This ensures problems will be corrected before significant damage is done.

Some trucks will have a different type of restriction gauge, located under the hood (C). This gauge will record the maximum restriction so you can read it when the engine is off. If the slot on the side is entirely red, the air cleaner needs servicing. The slot will have both yellow and red in it when approaching maximum allowable restriction, indicating the need to service the unit soon.

All Peterbilt air cleaners have a squeeze bulb at the bottom (D). This serves as a water and debris drain. Every few days, squeeze it and hold it open until completely drained.

Servicing an external air cleaner

  1. The top is attached with spring-loaded attaching washers. You can peer through the strainer at the top to see which way to turn it (E). On this one, it’s turned counter-clockwise. Rotate the top to bring the retaining washers in line with holes at the ends of the mounting slots, then lift it off. Place it in a spot where its polished top surface won’t be damaged.
  2. Remove the capnuts (F) that retain the intake air screen and cartridge retaining ring. Use a socket wrench to loosen them and then remove them. Remove the intake air screen.
  3. Remove the polished aluminum cartridge retainer. This may stick to the rubber seal on the top of the air cleaner housing. If so, use a rag to protect your fingers and go around the lip pulling upward until it comes loose (G), then remove it.
  4. Grab the cartridge along the inner edge of the seal and pull upward to remove it. It may help to reach down and grab it by the bottom (H). Wiggle it back and forth to loosen it.
  5. On this model, the mirror sits too close to the cartridge to allow clearance for removal. First, unbolt the mirror bracket at the top of the door. Then loosen the bolt at the bracket where it connects to the upper mount right by the windshield. Rotate the mirror slightly to the rear.
  6. Remove the cartridge (I). Inspect it and the black rubber seal on the top of the housing for dirt tracks, which indicate a bad seal or distorted retainer. Inspect the seal to make sure it is intact and pliable. If it has begun to harden or crack, replace it. If the rubber seal on top of the cartridge shows dirt tracks and is cracked or hard, replace the cartridge.
  7. If the cartridge is obviously plugged full of dirt, replace it. If discolored but not caked with dirt, drop a lamp down inside the cartridge and see if light will shine through the filter medium. If you can see light, the cartridge can be reinstalled. If there has been a recent, large jump upward in the reading on the restriction gauge, the unit should probably be replaced.
  8. You should also carefully inspect all the intake air piping and clamps between the air cleaner and turbocharger (J, K). Any leaks in this part of the system will result in dirt ingestion. Brown says drivers sometimes step on the air intake piping, which can cause it to be damaged by the engine cam cover or other parts, resulting in a large leak.
  9. The new cartridge must be replaced with the small drain hole at the bottom. Slide the cartridge down into the housing, then press it with both hands to help insure a good seal.
  10. Install the cartridge retainer (L) over the studs on the top of the unit and press it downward so it will seal.
  11. Install the intake air screen over the studs. Then install the capnuts (M). Tighten them to a low torque in several stages in a criss-cross manner with a socket wrench.
  12. Install the polished aluminum cap by first positioning it so the attaching washers will slide through the holes, forcing it downward so the washers slide through the holes and turning it clockwise until it sets and is locked into position (N).
  13. Rotate the mirror so the rod connecting it to the door can be reconnected. Install the nut and bolt, then tighten the bolt that fastens the upper part of the mirror bracket to the small mounting bracket near the top of the windshield.

Servicing underhood air cleaners
On a more aerodynamic Pete with an under-hood air cleaner, you can see the drain system’s squeeze bulb under the chrome pipe (O). The small black hose leads from the turbocharger side of the air cleaner to the restriction gauge on the dash.

  1. First unfasten the three clips for the black cap located on the turbocharger side of the air cleaner (right side of the truck). Then remove the cap (P).
  2. Next, simply pull the air cleaner out of the housing (Q). Note that the cartridge had a larger diameter that must go into the housing first (R).
  3. To look up the part number, see the label inside the cap. Note also the rubber ring seal in the cap and make sure to inspect it for cracks and brittleness. Replace it if necessary.
  4. Check inside the housing for any signs of dirt leaking from the outside of the unit to the center of the filter, where it should be very clean. Replace parts as necessary.
  5. Insert the new cartridge, big end first (S). Center the cap on the outer end (with the smaller diameter), raise it into position, install over the housing, and hold while reengaging the three clips (T). Make sure to inspect all the intake piping between the air cleaner and turbocharger for leaks, which would allow dust to enter.

A Peterbilt 387’s air cleaner is also mounted under the hood. It takes air in through an opening on either side of the hood and sends it to the intake on the top of the air cleaner housing through a crossover duct located on the inside of the hood (U). The round fitting on top of the housing seals with a similar hole in the crossover duct. While leakage between the housing and duct would not allow dirt into the engine, it would cause hot under-hood air to be drawn in, which is undesirable. If there is any sign of deterioration or wear of the housing, it should be replaced.

Changing the cartridge in this type of air cleaner is similar to what was done above.

  1. Loosen and then unscrew the three thumbscrews by hand and remove them. Hold the cap on with one hand while removing the screws. Once removed, place the cap and screws in a safe spot where they won’t be kicked or knocked to the ground.
  2. Slide the cartridge straight out.
  3. Note that there is a label on the bottom of the housing that gives the replacement part number.
  4. Inspect the cartridge. In this case, it’s obvious that the air cleaner was still working well as the inside surfaces are still quite clean and there are many open areas on the outside. However, there is quite a bit of dust caked in certain areas on the outside, which will cause restriction after a few more miles. Brown ultimately recommended replacement to the customer.
  5. This cartridge is replaced with the open end facing inward and the closed end facing the cap. Air will then flow through the walls of the cartridge into the center, then out through the opening in the cartridge and into the turbo air intake hose.
  6. Replace the cap with its holes lined up with the threaded holes in the housing. Install the three attaching nuts. Tighten alternately in a criss-cross pattern with your fingers only until snug.

The Donaldson Co. workbook on basic filter maintenance mentions air pre-cleaners. Trucks used in construction and agriculture sometimes have a section of the air cleaner that uses centrifugal force to sling dust out of the air before it lodges in the filter medium. This type of air cleaner housing should be disassembled and thoroughly cleaned out prior to servicing the filter medium.

Also, it’s critical to use either OEM parts or aftermarket parts that are of high quality and fit properly.

For More Information:

Hunter Keystone Peterbilt
(800) 243-2458

Donaldson Co.
(800) 792-8135

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