Maintenance Q&A – October 2020

Getting trucks back on the road; cabin air filters

October 2020

Paul Abelson


Q. My partner and I own a small fleet. We never had more than 20 trucks and usually fewer. He likes Kenworths, and I like Petes, and that’s all we have in the fleet. They all have Paccar 500s and Eaton transmissions. We pull other people’s trailers, so that’s not a problem. We do some minor maintenance on the trucks when we can but mostly we drive, so most of the work gets done at the dealers.

Because of the recent slowdown, we had to park six of our trucks. They have been down for about five or six months. Now business has picked up and we’re ready to put the trucks back in service. What do we need to do to get them ready?

A. That’s good news that I hope other readers are facing, too. The question is complex. I’ll address things to check in no particular order, as all need attention before you’ll be ready to go.


Your tires have been sitting and have probably lost air. Rubber is porous, and tires can lose about 3% of their air pressure each month. Assuming they were at full pressure when you parked them, the tires can be dangerously close to overheating when you are at highway speed. Look up the proper air pressure and re-inflate for the load you’ll be carrying. You can find load-inflation tables for your make, size, and load rating of your tire on the internet. While you are at the tire, check for any uneven tread wear, sidewall damage or signs of flat-spotting.


We had some heavy weather while your trucks were down, and even though they were not on the road exposed to corrosive salts there may still have been corrosion damage from spray and humidity. Check any exposed connectors, especially at the seven-pin connector and any lights. Check battery cables and terminals at the starters and charging systems. If you have not connected the batteries to trickle chargers, they are most likely run down, and the plates may be sulfated. Using a load tester, check the batteries’ conditions. A plain voltage meter will not read its ability to start an engine.


While your trucks were sitting, seals and hoses may have dried out, and fluids may have leaked. Check your truck and the ground beneath it, especially at all fluid couplings. This includes filter mounts and hose clamps. Check hoses for cracks or soft spots. Check fluid levels, including oil, coolant and driveline lubrication. Unless you are using pure synthetic oil, your engine oil may have oxidized over the six months. It’s a good idea to change oil before putting your trucks back in service, but whether you change oil or not consider replacing filters. They will quickly be collecting any debris or sludge when you start your engine. Then change them again after about 500 miles. Always pre-charge all new filters with the appropriate oil or coolant.


Diesel fuel, including biodiesel, is more subject to oxidation than lubricating oils. And over five or six months, water will have condensed in the tanks. Fuel provides nurturing environments for colonies of slime from fungus and algae. As slime goes through the fuel system, it clogs filters, causes injectors to stick, and creates deposits on injector tips, altering the fuel spray patterns.

Check fuel tanks for condensed water, slime and sludge. After long storage you’ll probably need to drain the tanks and refill with fresh fuel. Because of this organic growth, you should treat your first fill with a multipurpose fuel treatment. Use a biocide. Read and follow directions and warnings on the label, since biocides can be toxic. There are also leading brands of fuel treatments that control water, clean the fuel system, lubricate injectors, and inhibit organic growth. Because injectors may stick, consider sending them out for testing, cleaning and calibration.

Your fuel filters probably have sludge on them and will need changing. Don’t forget to pre-charge the filters with new fuel.


Over the months of sitting idle, your oil has drained from piston rings and cylinder walls. With injectors out, squirt some engine oil through the openings into each cylinder. Then crank the engine slowly by hand or in very short bursts with the starter. This will spread the oil on the cylinder walls, preventing the engine wear that occurs with dry cranking. Reinstall the injectors, and you should be ready to start the engine. While idling, check for bearing noises and slipping belts.

That covers the special attention needed for the drivetrain. Before running, do your normal pre-trip inspection. Make sure your air system, brakes, steering, lighting and all other systems are safe and good to go. Glad to hear your business is picking up.

Q. I have a 2014 Cascadia that I bought two years ago. I try to buy 4-year-old trucks and keep them six years. I do most minor maintenance, but I’m on a job that has me away for a long period. I took the truck to a Freightliner dealer for an oil change and all that goes with it. I do it as close to 25,000 miles as possible. The dealer asked me if I wanted the cabin air filter changed. I didn’t know I had a cabin filter. My previous truck, a 2008, didn’t have one that I knew of. Is this something I should do?

A. Yes, especially with COVID-19 going around. Anything that will keep the air you breathe more germ-free should be used. Freightliner didn’t put cabin air filters on Cascadias until model year 2009.

While COVID-19 is much smaller than the particles the filter will remove, the virus travels on water droplets which can be large enough to be trapped.

It’s easy to change the filter. On the passenger side firewall is the filter housing. Remove the two Torx screws and lift the cover. Reach inside. The filter element slides out easily. Replace and reinstall it.

Be careful handling the filter element. Wear gloves. It may

have the coronavirus or other biohazard material on it. Place it in a sealable bag, and dispose of it legally. The filter should be changed when you winterize and prep for summer. LL


Paul Abelson, senior technical consultant, is a longtime contributor to Land Line. He’s a member of the Society of Automotive Engineers and a member of the Technology and Maintenance Council. In 1995, TMC awarded him its Silver Spark Plug award. In 2006, he received the Lifetime Achievement Award from the Truck Writers of North America. Although he’s “retired,” he still makes a popular contribution to Land Line readers with “Maintenance Q and A.”