Their acronyms may sound alike, but the care and attention required of DPFs and DEF are very much different.
Diesel particulate filters (DPFs), of course, have been on all new trucks since 2007. Their job is to trap and then burn off particulate matter at high temperatures. Diesel exhaust fluid (DEF) is a new requirement on 2011 model year trucks using selective catalytic reduction (SCR) to eliminate NOx emissions. The new fluid is housed in a separate tank on the frame rail and is injected in small doses into the SCR catalyst, where it sparks a chemical reaction that converts NOx into harmless water and nitrogen.
Both DPFs and DEF are pollution-busting tools, but the similarities end there.
The recent Canadian Fleet Maintenance Seminar included a working session on the care requirements of both items, detailing how drivers and maintenance managers can ensure they get the most out of their costly aftertreatment systems.
Dealing with DEF
Unless youÕre buying an International, any new truck you purchase from here on out will come with SCR and require DEF to function properly. Contrary to early rumours, DEF isnÕt a toxic substance. You donÕt need rubber gloves, HazMat suits or gas masks to handle the fluid. ItÕs a mixture of urea and demineralized water that must be injected in small doses into the exhaust stream to trigger the chemical reaction that breaks NOx into harmless vapour.
While the fluid is not hazardous, Mack Trucks CanadaÕs Steven de Sousa, said there are things drivers and maintenance managers must be aware of.
They say cleanliness is next to godliness, and the same holds true for the SCR system. The biggest mistake a driver or maintenance manager can make is to put something other than DEF into the DEF tank. OEMs have gone to great length to prevent this, including putting a universally-coloured blue cap on the inlet, making the inlet too narrow into which to fit a diesel pump and in MackÕs case, magnetizing the opening so it will only accept the appropriate fluid from dispensing equipment.
ÒMake sure you donÕt put anything other than DEF into the tank,Ó de Sousa warned. ÒNo straight water, oil, gas and donÕt use unapproved containers. ThatÕs whatÕs going to kill us here in the industry, if you use an old funnel you used for coolant or oil, thatÕs going to cause issues.Ó
Most DEF is currently sold via plastic tote jug that comes complete with its own single-use funnel.
Another thing to keep in mind is that DEF is corrosive, which is why all truck makers provide plastic DEF tanks.
If dripped, Òit will stain aluminum fuel tanks,Ó de Sousa warned. ÒJust wash it off with soap if you spill it on yourself, itÕs not going to hurt you. If you spill it on paint, donÕt scrub it off. Dab it off lightly and rinse with water and soap. It will damage the paint if you leave it on there.Ó
If left to dry on its own, DEF will turn into a white, powdery substance, which is a good indicator of a DEF leak and something drivers should watch for when conducting their pre-trip inspections.
ÒDrivers, on their pre-trip should just have a look for leaks,Ó de Sousa suggested. ÒLook at the pump, the pump connections, the injector, the exhaust connection from the DPF to the SCR catalyst and look for leaks around the band clamps. Look for a wet stain around those areas or for the white stuff.Ó
The only maintenance item on an SCR system is a filter underneath the inlet cap, which needs to be replaced every 3,000 hours or 100,000 miles. The filter costs about $30 so de Sousa recommends erring on the side of caution and replacing it early until there is more experience with the filter in real-world operating conditions.
ThereÕs also a rock screen in the fill neck, which should be monitored and cleaned as required.
DEF dilution should not be an issue, but if for some reason old DEF thatÕs past its best before date is added to the tank throwing the dilution off and triggering the trouble light, customers should take their truck in for service and have the dealer measure the concentration. TheyÕre equipped with special tools for just this purpose and in most cases, the problem can be solved by topping the tank up with fresh DEF.
In a worst case scenario if something other than DEF is put into the DEF tank, de Sousa said thereÕs a drain plug underneath the tank.
ÒDrain it on your lawn and youÕll have a nice new patch of grass there next summer,Ó he said. ÒIf nothing else, itÕs a very expensive fertilizer.Ó
After draining the tank, it should be washed with non-sudsing detergent and rinsed until the water is completely clear.
Drivers may notice a pump running for about four minutes after they shut down an SCR-equipped truck. Upon shutdown, the system reverses the flow of the fluid, drawing it back into the tank to prevent it from freezing in the lines. DEF freezes at -11 C, but as long as itÕs in the DEF tank it wonÕt cause any damage and it will quickly thaw when the engine is restarted.
The other potential mistake – which seems unthinkable but actually became problematic in Europe where SCR has been used for years – is the use of home brew DEF.
ÒIn Europe, some guys thought they could make their own stuff,Ó de Sousa said. ÒThey got a buildup of residue with non-API certified DEF. You get deposits and the catalyst is useless and youÕre basically looking at a replacement cost of about $6,200 each.Ó
It should go without saying that API-certified DEF is a must and you can identify it by the black seal of approval on the jug. If you come across DEF that isnÕt labeled with the API seal, de Sousa suggests asking some questions of the supplier.
Inside the cab, drivers will notice a new gauge indicating DEF fluid levels. On Mack trucks, itÕs directly across from the main fuel gauge.
ÒMake sure drivers know that,Ó de Sousa said. ÒWeÕve had drivers think it was the left hand (fuel) tank and right hand (fuel) tank and they didnÕt get too far with it.Ó
If DEF levels reach less than 12% of the tankÕs capacity, a dash light will appear along with an audible alert and a warning will appear on the in-dash message centre. Numerous other warnings will occur before DEF levels reach 0.1%, at which time the engine will be derated by 25%, which should get the driverÕs attention.
When DEF runs out completely, a new set of warnings will appear to let the driver know the engine speed will soon be limited to 5 mph. If the driver, for whatever reason, fills up with fuel but doesnÕt add DEF, the truck will be limited to 5 mph, just enough speed to limp to a DEF supply.
While some driver awareness is required, de Sousa said thereÕs nothing to worry about as long as the SCR system is kept clean and the filter is replaced periodically.
ÒItÕs nothing to be afraid of,Ó he said. ÒKeep it clean and stay on top of the maintenance of the filter and this thing is going to save you fuel like you wouldnÕt believe.Ó
Dealing with DPFs
Truckers already have several yearsÕ experience with DPFs, so by now they should be comfortable with the filters, which are responsible for the elimination of particulate matter or soot.
However, even after three years in the field, Norm West of DPF Cleaning Specialists warn many DPFs are being grossly neglected.
Engine OEMs have promised cleaning intervals as long as 320,000 kilometres, however West says they should be cleaned once a year in over-the-road applications and every nine months in vocational applications that involve lots of low speeds and stops and starts.
ÒWe recommend (cleaning) from what we see from the end userÕs point of view once a year, thatÕs minimum,Ó he warned. ÒIf running vocational, maybe every nine months because they are being abused.Ó
As a third-party cleaner of particulate filters, West has seen all types of damage. Much of it was avoidable. For starters, he advises customers to get on top of DPF issues early. He says customers should keep an eye on the condition of connections to ensure theyÕre in good shape. Using a Krown T-40 on connections will help eliminate corrosion and other damage, he noted.
West also said owner/ops or maintenance managers should take resistance readings across the temperature sensors and look for consistency. If the readings vary, ÒthereÕs something wrong with the temperature sensors.Ó
Drivers may be able to detect potential DPF problems from behind the wheel.
ÒThe first indication theyÕll give you is ÔIÕve gotta drop a gearÕ,Ó West said. ÒThatÕs the first complaint you will get from a driver. If they have to drop a gear going up a long hill, theyÕre going to complain. By the time he does that, the DPF and the oxidation catalyst are already failing.Ó
Other symptoms of DPF problems may include poor fuel mileage and black smoke being emitted from the smokestack. If thereÕs an underlying cause of DPF damage, it should be fixed before the filter is cleaned and replaced.
ÒItÕs not advantageous just to take the filter out, fix it and put it back in and have the same thing happen again,Ó West pointed out.