Auto Q&A: Heading off valve buildup in Subaru Forester
"I have read about folks installing 'catch cans' in the PCV system to condense and trap oil and water vapor."
Q: I own a 2019 Subaru Forester. It has a direct injection engine. DI appears almost unavoidable now. I am very happy with my new Forester but am wondering whether there is anything I can do to ward off the valve buildup that seems to be inherent with this design. I’m not sure whether automotive engineers have figured out how to prevent this issue.I have read about folks installing “catch cans” in the PCV system to condense and trap oil and water vapor, theoretically preventing them from going back into the intake and causing buildup. What is your opinion of these devices? Would installing one create issues for me when I take the car in for service at the dealer (i.e. avoid claims that it violates warranty)?I would like to avoid or at least delay the seemingly rather major job of pulling apart the intake side of the engine to clean and remove buildup every 60,000 miles or so.— G.W., ChicagoA: If it were as simple as installing a catch can, don’t you think that the automobile engine engineers would have thought of it first? I would advise against it and, should engine damage occur, it might void your warranty. Pulling the cylinder head is a costly service, but I know of no shortcuts.Q: I drive a stick shift. When parking, I usually leave it in neutral and just set the hand brake. In the winter, the brake often sticks and doesn’t release until I start driving. Would it be better to leave it in gear and park without setting the parking brake when it is cold out?— M.C., ChicagoA: The sticking problem may be more pronounced when the weather is near freezing and the moisture on the rear brakes freeze. Although I would still set the brake, you can get away with putting the transmission in gear, as long as you are not on a hill.I suggest using reverse. The gear for reverse usually has square cut gear teeth instead of the helical cut on the forward gears. As such, it is less likely to allow movement.Q: I have always wondered what are the advantages of a passenger side rearview mirror that is so deceptive that a warning that “objects in mirror are closer than they appear” is on it. Have you ever had to merge to the right using it? If that mirror is so great, why aren’t all three rearview mirrors of this type?— P.Y., Poquoson, VirginiaA: That mirror is for your safety. The right side of the vehicle has a much greater blind spot than the left. The convex mirror is designed to give the driver a wider view than can be provided by a flat mirror. Many motorcycles have convex mirrors on both sides because there is no center-mounted rearview mirror and together the left and right mirrors cover most of the area behind the bike.
Auto Q&A: The magic of rain-sensing wipers, explained
By Brad Bergholdt, Tribune News ServiceQ: How do rain-sensing wipers work? I love mine — it’s like magic!— SusanA: In most of these systems, a rain sensor is located on the inside the windshield behind the rear view mirror. Infrared light is projected outward through the windshield glass at a 45 degree angle. Depending on how much light reflects back to the sensor (rain, snow or dirt scatters the light, reducing reflect-back), the wipers are turned on at an appropriate speed and delay frequency. Vehicle speed is often another input for automatic wiper operation.Q: I have a 2018 GMC Sierra 3500 HD with the 6.6 liter diesel engine and Allison transmission. The truck generally gets quite respectable mileage, using about 10-11 liters of diesel per 100 kilometers (22-23 miles per gallon) on the highway. From time to time, though, the fuel consumption abruptly increases from this to 16-17 liters per 100 kilometers (14-15 miles per gallon) for about 20 minutes and then returns to normal. This is on level roads at the same steady speed and wind conditions. Fuel consumption will even remain at 4-5 liters per 100 kilometers (52 miles per gallon) when coasting downhill where it normally drops to near zero. Why does this occur?— LenA: I believe what you are noticing is the truck is performing an active regeneration procedure, which involves the spraying of additional fuel into the exhaust at certain times to create significant heat so as to burn off accumulated soot (particulate matter) in the diesel particulate filter (DPF).Duramax and other diesel engines built since 2011 employ a sophisticated and sometimes problematic exhaust emissions treatment system including (from front to rear on Duramax): hydrocarbon injector (HCI), diesel oxidation catalyst (DOC), diesel exhaust fluid (DEF) injector, selective catalyst reduction (SCR) catalyst, and diesel particulate filter (DPF). The parts we’ll focus on are the 9th injector (HCI) and the DPF.Your diesel particulate filter traps soot and requires periodic cleaning (oxidation) on a regular basis. A combination of heat added due to fuel being injected (about 1,000-1,300 degrees F/538-704 degrees C) and precious metals within the DPF create this reaction. If the truck is driven on the highway frequently, some soot cleaning occurs naturally (passive regeneration). Active regeneration occurs when the system either senses a level of differential pressure before and after the DPF indicating about 42 grams of soot has built up or 700 miles have accrued since the last active regeneration process. Raw fuel is injected into the exhaust via the HCI to raise exhaust temperature for a period of approximately 20 minutes, as you have noticed on your fuel consumption readout. Other clues active regeneration is occurring are a different exhaust sound, elevated idle speed, an odor, and more noticeable heat beneath the truck as it is stationary.
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