Auto Service Professional

OCT 2018

Magazine for the auto service professional

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Page 49 of 69

48 A S P O c t o b e r 2 018 T u r b o S e r v i c e T i p s Circle 120 on Reader Service Card ing soaks into the turbo center housing, raising temperature that can result in oil coking. Some turbos feature water-cooled center housing, which uses engine coolant to act as heat sink. Water lines use a thermal siphon effect to reduce heat. Wastegate Located on the exhaust side of the turbo, a wa- stegate controls boost pressure. Note that some commercial diesel applications don't us a waste- gate, featuring a "free floating" turbocharger. For gasoline engines, there are two types of wastegates: internal and external. Each type al- lows bypass of exhaust flow from the turbine wheel to limit boost pressure to the design level. Internal wastegates are built into the turbine housing, featuring a flapper valve, pneumatic ac- tuator, crank arm and rod end. An external wastegate is located on the ex- haust manifold. e advantage of an external wastegate is that the bypassed exhaust flow can be reintroduced into the exhaust stream further downstream of the turbine, which tends to im- prove turbine performance. Wastegates are featured in many systems in order to control boost to prevent over-boosting. However, some newer designs such as VGT tur- An air charger (intercooler) is used to cool the charge to create greater air density. When replacing a damaged turbocharger, be sure to inspect the entire air circuit, including the air charge cooler (intercooler). If sludge or metal debris has entered the system, the intercooler must be replaced, as it's next to impossible to clean out the tubes in the cooler. If the vehicle is equipped with an external intercooler, even if the cooler has not been contaminated internally, the cooling fins may become contaminated with road debris. Just as you would clean the fins on a radiator or A/C condenser, check to make sure there is adequate airflow through the cooler.

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