ACtion Magazine - May 2014 - (Page 31)

Volkswagen mapped cooling system By Jacques Gordon just like other thermostats, but this one is electrically heated by pulsewidth-modulated voltage. In some models, the thermostat has two valve discs to control f low through two different coolant circuits. Some models with this thermostat also have an auxiliary radiator with its own electric pump, maybe a check valve or two, and sometimes a separate circuit with an electric pump for the car's heater and/or transmission cooler. The V6 TDI diesel engine actually has separate coolant circuits for the block and cylinder heads so they can operate at different temperatures. The thermostat is mounted in the Coolant Distributor Housing. It bolts directly to the cylinder head and has upper level (outlet) and lower (inlet) level passages, a dual-circuit coolant temperature sensor (G62) and up to 7 hose connections. There's a second temperature sensor (G83) in the radiator, and the PCM (J631) uses both Volkswagen Newer Volkswagen and Audi engines have some of the industry's most complicated cooling systems. All modern cooling systems have two circuits; a main circuit that includes the water pump and engine castings, an additional circuit that includes the radiator; and a thermostat that allows coolant to f low through both circuits when it reaches a pre-set operating temperature. However, VW/Audi cooling systems have an electricallyoperated thermostat that works like a throttle: it can be partially closed even when the engine is fully warmed up. The Powertrain Control Module (PCM) operates the thermostat to adjust coolant temperature according to engine load. Volkswagen calls this "electronically mapped engine cooling," and they use it to increase coolant temperature during part load to reduce emissions. Volkswagen's electric thermostat (F265) has an expanding-wax pellet Volkswagen's coolant distributor housing (left) signals to operate the radiator fan. Many models have an auxiliary electric coolant pump (V51) that runs after the engine is shut down. First introduced on the 1985 Audi 5000T, the after-run pump was originally used to cool the turbocharger housing after the engine is turned off to prevent oil coking in the bearing. The after-run pump is still used today, but it may also be used to increase coolant f low to the heater core under certain operating conditions, and there may also be a valve (N279) to control coolant f low through this circuit. Because the PCM can vary the coolant temperature by as much as 77˚F (25˚C), manual HVAC systems have an electronic temperature control knob (G267), and the control unit operates a vacuum-actuated f low control valve (N147). The same coolant circuit also heats the throttle body. The default or failure mode for the moving parts in the system will provide minimum coolant temperature. While this will prevent the engine from overheating, it will also increase emissions, so cooling system failures will illuminate the Malfunction Indicator Lamp (MIL). In addition to the generic fault code (P0128) associated with cooling system performance, you may also see enhanced codes such as P2181, P1292 or P1296, or Volkswagen codes 18613 or 008577 that indicate failure of specific components. As fuel mileage and emissions regulations tighten, other manufacturers are also developing their own cooling systems that allow coolant temperature to be adjusted rather than just limited. Troubleshooting these systems may be easier for techs who know how to use an oscilloscope. ❆ May 2014 * ACtion 31

Table of Contents for the Digital Edition of ACtion Magazine - May 2014

Selling the right things
Season opener
Freeze Frame
Leonard's Law
Service Port
Virtual View
Last Watch
Member Profile
By the Numbers
Cooling Corner
Industry News
Association News
Letter to the editor
New Products

ACtion Magazine - May 2014