It's Always the Little Things
Clogged Body Drains
By Mike Perkins
Owner - Bavarian Machine Specialties

       An easily preventable problem centers on clogged body drains (the small drains that allow rain and carwash water an escape from the body). Drains in the cowling area, sunroof, and convertible top storage compartment are seldom inspected and without attention they can lead to a major calamity. Those who park outside, especially under trees, beware: leaves and debris are easily trapped in key drainage areas, and if allowed to decompose, will completely clog the drains.

       If you have an E34 (5 series from 1989-1995) and allow the cowling drains (those at the base of the windshield under the hood) to clog, expect soggy front footwell carpets after a hard rain as the water winds it's way through the heater box seal and into the car. If this condition goes undetected your soggy carpets will not only mold, there is a good chance your air condition control unit and wiring will corrode and fail. Imagine a moldy, non-airconditioned car simply due to leaves in the cowling drains.

       Clogged cowling drains result in a different disaster for E36's (3 series from 1992-99). Rather than flood the passenger footwell area, the water instead flows to the area housing the engine management control unit (DME) which, at best, causes a non-start condition until the unit dries (or at worst a totally "fried" DME). Perhaps you or one of your friends have experienced a non-start after running your 3 series through a car wash (check those cowling drains).

       Surprisingly, sunroof drains are notorious for clogs. A clogged sunroof drain leads to soaked headliners and or ruined leather seats. A quick check of the drains leads can be performed by pouring a small cup of water into first one corner, then the other corners of the sunroof channel. If clear, you will see the water pool beneath the car behind both the front and rear wheels. If you find a clogged drain be careful using compressed air to clean the blockage: sunroof vent tubes are pressed-on to plastic tubes that can pop off if the clog is stubborn.

       Clogged drains in the convertible-top storage areas of E36's are also problematic. One customer of ours regularly parks beneath a live oak. After a week out of town (when it rained heavily) he returned to find a thoroughly soaked back seat and two inches of standing water in the footwells. Initially he he thought the convertible top leaked, but upon inspection the culprits were completely clogged drains in the convertible top storage area. As the storage compartment filled with water it overflowed into the backseat and onto the floor.


Air Flow Blockage

       Clogs present a different problem on all E39 (5 series from 96-03), here having to do with air conditioning and engine cooling. These cars tend to trap road debris into the lower air conditioner condenser area. Paper, leaves, and other road debris collect between the auxiliary fan and condenser causing a number of heat dissipation issues. The clogged condenser area creates super heated air that affects radiator cooling, auxiliary fan operation, and eventually air conditioner compressor life. A good cleaning of the condenser once every couple of years will help alleviate these potentially expensive situations.

     Paper, leaves and other road debris cause problems with BMWs from the late 1980s that have an alternator cooling duct (especially those with low inlets). Pop the plastic cover off the back of the alternator some time and you will think some rodent built a nest in your alternator. We have found all manner of paper, twigs, leaves and even cigarette butts crammed into the back of the alternator. The ducting acts to cool the alternator's diode plate and is needed especially on later model cars with higher amperage alternators. Heat build up has become such an issue that BMW engineers have tried water cooling the alternator, as on M62 engines. Unfortunately, in my experience the only time the alternator cooling duct is cleaned is after an alternator failure and the expensive new alternator is installed.

     One final clogging problem for now: as everyone knows, the most efficient way to operate the air conditioning system in the hot, humid, Texas climate is in recirculation mode. However, be aware that on all E38 and E39 models (7 series from 1995-2001 and 5 series from 1996-2003) this can lead to a clogging problem with the integrated heating and air conditioning system (IHKA) internal recirculation filters. These IHKA filters are not to be confused with the external air microfilters (which should be replaced at regular intervals as part of routine service). When the IHKA filters become clogged, they impede air flow through the air conditioning system including the blower motor and final stage. If no attention is paid to the IHKA filters, the result will be a 12 hour job to remove the dash and replace a burnt out blower - all for the sake of two small filters. When you replace these original filters for the first time, especially if you have a pet that travels in the car, wear a mask and gloves because it won't be pretty. You won't believe what you've been breathing.

-originally published in the BMW CCA Houston Chapter Newsletter
Summer 2004










Terry Sayther Automotive �MMIV. This page was last modified on  June 24, 2005 8:12 AM   Questions?  Email eags
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