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Use the Tech Tips links below to learn some interesting tips, shortcuts, or special things to watch out for when owning and servicing your BMW automobile. Simple advice from our experts that you can use to take better care of your BMW. Check back often as this page is being updated frequently! 

Sludge Monster
Safely Jump Starting your BMW
BMW Model Codes
BMW Engine Codes
Heel/Toe Downshift

We've all probably seen an engine that's been consumed by the "sludge monster". It's not a pretty sight and has been the cause of death of many engines. The first clue that an engine has been inhabited by the sludge monster usually becomes evident during an oil change (when the thick goo dribbles out the oil pan drain hole or nothing at all comes out). We usually identify the fatal cases of sludge monster victims after the vehicle arrives at the shop under the auxiliary power of a tow truck.

Contaminants are deadly enemies of an engine. They enter with the air flow and are also generated by the friction of metal against metal. These facts may astound you: for every 100 gallons of gasoline burned in an engine, the following by-products are produced:

     90 to 120 gallons of water
3 to 10 gallons of unburned gasoline
1/2 to 3 pounds of soot and carbon
1/4 to 1 pound of varnish
1 to 4 pounds of sulfuric and nitric acid

A measurable percentage of these by-products ends up in the motor oil. Detergents and dispersants in the oil must be able to keep most of these con-taminants neutralized or suspended in the oil as microscopic particles so they don't form sludge, damaging deposits and corrosion. When the waste materials are dispersed properly in the oil, the filter can trap the larger particles. During an oil change, the contaminants too small to be filtered are re-moved with the engine oil. It's important to note here that good air filters and good oil filters trap more contaminants than lesser quality filters, making the oil's job easier.

Sludge formation begins when the chemically suspended particles of contaminants begin to settle out of the oil. It's a fairly daunting task for engine oil to suspend all the contaminants thrown at it, and any engine oil can do this successfully to a point. Amsoil, and some other quality synthetic motor oils, are able to perform this task more effectively and for longer periods of time. But eventually, if the oil is not changed often enough, a "breaking point" will be reached. This breaking point is either when there are too many contaminants to handle or when the oil's chemical defenses are weakened, and it is caused by two main things: excessive accumulation of contaminants in the oil and chemical changes in the makeup of the oil itself (depletion of the additives and oxidation).

As more particles are suspended, less of the additives are available to do their job. Knowing this makes it easy to see why too much time between oil changes can be one cause of the oil reaching its "breaking point".

The sludge monster's invitation can be repeatedly rejected. To keep the sludge monster looking for a dinner date in someone else's engine, use a quality fully synthetic oil in recommended viscosity and change it at recommended intervals.

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"Jump starting" should be avoided if possible because of damage that can occur to various electrical components. The electronics found throughout our cars can handle voltages up to 15v but only briefly. Jump starting equipment found on some tow trucks can operate anywhere from 18 to 24 volts. Damage to certain electrical components is assured if this equipment is used.
However, in certain circumstances, jump starting may not be avoidable. To protect the electrical components in your car, follow the procedure described below. 

  • Make sure that neither of the vehicles involved are touching (on certain vehicles, ground points may exist on bumpers).
  • Ensure that both vehicles have batteries of the same voltage and are approximately the same size/strength to ensure sufficient power for jump starting.
  • Carefully observing polarity, connect the positive jumper cable to the battery's Positive Junction Post (or battery positive terminal, if the vehicle is not equipped with a battery's Positive Junction Post) of the vehicle to be jumped started and then the battery positive terminal of the vehicle being used to jump start. (See below for picture of Junction Post)
  • Next connect the dead car's negative jumper cable to a CHASSIS GROUND (i.e.. Bolt at front shock absorber upper mount) on both vehicles. At this point, connect the last cable, the negative for the jumping car to a CHASSIS GROUND. Doing so avoids any potential arcing of battery gases, which could cause an explosion.
  • Jump start the dead vehicle by turning the key as usual. For the first attempt, leave the jumping car off.
  • If the car doesn't start on first attempt, start the jumping car and leave it running. Wait a few minutes before the 2nd attempt. If it still will not jump start, odds are your battery is completely dead. In this case, contact us to have your vehicle towed in so we can thoroughly check the charging system and fix the problem.
  • If the dead car successfully starts, before disconnecting the jumper cables, switch on the heater fan to the highest speed, the rear window defroster and your low beam headlights. This helps minimize voltage spikes when disconnecting the cables.
  • Disconnect the negative cable on jumping car first, then the negative on the formerly dead car. Next, disconnect the positive cables in either order. Disconnecting the cables in this order ensures that any momentary arcing that may occur is away from the battery (in the case of vehicles with the battery in the engine compartment) and any gases produced by the battery. To prevent future problems, it is recommended that you schedule an appointment to have your battery load tested and your charging system inspected.  

Failure to follow this procedure exactly may result in expensive damage to your vehicle's sensitive electronics. 

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BMW model codes help you to identify your car in the language that the manufacturer uses (no, not German!). Using the codes lets you order parts and accessories with confidence. For example E39 is a 5-series body from 1996 while E46 is a 3-series body from 98-on.
E Code Model Series Model Years
E3 2500, 2800, Bavaria, 3.0s/si 1968-1977
E6 1600, 1800, 2000 Touring 1973-1975
E9 2500cs, 2800cs, 3.0cs 1965-1975
E10 2002, 2002tii 1968-1975
E10C 2002 Convertible 1971
E10T 2002 Turbo 1973-1975
E12 5 Series 1973-1981
E12/1 5 Series Facelift 1977-1981
E12/1S M Series (M535i) 1980-1981
E20 2002 Turbo 1973-1975
E21 3 Series 1977-1983
E21/1 3 Series Facelift 1978-1979
E21/2 3 Series Facelift 1979-1984
E23 7 Series 1978-1988
E23/1 7 Series Facelift 1979-1982
E23/2 7 Series Facelift 1982-1986
E24 6 Series 1978-1988
E24/2 6 Series Facelift 1988-1989
E24/1S M Series (M635csi) 1984-1987
E24/2S M Series (M6) 1988-1989
E25 Turbo 1972
E26 M1 1979-1981
E28 5 Series 1982-1988
E28S M Series (M5) 1985-1988
E30 3 Series 1984-1992
E30/2 3 Series Coupe 1984-1992
E30/2C 3 Series Convertible 1986-1992
E30/2S M Series (M3) 1987-1991
E30/2SC M Series (M3) Convertible 1988-1991
E30/4 3 Series Sedan 1984-1991
E30/5 3 Series Touring 1998-1992
E30/16 3 Series 4WD (325iX) 1986-1991
E30/88 3 Series Facelift 1998-1991
E30Z Z1 1989-1990
E31 8 Series 1990-1999
E31S 850CSi 1991-1999
E32 7 Series 1988-1994
E32/2 7 Series Longbase 1988-1994
E34 5 Series 1989-1996
E34/5 5 Series Touring 1991-1996
E34/16 5 Series Touring 4WD 1992-1996
E36 3 Series 1992-1999
E36/2 3 Series Coupe 1992-1999
E36/2S M Series (M3) Coupe 1992-1999
E36/2C 3 Series Convertible 1993-2000
E36/2CS M Series (M3) Convertible Unknown
E36/3 3 Series Touring 1996-1999
E36/4 3 Series Sedan 1992-1999
E36/4S M Series (M3) Sedan 1995-1998
E36/5 3 Series Compact 1995-1999
E36/7 Z Series (Z3 Roadster) 1996-2002
E36/7S M Series (M Roadster) 1998-2002
E36/8 Z Series (Z3 Coupe) 1998-2002
E36/8S M Series (M Coupe) 1998-2002
E38 7 Series 1995-2002
E38/2 7 Series Longbase 1995-2002
E38/L7 7 Series Limousine 1999-2002
E39 5 Series 1997-2003
E39S M Series (M5) 1997-2003
E46 3 Series 1999-Current
E46/2 3 Series Coupe 1999-Current
E46/2C 3 Series Convertible 2000-Current
E52 Z Series (Z8) 2000-2002
E53 X Series (X5) 2000-Current
E60 5 Series Sedan 2003-Current
E61 5 Series Touring Not Available
E63 6 Series 2004-Current
E65 7 Series 2002-Current
E66 7 Series 2002-Current
E83 X Series (X3) Not Available
E85 Z Series (Z4) 2002-Current

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Ever wonder what engine code your BMW uses?  These are the current codes used.

BMW Engine Codes

Engine Code Cylinders Engine Size Applications
M10 4 2 Valve 1.6, 1.8, 2.0 Liter 1600, 2002, 320i, 318i
M20 I-6 2 Valve 2.0, 2.3, 2.5, 2.7 liter 323i, 325e, 325i, 528e
M21 I-6 Turbocharged Diesel 524td
M30 I-6 2 Valve 2.8, 3.0, 3.3, 3.5 liter 528i thru 81 630csi,633csi,635csi, 533i,535i thru 92, 733i,735i thru 92
M42 4 4 Valve 1.8 liter 318i/is 90 thru 95
M44 4 4 Valve 1.9 liter 318i 96 on, Z3 1.9
M50 I-6 4 Valve 2.5 liter 325i 92-95, 525i 91-95
M52 I-6 4 Valve 2.5, 2.8 liter 325i 96-99
328i 96-99
M52TU I-6 4 Valve 2.5, 2.8 liter 323i 99-00
328i 99-00
M54TU I-6 4 Valve 2.5, 3.0 liter 325, 330 01+
M60 V8 4 Valve 3.0, 4.0 liter 530i,540i 93-95 740i 93-95
M62 V8 4 Valve 4.4 liter 740i 95-99, 540i 97+
M70 V12 2 Valve 750il, 850i
N62 V8 4 Valve 745i 02
N73 V12 4 Valve 760i 02
S14 4 4 Valve 2.3, 2.5 liter M3 88-91
S38 I-6 4 Valve 3.6, 3.8 liter M5, M6
S50 I-6 4 Valve 3.0 liter M3 95
S52 I-6 4 Valve 3.2 liter M3 96- 99
S54 I-6 4 Valve 3.2 liter M3 01+
M Roadster 01+
M Coupe 01+
S62 V8 4 Valve 5 liter M5 00+
Z8 00-02

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The heel-toe downshift is a fundamental technique to driving fast through corners. During a heel-toe downshift, you'll be steering with the left hand, shifting with the right hand, clutching with the left foot, and working both the brake and gas pedals with the right foot -- all at exactly the same time.


The downshift begins with a full throttle acceleration towards a corner.


Lift the right foot from the gas pedal and press the brake pedal.



Just before the braking is done, the left foot depresses the clutch pedal.

The right hand begins the downshift.

The right foot is still applying, but easing up on the brake pressure as the car approaches the turn-in, then the foot rotates so the heel is above the corner of the gas pedal.

As the shift passes through neutral, the right heel gives a quick push of the gas pedal to rev the engine quickly (the ball of the foot is still on the brake easing up even more).


The left foot releases the clutch, the right foot rotates off the gas. Done correctly the RPMs generated by the throttle blip above matches the RPMs needed, and as the clutch is released the engine engages smoothly with the current wheel speed. There should be no forward or braking lurch when the clutch is let go.


The right foot completes the braking with a smooth release.


The right foot moves over to the gas pedal to assume the normal position at first only to maintain the pressure needed to sustain the vehicle speed throught the first part of the corner. Then pressure is gradually applied to accelerate out of the turn.

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135 West Central Street, Natick, MA 01760
tel: 508.655.3957 | fax: 508.655.7286 | email:

The term 'BMW' is used as a general descriptor for BMW cars. Its use in no way implies an association with or approval by BMW (GB) Ltd, BMW M GmbH or BMW Ag, the German parent company. The term 'BMW', the BMW logo, the BMW font, ASC+T. DCS, M logo, Servotronic, Steptronic, VANOS, "The Ultimate Driving Machine™" and the distinctive shape of BMW cars are recognized to be trademarks owned by BMW Ag, BMW M GmbH and BMW USA LLC. All other trademarks are acknowledged to be the property of their owners.