BMW 318/325/M3/525/535/M5 1989-1993 Repair Information




The battery in your vehicle can be mounted in a variety of locations depending on the model, engine or chassis style, convertible or hardtop. The battery is mounted underhood on the right side on the 318is, 325iC and the 525i. The battery is mounted under the rear seat on the 535i and M5. The battery is mounted in the trunk on the right side, under the trunk liner, on the 318i and 325i.

When the battery is mounted under the rear seat cushion, the cushion can be removed by pulling up on the front edge and removing from the vehicle. Be sure that the seat cushion is secure when it is replaced so it doesn't become dislodged in a sudden stop. Be sure the vent tube is not crimped when replacing the cushion.


See Figure 1

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Fig. Fig. 1: Checking the battery with a hydrometer

The original equipment battery installed in your BMW is a maintenance free, non-sealed unit. This means that even though the unit should never need fluid in its useful life, the level can be checked and replenished if severe service made the addition of fluid necessary.

If the car is not driven much, or is used for stop and restart type of driving, the battery may not have an opportunity to be recharged by the alternator. With the high usage of on-board electronics and the associated high electrical load, it is important to keep the battery in a fully charged state. If many short trips are anticipated, that would leave the battery low, either change your route of travel to include some highway driving to allow the battery to charge or use a trickle charger installed in the manner intended by its manufacturer.


Clean the top of the battery before removing the cell caps. With the battery exposed and the cell caps removed, the fluid level should be 0.2 in. (5mm) above the plates or at the level marker visible in the opening, if equipped. Fluid should not need replenishing in general use, but extended periods of hot weather use can lower the level. Fill the cells with distilled water, only. Do not fill the cells with battery acid!

If water is added during freezing weather, the car should be driven several miles to allow the electrolyte and water to mix. Otherwise the battery could freeze.


See Figures 2, 3 and 4

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Fig. Fig. 2: Using a terminal puller to remove a stuck battery terminal

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Fig. Fig. 3: Cleaning the battery post with an inexpensive cleaning tool

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Fig. Fig. 4: Cleaning the battery cable with an inexpensive cleaning tool

Once a year, the battery terminals and the cable clamps should be cleaned. Loosen the clamps and remove the cable, negative cable first. On batteries with posts on top, the use of a puller specially made for that purpose is recommended. These are inexpensive, and available in auto parts stores.

Clean the cable clamps and the battery terminals with a wire brush, until all corrosion, grease, etc. is removed and the metal is shiny. It is especially important to clean the inside of the clamp thoroughly, since a small deposit of foreign material or oxidation will prevent a sound electrical connection and inhibit either starting or charging. Special tools are available for cleaning these parts, one type for conventional batteries and another type for side terminal batteries. Get the type for your battery; all BMW's are equipped with top post batteries.

Before installing the cables, loosen the battery hold-down clamp or strap, remove the battery and check the battery tray. Clear it of any debris, and check it for soundness. Rust should be wire brushed away, and the metal given a coat of anti-rust paint. Replace the battery and tighten the hold-down clamp or strap securely, but be careful not to over tighten, which will crack the battery case.

After the clamps and terminals are clean, reinstall the cables, negative cable last, do not hammer on the clamps to install. Tighten the clamps securely, but do not distort them. Give the clamps and terminals a thin external coat of grease after installation, to retard corrosion. Replace the vent tube, if equipped.

Check the cable at the same time that the terminals are cleaned. If the cable insulation is cracked or broken, or if the ends are frayed, the cable should be replaced with a new cable of the same length and gauge.

Keep flame or sparks away from the battery; it gives off explosive hydrogen gas. Battery electrolyte contains sulfuric acid. If you should splash any on your skin or in your eyes, flush the affected area with plenty of clear water; if it lands in your eyes, get medical help immediately.


At least once a year, check the specific gravity of the battery. It should be between 1.20 and 1.26 at room temperature.

The specific gravity can be checked with the use of a hydrometer, an inexpensive instrument available from many sources, including auto parts stores. The hydrometer has a squeeze bulb at one end and a nozzle at the other. Battery electrolyte is sucked into the hydrometer until the float is lifted from its eat. The specific gravity is then read by noting the position of the float. Generally, if after charging, the specific gravity between any 2 cells varies more than 50 points (0.050), the battery is bad and should be replaced.

It is not possible to check the specific gravity in this manner on sealed ("maintenance free") batteries. Instead, the indicator built into the top of the case must be relied on to display any signs of battery deterioration. If the indicator is dark, the battery can be assumed to be OK. If the indicator is light, the specific gravity is low, and the battery should be charged or replaced.


The battery on your BMW can be charged without removing the battery from the vehicle. On vehicles with the battery mounted underhood, connect the charging leads directly to the battery posts. On vehicles with the battery mounted in the trunk or under the rear seat cushion, connect the positive charging lead to the remote positive terminal under the hood and the negative lead to the engine lifting bracket.

Never charge a frozen battery! The battery may explode and cause personal harm. Allow the battery to thaw before charging.

Charging must be done with the engine not running and turned OFF. Do not "quick charge" or use a higher voltage than the battery is rated as this can damage the battery and electrical system.


When it becomes necessary to replace the battery, select a battery with a rating equal to or greater than the battery originally installed. Deterioration, embrittlement and just plain aging of the battery cables, starter motor, and associated wires makes the battery's job harder in successive years. The slow increase in electrical resistance over time makes it prudent to install a new battery with an equal or greater capacity than the old one. Never use a battery with less capacity.

When replacing the battery, remove the negative cable first, then the positive. Remove the hold-down strap bolt and remove the battery. Install the battery and tighten the hold-down strap bolt. Connect the positive cable, then the negative. Be sure the vent tube is not blocked or crimped.


See Figure 5

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Fig. Fig. 5: Remote positive battery terminal used for jump starting

Follow the procedure listed in "JUMPSTARTING A DEAD BATTERY" or your owners manual. Be sure that before you disconnect the cables, return the engine speed to idle, turn on the rear defogger, the headlights and the heater fan to help absorb the voltage spike that can occur during disconnection. This will help prevent possible damage to the electrical system.


Belts should be inspected for both tension and condition at intervals of 12,500 miles (20,000 km) and shortly after replacement. Belt tension is checked by applying pressure (about 10-15 lbs.) with your thumb midway between 2 pulleys. The belt should deflect (stretch) about 1 / 2 - 3 / 4 inches for each 10 inches of distance between pulley centers. The belt should spring tight, not sagging or having play, but not so tight that it requires tremendous effort to get a slight deflection. Excessive belt tension may wear the bearings of the accessory being driven, or may stretch and crack the belt, while insufficient tension will cause slippage and glazing.

Inspect the belt for separation between the outer surface and the Vee, and for radial cracks, which usually begin at the inner surface. The driving surfaces should be rough, slightly cross-hatched because they are fabric covered. If the surface is perfectly smooth, the belt has slipped, and this has caused overheating. A glazed belt cannot offer a sufficient amount of friction to carry the load without excessive tension. Belts which show cracks or glazing should be replaced.



See Figure 6

  1. Replace belts with the proper part. A belt of the wrong length will have to be pried on if too short, a procedure that will seriously damage the belt even before it turns around once, or which may prevent sufficient tightening to compensate for wear long before the belt has really worn out. If you must use a belt that is just a little too short, you might be able to avoid stretching it during installation by completely dismounting the driven accessory, working the belt around the pulleys, and then remounting the accessory.
  3. Replace the multiple belts in sets only, as work belts stretch and mixing stretched belts with new ones will prevent even division of the load.
  5. Do not attempt to change belt tension or rotate an accessory for belt replacement without loosening both the adjustment bolt (the bolt which runs in a slotted bracket) and the pivot bolt.
  7. Most of the accessories come equipped with toothed bolt adjusters that avoid having to pry on the accessory to tension the belt. If the accessory is not equipped with a toothed bolt adjuster, pay heed to the following: Do not pry the driven accessory with a heavy metal bar if you can get sufficient belt tension by hand. This applies especially to aluminum castings or air/fluid pumps, where distortion of the housing can be a critical problem. If you must pry, pry on a substantial steel bracket only or, failing that, on the part of the casting the adjusting bolt screws into. Some accessory mounting brackets are designed with a slot or square hole into which you can insert a socket drive for tensioning purposes.

To replace a belt, first locate the pivot bolt. This holds the unit to the engine block or to a short bracket which has only a hole-no slot. If the pivot bolt does not use a nut welded onto the back of the accessory or a bracket you will have to apply wrenches at both ends-to both the bolt and nut to loosen this bolt. Loosen the bolt slightly-don't release all tension, as you will want the accessory to stay securely mounted to get an accurate tension adjustment later.

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Fig. Fig. 6: Adjuster bolt on the alternator-E36 318i shown

Loosen the adjusting bolt. This passes through a long slot in a bracket and usually runs right into threads cut into the main body of the accessory. Now, all belt tension will be gone.

Move the accessory all the way toward the engine, and pull off the belt. Position the new belt around all the pulleys. Make sure it tracks in all the pulley grooves and, if there are multiple pulleys or pulleys and belts involved, make sure the belt runs in pulleys which are directly in line with one another.

Be ready to tighten the adjusting bolt. Pull or pry the accessory away from the engine until the tension is correct (see above), and then tighten the adjusting bolt. Finally, tighten the pivot bolt. If the accessory is equipped with a toothed adjusting bolt, rotate the bolt with a wrench to obtain the adjustment. No prying will be required.

When installing a new belt (one run less than 10 minutes) put a little extra tension on it to allow for stretch and seating in the pulley Vees during break-in. About 30-40 percent extra tension will do. Instead of deflecting as much as3/4inch, the belt should deflect a little less than1/2inches for each 10 inches of distance between the pulley centers. Recheck tension of new belts several days after installation in case of stretch.

Multi-Vee Type

See Figures 7 and 8

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Fig. Fig. 7: Belt routing on E36 325i with M50 engine

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Fig. Fig. 8: Removing tension from the belt tensioner roller

  1. Before removing the belt, take note of the routing of the belt over the pulleys. If there is not a diagram on an underhood sticker, draw a diagram of the routing. This will be of great help when replacing the belt.
  3. Remove the pulley covers, if equipped and insert a hex key in the tensioner pulley. Rotate the pulley clockwise to release the tension in the belt.
  5. Remove the belt from the pulleys.
  7. When replacing the belt, be sure that the belt is fully seated in the grooves and it is in the proper routing arrangement.
  9. Release the tensioning pulley.

Worn hoses will feel brittle, the lower hose may be permanently narrowed at one point from suction, or may appear frayed or cracked. New hoses will be springy and pliable yet firm, the rubber surface will be solid and smooth, and there will be no evidence of string reinforcements showing through.


  1. Remove the splash guard from under the vehicle. Put a bucket of about 2 gallons capacity under the radiator drain. Remove the drain plug.

When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal even in small quantities. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old. Coolant can be recycled at shops equipped with coolant recycling equipment

  1. If a heater hose is being replaced, turn the rotary heater control to "Warm" and allow any water contained in the heater core and hoses to drain.
  3. Loosen the clamps at both ends of the hoses. Work the hose ends off the radiator or heater core and engine block connections.
  5. Install the new hose in reverse order. If the hose has bends molded into it, make sure to position the hose so that it does not become crimped at these points. Also, install new factory style hose clamps onto the hose from both ends before sliding hose ends onto connections. Position the clamps so they are accessible once the hose is installed. Make sure hoses slide all the way onto the connectors. Make sure you then slide the clamps over the lips on the connectors but not all the way at the ends of the hoses.
  7. Tighten the clamps securely, and then refill the cooling system.