Technical Tips

Our Technical Tips

Over the many years that we have been working on BMWs there are some problems that we have repeatedly encountered. We have highlighted a few of these below together with some tips we have found useful. If you have any tips of your own that you would be happy to have published on this page please send them to us.

Corrosion on early 3 Series BMWs (E21 and E30)

Check your early 3-series 1976-91 (E21 and E30) for corrosion. Having dismantled many of these models we found that they were all showing corrosion in the same areas. One of the most common sites for rot is the real wheel arch and sill area. On the 2 door models this is mainly caused by water ingress from the rear side window due to defective window seals. Worn seals on the bottom edges of door glass are also leading to rotten door bottoms, and inefficient top door seals are causing water to run down the leading edge of the door and rot the check strap area.

Wet rear foot wells on 2-door 3 Series BMWs (E30)

The 2-door 3-series 1983-91 (E30) has a particular problem with wet rear foot wells. We have noticed that the retaining fixings for the opening clip have a tendency to move their adjustment over the years. Therefore when it rains the water can penetrate between the sealing rubber and the glass. The solution is to remove the black plastic cover on the rear pillar and with the help of a friend pushing on the outside of the glass take out the slack in the two retaining screws so that the glass is tightly against the rubber. The soap sud test works well, if there is a gap the suds will show up on the inside of the car!

Leaking power sunroofs

All BMW’s with power sunroofs tend to have leak problems in later years. Again the seals are often to blame, but occasionally the drain channels are the culprit. With the sunroof open at the maximum you will see a small hole in each corner of the sunroof aperture. These are connected to drain channels, which take excess water away and vent in the engine bay and at the rear wing area. These drain pipes get blocked with leaves and general dirt and periodically require clearing. A long piece of wire should do the trick. Check that the drains are correctly seated, it has been known for the rear ones to come loose on the E30 and let water into the boot causing electrical and other problems.

Poor running on big 6 L-Jetronic or Motronic engines

Poor running on your big 6 L-Jetronic or Motronic engines? We are increasingly finding that the small injection hoses are developing small cracks due to the exposure to the heat of the engine. These may not be readily visible until manipulated in a good light source. Especially check the breather hoses from the rocker cover, the small hoses under the inlet manifold and the large rubber bellows near the air flow meter. Replace these hoses and see the difference in running and fuel consumption.

Leaking fuel pressure regulators on injector rails

Check the fuel pressure regulator on the end of the injector rail. These quite often fail and leak petrol which not only smells bad inside the vehicle but is a fire hazard and a major cause of poor running.

Uneven response on accelerator pedal

If you have poor response to your acceleration, it may be something as simple as a faulty accelerator pedal. They quite often crack at the back where they attach to the linkage which passes through the bulkhead – this is especially the case with the later 2002’s.

Replacing bulbs on the instrument cluster

When fitting new bulbs to the instrument cluster do ensure that the wattage is correct. Many circuit boards are ruined by owners fitting incorrect bulbs!

Overheating problems caused by faulty fan viscous coupling

If you are experiencing overheating problems then the viscous coupling in the centre of the fan blades may be at fault. This locks up as it rotates to pull more air through the radiator. When they fail the fan just freewheels and the car overheats in traffic. To test if yours is faulty take a long stiff piece of paper and CAREFULLY hold it so that it comes into contact with the fan blades. If the fan stops then the coupling is faulty, if the paper is shredded than the coupling is fine!

Read our cooling white paper