Manual - Chapter 4 - Cooling

7. Hoses and connections: removal, refitting and checking for leaks

  1. The radiator is connected to the engine unit by three flexible hoses, there being an additional hose between the coolant pipe stub and the thermostat housing. The hoses should be inspected periodically and renewed if any sign of cracking or perishing is discovered. The most likely area for this is around the clips which secure each hose to its unions. Particular attention should be given if regular topping up has become necessary. The cooling system can be considered to be a semi-sealed arrangement, the only normal coolant loss being minute amounts through evaporation in the expansion tank. If significant quantities have vanished, it must be leaking at some point and the source of the leak should be investigated promptly.
  2. To disconnect the hoses, use a screwdriver to slacken the clamps then slide them along the hose clear of the union spigot. Carefully work the hose off its spigots, noting that it may be necessary to slacken, or remove fully, the radiator mounting bolt to provide room to manoeuvre. The hoses can be worked off with relative ease when new, or when hot; do not. however attempt to disconnect the system when it is hot as there is a high risk of personal injury through contact with hot components or coolant.
  3. Warning: the radiator hose unions are fragile; do not use excessive force when attempting to remove the hoses. If a hose proves stubborn, try to release it by rotating it on its unions before attempting to work it off. If all else fails, cut the hose with a sharp knife then slit it at each union so that it can be peeled off in two pieces. While expensive, this is preferable to buying a new radiator.
  4. Serious leakage will be self-evident, though slight leakage can be more difficult to spot. It is likely that the leak will only be apparent when the engine is running and the system is under pressure, and even then the rate of escape may be such that the hot coolant evaporates as soon as it reaches the atmosphere, although traces of antifreeze should reveal the source of the leak in most cases. If not, it will be necessary to use testing equipment, as described in the previous Section, to pressurise the cooling system when cold, thereby enabling the source of the leak to be pinpointed. To this end it is best to entrust this work to an authorised BMW dealer who will have access to the necessary equipment.
  5. In very rare cases the leak may be due to a broken head gasket in which case the coolant may be drawn into the engine and expelled as vapour in the exhaust gases. If this proves to be the case it will be necessary to remove the cylinder head for investigation.
  6. Other possible sources of leakage are the 0-rings sealing the water pump body/crankcase joint or the joint between the crankcase upper and lower sections, the mechanical seal and the 0-ring sealing the coolant stub union. All these should be investigated and any leaks rectified by tightening the retaining screws, where applicable, or by renewing any seals which are worn or damaged.
  7. On refitting hoses, first slide the clamps on to the hose and then work it on to its respective spigots. Do not use lubricant of any type; the hose can be softened by soaking it in boiling water before refitting, although care is obviously required to prevent the risk of personal injury when doing this. When the hose is fitted, rotate it to settle it on its spigots and check that the two components being joined are securely fastened so that the hose is correctly fitted before its clamps are slid into position and tightened securely

7.2 Hoses are secured by screw-typed clamps at each end

7.6 Do not forget coolant stub O-rings when looking for leaks