losing coolant water

[darren21]

ive got 316ti 2002 and im losing alot off coolant, no leaks , headgasket is fine , any ideas?

[Manolito]

Most common leak on an e46 is the water temperature sensor in the lower radiator hose. The O-ring shrinks and hardens over the years. Pull the electrical plug off the sensor and see if there are signs of coolant round the sensor.

The O-ring is metric sized and not available as a single part in the US. We have to buy the whole sensor to get a new O-ring. Next time I have one leaking, I intend to try wrapping teflon tape around the sensor to see if that will seal it.

The next most common failure is the water pump. If the lower front of your engine is damp with coolant and the source is not apparent, the weep hole in the bottom of the water pump is a good bet. Water pumps tend to last about 150k miles. Is yours approaching that age?

Examine the radiator from beneath. If it is the original radiator, at nine years of age it is about due to fail. The usual failure point is the top hose nipple. Radiators can also fail at the seals between the aluminum core and the plastic end caps, particularly if someone has put organic acid 'long life' coolant in them.

[TerryH]

Dont forget the radiator expansion tank. They crack and the water mists which makes it hard to spot.