Bleed­ing cool­ing sys­tem

Car Mechanics (UK) - - Help! -

My daugh­ter has a 1999 BMW 318i SE man­ual. I re­cently re­placed the ex­pan­sion cham­ber, but, try as I may, I can­not get the heater to blow hot air. My ef­forts to date in­clude fill­ing the large hose run­ning from the en­gine to the ex­pan­sion cham­ber while the hose was raised above the en­gine and when it was ab­so­lutely full, con­nect­ing it up to the ex­pan­sion cham­ber, run­ning the en­gine and open­ing the bleed screw in the hose to ex­pel air un­til only coolant is com­ing out. I have re­peated this sev­eral times, but all my ef­forts have been with­out suc­cess. Ge­orge Wood­ward The sys­tem should be bled out as com­pletely as pos­si­ble with the en­gine cold and with­out the en­gine run­ning. Very of­ten, at­tempt­ing to open the bleed screw while the en­gine is run­ning can drag in more air.

Once the sys­tem has been bled through as fully as pos­si­ble, then the bleed screw should be tight­ened up and the heater set to its max­i­mum tem­per­a­ture with the heater fan set to slow. The advice from BMW is to then run the en­gine with the coolant cap re­moved and give the en­gine three or four bursts of ac­cel­er­a­tion. They also ad­vise not to run the en­gine for more than 30 sec­onds as once the coolant gets warm it will ex­pand.

Af­ter re­fit­ting the coolant cap, give the ve­hi­cle a run to get the cool­ing sys­tem up to tem­per­a­ture. Hope­fully, at this stage, the heater will be blow­ing warm air, but if this is not the case, al­low the en­gine to cool down be­fore re­mov­ing the coolant cap and re­peat­ing the process.

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