By spinedocab, Fri Jan 23, 2009

Original thread: M30 cooling system bleeding

A reliable way to bleed the cooling system on the M30 ("big six"). The procedure is from Jim Rowe at Metric Mechanic. It also works on the M20, with one filling note below.

Procedure

1. After the repair, before adding coolant, remove the bleeder screw and run a small piece of wire down the hole to dislodge mineral deposits.
2. Put the screw back, but leave the valve open.
3. Open the heater control valve and add coolant until it begins to escape from the bleeder hole.
4. Close the bleeder screw. Put the expansion-tank cap on and tighten it.
5. Disconnect the small coolant hose that runs from the radiator to the expansion tank at the expansion tank. Hold that hose up as high as you can. This is the "small elevated hose" — it is still attached to the radiator.
6. Attach a spare hose to the expansion-tank nipple you just uncovered. Gently blow through that spare hose until coolant comes out of the elevated radiator hose.
7. Remove the blow hose and reconnect the radiator hose to the expansion tank.
8. Top the expansion tank to the full mark.
9. Start the engine, warm it up, and check for leaks.

The spare hose is extra — it is not one of the hoses already on the car. Keep the tank reasonably full and the cap on while you blow.

The bleeder is on top of the thermostat housing: look at the fan, then about 4 inches back toward the engine. 8 mm wrench. (wkohler, photo in the thread)

M20 / a fully drained system

The same method works on M20s. If the system is completely empty, start filling from the radiator end of the top hose so the block fills from the bottom (and fills faster). Blowing into the bottle with the bleeder still open can move the last pockets of air. Try not to ingest antifreeze. (nutgone)

From the discussion

Clarifications of the "blow hose" vs the elevated radiator hose are from spinedocab's later reply in the same thread. M20 filling note from nutgone. Bleeder location from wkohler via Fuel.