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M30 6 Cylinder Engine Coolant System Bleed
There is a lot of discussion about how difficult it is to correctly bleed these straight 6 engines. Some say to raise the front of the car, face it uphill etc… Never on this car has any of that been done. If the system is re-filled and then bled correctly then the following simple procedure will suffice. If you are constantly getting air locks you need to look for other reasons as to why, coolant leaks, pressurisation etc…
This car never uses any water at all, period. The coolant is changed every year rather than two years as stated and only genuine BMW coolant is used. The temperature needle rests a needle’s width below the centre line no matter what,
idling for two hours, stuck in a traffic jam, air con on all day it makes no difference. If the system has no leaks, the pump is good, belts tightened correctly, correct radiator cap, bleed line free, auxiliary fans and switch working, viscous fan operating correctly, you should never have a problem with the cooling system. This car has the added benefit of 100% inert softened water straight from Sizewell B’ plant and no it doesn’t glow in the dark. It advisable once the system is known to be fine to use softened water or “water wetter” additive although if the correct coolant is used it’s not a 100% necessity. The following is based on you knowing you have no water leaks, blocked radiator, failing water pump etc... i.e. you have either overhauled the system or know it to be in operating correctly and are either changing the coolant or topping up after pump change etc…if you know you are loosing coolant from somewhere and just a small top up is required to keep you going it should not be necessary to perform a system bleed. The main, repeat main issue with bleeding this system is the small bore return line from the LH top corner of the radiator back to the expansion tank becoming blocked,
or kinked / damaged. The only way natural bleeding of this system occurs is via air going through this pipe back to the expansion tank as in most other car systems like this. To check your pipe is clear simply disconnect it at the radiator end, remove the radiator cap and blow through it, it shouldn’t be hard to blow, just the resistance felt through it being a small bore pipe. It can become blocked quite commonly at the entrance point inside the expansion tank as well
Diagram showing return line
Original fitment is of crimp clamp, simply replace with standard jubilee type
If you are totally re-filling the system please ensure enough coolant is available for a 50/50 mix with water and that all the hoses and plugs are reconnected, it’s easy to forget one!
M30 Engine coolant capacity is 12.5 litres, you will always have some resident in the heater matrix and generally for this car 4 litres of coolant is purchased therefore 8 litres total approx (50/50) is used to change the system, more if you have changed the radiator, drained the block etc…
When ready to re-fill the system start with ignition on and temp wheels on hot. This should run the auxiliary heater pump ensure coolant in pushed through the heater matrix.
Remove the radiator cap, undo the bleed screw on top of the thermostat housing, undo the small bore return line at the joint from the rubber hose to the plastic hose giving you about six inches loose from the radiator corner, try to keep this hose upright, a screwdriver wedged into the radiator top and hook this pipe around it generally works if you don’t have an assistant. This makes it the highest point to bleed on the system.
Slowly fill the system with correct 50/50 mix of antifreeze and water, keep filling until spillage comes from the thermostat bleed screw and tighten this screw.
Keep filling until coolant comes out of the top of the raised small bore line, this ensures the radiator is basically full. Re-connect the line. Make sure the coolant level is correct on the expansion tank; leave it a couple of minutes to settle.
This car is always started up with the expansion tank cap off allowing you to check that coolant is circulating by seeing a small stream of coolant coming out of the small bore return line into the expansion tank, if so everything is fine. Re-fit the cap, job done!

Bleeding the Coolant, m30