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Coolant System Bubble Removal Procedure

Hi I have a quick question. I have to use specially formulated BMW coolant (the blue stuff, I think ammonia nitrate free or something like that?) for my 2002 BMW 330 Ci. In the instructions on the coolant bottle it says after adding coolant you have to run the car with the overflow reservoir cap off and the heat blasting at full until the car reaches normal operating temperature to remove bubbles from the coolant system. This prevents later overheating. My friend said I don’t need to do this unless I open the coolant system up. What’s the verdict? Is it necessary or unnecessary when just adding coolant to the system? Thanks!

When all else fails follow the directions.


Also, as they appear in the coolant reservoir you have to pop the bubbles or else they will circulate back into the system. I think BMW makes a special tool for this, kind of expensive, but well worth it. :rofl: :joy::joy:

But seriously the air bubbles need to be purged out. Don’t listen to that friend. Can he afford to buy you a new engine, when yours overheats and destroys itself?


Your question is pretty vague. Are you just adding some coolant? A lot?

Or did you do some work on the car that required you to drain the coolant and now you want to refill?

In the first instance, if you are only adding a quart, no bleed. A half gallon? Yes you should bleed.

In the 2nd instance, you should bleed.

This friend , is he a BMW mechanic ? It is easy to give advice when it is not your money at risk. Of course the directions are on the bottle for a reason are they not .

Your friend is right.

If you’re not opening the cooling system up, such as replacing the radiator or water pump, then just add coolant as needed and drive on.

And if air does get into the cooling system, the first thing you’ll notice is little or no heat from the vents.


Thanks guys… just adding a little coolant to top it off since I’ve been losing some very gradually. Also I’ve talked two mechanics and one said do the procedure one said don’t lol. I will probably end up just doing it to be safe.

Hi, I am a BMW technician and yes you do need to bleed them , because of the slanted nature of the M52/M54 they suffer from cavitation in the cylinder head. If you fill the system, leave the cap off and repeatedly squeeze the top hose you should see most of the air come out of the header tank, the carry on as you described. Wouldn’t be the first to damage the head/ head gasket if you don’t.

If you are just topping it off with a cup or so of water, there is no need to bleed it. When you do need to bleed it (and you will someday), There is a bleed screw next to the cap on the overflow tank. Remove that screw with a big flat blade screwdriver or a coin. I take a piece of nylon hose that fits tight in the bleed screw hole and twist it into the hole, then put the other end of the hose into the fill hole in the reservoir. Start car, heater on full hot, and warm it up. You will see the bubbles move from the upper radiator hose through the nylon hose.
I run the front wheels up on ramps to make the front of the car the highest point, but I don’t know if the ramps do any good.
Loosing a cup or so a year is normal. Loosing a cup or more a month means you have a leak. Watch the temperature sensor on the lower radiator hose, its O-ring tends to fail. If you cannot see the source of the leak, it may be the water pump, which is well hidden from sight.

Additional notes: BMW coolant is non-phosphate, non-nitrate, non-silicate coolant (and still it can plug up the heater core eventually). I have read that it is made by BASF, and they don’t seem to sell it by any other brand name in the US. You can use regular anti-freeze in your BMW so long as you don’t use organic acid (AKA “Dex Cool” long life) antifreeze. The seals in German cooling systems do not like that stuff.