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  1. #1
    Trale
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    Always bleed when adding any coolant?

    My coolant level seems to dip a little over time. I have backup bottles of coolant ready to refill the reservoir tank, but I'm wary of air bubbles getting into the system.

    Just how big of a concern is this issue, for example, if I simply dump in half a litter of coolant mix straight into the reservoir without messing with the bleed screw, etc?

    My mechanic gave me a fairly simple instructions no how to add coolant and bleed out air:

    1) Open the cap (car must be cool and have not been running for hours)
    2) loosen the bleed screw
    3) pour in coolant slowly, and notice air bubbling out of bleed screw
    4) When air stops bubbling, tighten the bleed screw
    5) Close the cap.

    But this runs counter to more complicated bleeding procedures I've read that includes turning on the engine and reeving up.

    What's the Best Practice procedure I should follow whenever I need to refill some coolant (not a complete flush).


  2. #2
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    Not required

    If you do not take the cap off the radiator, just add coolant to reservoir to the fill line, there is no reason to mess with anything else. This is assuming the reservoir is merely low, not empty.

  3. #3
    Robert Platt Bell
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    Where is the coolant going?


    That's really your real problem right there. A properly running car should not use any coolant whatsoever.

    I would try to track down the source of the leak. You didn't say what year or model car, as they have different cooling systems.

    On my 2.8's the small hose near the fill cap has a band clamp that tended to leak. I was able to fix this by carefully cutting off the clamp and using a stainless steel (nautical) worm gear clamp.

    My 3.0 uses quick-release hoses (!) which is a slightly different setup.

    Usually, BMW coolant leaves a blueish-white residue, which on a clean engine, shows up clearly.

    The water pump on any car fails over time. The usual failure mode is the seals failing, causing coolant to get into the bearings, which take out the bearings, causing the fan to wobble and throw blades, or the plastic impeller (if so equipped) to hit the inside of the block housing and disintegrate.

    The water pump has a "weep hole" below the shaft, and if any coolant or white residue appears here, it means it has traveled through the bearings and seals.

    I replaced the entire cooling systems on my 2.8's at 70,000 miles. I replaced the water pump on my 3.0 at 100,000 miles (the rad was already replaced after an accident). It is not a bad idea as good preventative maintenance.

    As for bleeding, it depends on how low you are letting the coolant go. The head is the highest point in the system and if the coolant goes low, air in the head will cause it to boil out, warp the head, blow the head gasket, etc.

    For this reason, you should NEVER let a BMW overheat, as it will cause great damage in a short period of time. If it overheats, pull over immediately.

    The boards are full of sob stories in this regard.

    The other problem with continually adding coolant is that you are letting air in the system again and again, which not helpful. The modern cooling system in a BMW is sealed, so once it is charged, no additional air gets in. I would think over time, that this continual refilling is going to add to internal corrosion problems, although that is really not the main concern. You are are higher risk for an overheating incident.

    So I would figure out where the coolant is going first. Carrying a gallon of BMW coolant (mixed with distilled water, 50/50) and continually topping it off, is no long-term solution.

    I'm guessing you have a water pump leak. How many miles on the car?

    Good Luck!

  4. #4
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    Re: Where is the coolant going?

    Thank you for that detailed explanation. I was thinking that the expansion tank was a overflow tank and vented to the atmosphere as on my GM built vehicles. I was aware of the design when I replaced the coolant a year ago, but was not thinking about the possibility that the tank could be emptied and allow air in the system.

  5. #5
    Trale
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    Re: Where is the coolant going?

    Hi Robert, thanks for the detailed response.

    It's puzzling me as well about where the coolant is going. There are no leaks to the ground (easy visual inspection), and I just had my mechanic check the entire cooling system, and did a pressure test on the engine. He was worried that coolant is leaking into the engine, but didn't find any (I even did a complete coolant flush AND oil change a few weeks ago).

    I will monitor the situation and if the coolant continues to gradually dip, I will take more serious measures.

  6. #6
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    Waterpump

    I have had to replace two OEM pumps since I purchased my 2.8 in 98. The first one went around 23K and the secound went around 66K. In both cases mine was loosing coolant like yours. No drops under the car on the ground. Shop said that at high speeds the coolant was leaking at the pump slowly.

  7. #7
    Robert Platt Bell
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    Listen to da man....


    I have replaced these on three of my four BMWs. I've tried cast iron, stainless, and even the fancy expensive Stewart one. But the main thing is the shaft seals. Once they go, all bets are off.

    A cheap replacement is like $38 and it ain't hard to do yourself. Well, for me, anyway....

    Here is one I put on a 3.0 liter engine.... I replaced the serpentine belt, tensioner, and the electronic thermostat as well.

    On the 2.8's you can buy a whole new cooling system for about $500 in parts. It seemed like cheap insurance....

    Good Luck. Odds are, it's leaking at the water pump. Look for traces of blueish-white powder from the BMW coolant.

    You ARE using BMW coolant and distilled water (50/50 mix) and flushing every couple of years, right? If not, find a new mechanic. No green antifreeze in BMWs! (or Yellow, and especially not red!)

    Good Luck!

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