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Replace just expansion tank or do cooling system overhaul?

Discussion in 'E85 Z4 (2002-2008)' started by VaBchZ4, Feb 9, 2015.

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    I purchased a mint 2003 Z4 2.5i with 102,000 miles from a dealer about a month ago. This weekend it began leaking a few ounces of coolant. I put the car on ramps and determined that there is a pinhole leak about half way up the left side of the expansion tank. There is no leakage anywhere else. I have heard and read that around 69,000 miles or so, it's best to do a cooling system overhaul and replace all hoses, lines, radiator, expansion tank, thermostat, water pump, etc. as a preventative measure since sudden coolant loss could be disastrous. I have no way of knowing whether this has been done at some point in the past, so I'm putting it out to the experts on this forum. What things are most important to replace if that's the consensus? I plan to do the repairs myself.
    Thanks everyone!
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    eblue540 Fourth Gen Bimmers

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    I cannot speak for the Z4 per se, but I have done exactly what you describe on my e46 325, my e39 540 and and about to do the same to my recently purchased e36/7 Z3 M Coupe which has 80k miles and also has a slow leak. I will be replacing the OEM with an all aluminum Zionsville radiator and expansion tank.
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    Nice ride.

    I chased a "check coolant level" light on my 2002 540i for two years. Replaced the sensor twice, then the expansion tank. A few weeks after I replaced the expansion tank the radiator sprung a leak at a not particularly good time.
    If your car still has the original radiator, I would encourage you to go ahead and replace it with the tank.
    Better to do it on your schedule rather than when it decides to let go.
    The Zionsville radiators are great, just kinda pricey. The OEM replacement radiators will last you another 60,000+ miles and cost about half.

    The water pumps have plastic impellers and if/when they fail, it can be problematic (inconvenient and/or expensive). Just like above, when do you want to replace it? In your garage with a cup of coffee and soft music playing in the background -or- along the side of the road somewhere.

    Enjoy your great new ride.
    Spring is just around the corner.
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    With 100k & unknown maintenance history, & plans for long-term ownership, I'd go for the comprehensive approach - Yes, the Zionsville radiators are pricey, but it should also outlive several o.e. radiators. I'd do an EMP/Stewart water pump, new expansion tank, etc.

    Here's Turner Motorsports pkg. - stock radiator; useful for parts reference also.

    EMP/Stewart water pump info:


    If it's a manual, a trans-fluid drain-&-refill probably wouldn't be a bad idea, same for the diff. If it's an auto, a trans flush on one that possibly never has been flushed runs the risk of loosening sludge & what not & killing the trans, so opting for that is kind of like poking at a hibernating bear; if you leave it alone, maybe you don't have any problem.

    Redline MTL is good for manuals (generally), doublecheck it's the right viscosity spec -

    Diff fluid (again, confirm your specs) -

    Do some googling to see if there's any history of fan blade failure w/ Z4's, there have been other bimmers that suffered fan blade problems - if you have things that far apart, that would be an easy time to swap in a new one if desired.
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    I would recommend doing the cooling system over haul if possible. Takes your mind of one of the weak points of that engine.
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    Thanks everyone!...for the advice and resource links! I agree...bite the bullet now and prevent potential breakdowns and damage later! It's killing me to see it up on ramps, :( so I'm ordering parts to get 'r done!
    P.S. It's the manual 5 spd tranny and I plan the change the trans and diff fluids.

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