E39 expansion tank

[norseman45]

Hi guys, my first post from here in the UK.

My early (June) '98 523i developed a slight coolant leak recently & I have traced it to seepage from the base of the expansion tank.
I see from OEM that there is a seal at the point where the tank sits in the base, is this likely to be the cause of the leak or would it be advisable to replace the tank itself, together with the cap & all seals?

I need the work to be done by my local garage (shop to you guys?) so as I'm paying for labour I need the problem sorted in one hit.

Thanks all for any advice.

[kallekula]

Buy new

[MtnGn]

New. They are cheap. You will become very adept at changing them out. That and the radiator.

Before I upgraded to Z-ville, all- aluminum, I traveled with tools, coolant, expansion tank and radiator spares in the trunk.

[StephenVA]

Replace the tank, cap, and hoses including the little one hidden on top of the radiator. Replace the rad, belts, WP etc if not done previously

[norseman45]

Many thanks for all the advice, guys.

Would Febi be an acceptable brand name for the tank & what about changing to a reduced pressure cap?
I am retired & don't cover many miles these days, usually no more than 5000 in a year.

[sleuth255]

They're called "explosion bottles" for a reason.. I replace with OEM.

[BimmerBreaker]

Many thanks for all the advice, guys.

Would Febi be an acceptable brand name for the tank & what about changing to a reduced pressure cap?
I am retired & don't cover many miles these days, usually no more than 5000 in a year.

No advantage to a lower pressure cap. The cap does not set the system pressure. It is important that the system not be over-filled so it runs at the correct pressure

[norseman45]

No advantage to a lower pressure cap. The cap does not set the system pressure. It is important that the system not be over-filled so it runs at the correct pressure

Thank you for that, you live & learn to seek second opinions about things you read.
I do always keep the level to the marked line on the bottle.

[CPHES]

Keep it below the marker. I run with the top of the red stick sitting 1 inch below the base of the neck. Leaves more room for thermal expansion. You are talking about a few ounces of coolant difference.

[norseman45]

Keep it below the marker. I run with the top of the red stick sitting 1 inch below the base of the neck. Leaves more room for thermal expansion. You are talking about a few ounces of coolant difference.

Thank you for that advice.

[zaklee]

I have two follow-on questions related to my '98 540i V8:

1. Coolant level 1" below the neck WHEN COLD, correct?
2. I have a small leak where the barbed nipple for the vent hose come out of the top, driver side of the radiator (before it goes across the radiator to the expansion tank). It's clearly NOT from the hose/barb connection. It looks as though that barb is pushed into the top of the radiator - there's a visible seam there and it almost looks like there are two tabs that could be release to pull it out. But I dare not try. I've looked at RealOEM. The diagram there doesn't match my configuration as it shows the nipple coming off the back, not the top. There's no part number, etc. Is it possible that nipple is removable and there's an O-ring in there? Or do I need to replace the whole radiator for this little drip? Ok, that was really three questions.

[sleuth255]

That's right where they break sadly. Mine was part of the radiator and not a separate fitting. New radiator was required for me.

[Dave Sal]

I had a leak at the plastic nipple for the radiator return hose. It has an o-ring that tends to flatten out over time. I got mine out by pulling up and twisting the nipple. I've read that you can remove the coolant hose and reach in with a 10mm socket to squeeze the tabs that hold it in place. Replacing the nipple solved my leak.
nipple removal 1.jpgnipple removal 2.jpg IMG_5305.jpg

[sleuth255]

Wow... Mine is molded in. Probably difference in model years.