Expansion tank replacement?

[chapmanw]

Hey guys,

I'm having a leak at the bottom of my expansion tank. it appears to be the expansion tank or the gasket that is the cause after doing a pressure test.

Is it a simple task to replace? Appears easy.

I did a quick search and there was no writeup. Any tips for replacement?


thanks in advance,

[fclake]

Hey guys,

I'm having a leak at the bottom of my expansion tank. it appears to be the expansion tank or the gasket that is the cause after doing a pressure test.

Is it a simple task to replace? Appears easy.

I did a quick search and there was no writeup. Any tips for replacement?


thanks in advance,

some come off, some dont, they cost around 40$, have you bled this system before ? you will have to and it can be a bitch so read up on that for sure. I found parking on a steep incline a great tip in the bleeding process. good luck and search for radiator/overeating/bleeding that type of thing.

[shadowpuck]

i just noticed the same problem on our '93 525i. Bentley appears to be silent on the matter - any tips on replacing the expansion tank for either of us?

[DaveVoorhis]

Drain the rad and block, because this is a good time to put in fresh coolant. Unscrew the two screws beside the filler cap above the expansion tank. Remove the plastic cover. Yank out the expansion tank, clean out any gunk, and replace the o-rings. Assembly is the reverse of disassembly. Use antifreeze to lubricate the o-rings on the way back in.

Refilling is straightforward and it's easy to bleed as long as you're not in a big hurry.

Open the bleeder screw on the rad and fill the expansion tank to the brim. The level will slowly drop. When it stops dropping, repeatedly squeeze the rad hoses to expel air. You can feel when you're squishing coolant (good) and not air (bad). Refill the expansion tank to the brim and repeat the above until the level no longer drops.

Now close the bleeder screw, turn the temp dials on the heater to full hot, turn on the blower to 4, and start the engine. Rev it up to 3500 RPM or so three or four times (vroom! vroom! vroom!), then shut off the engine. Don't run it for more than 30 seconds or so. The level will drop in the expansion tank. Open the bleeder screw, refill to the "cold" line, and repeat this paragraph until the level no longer drops.

Drive up and down some hills with the heater on full hot and full blow. Keep an eye on the temp gauge. If it starts to creep over mid-line, STOP THE ENGINE and start over from the top, but be prepared to suspect a stuck thermostat or failed water pump. Otherwise, after driving around for a bit, let the engine cool over night. Then fill to the "cold" line.

Now you're done.

[shadowpuck]

Dave - thank you for the info!!

That's pretty much what I figured would have to happen....

Just curious - the coolant and the rest of the cooling system in this car is fairly new (ie, within the past 4-6 months). In this case, can I just replace the tank itself and then bleed/top coolant as needed - or is a full drain necessary?

[yaofeng]

Can you buy the expansion tank alone? Please tell me where I'd like to get one.

[DaveVoorhis]

You can just drain the radiator.

I assume you can still get the tank from the dealer, if you need it because it's cracked. If not, just get the o-rings.

[shadowpuck]

The tank is available seperately either at the dealer or through various parts suppliers.

Thanks again for the info...

[shadowpuck]

just to follow up.

Myself, along with several local BMW club members tackled this job on our '93 525i today. We also finished an Inspection II (diff fluid, fuel filter, oil change, etc.)

Anyway....

The expansion tank had us defeated for awhile until a moment of inspiration. After you remove the two torx screws at the top of the expansion tank it appears the black plastic piece is still attached to the rest of the radiator. Here's a picture:



Looking at this photo, you'll see the black piece just below the radiator cap and above the newly installed expansion tank. This piece is not attached to the rest of the radiator. It will take some persuasion, but you can pop it out of place and there will be a definite lip to it where it pops off.

Once you get that piece off you can remove the old tank - carefully avoiding the level sensor. Installing the new tank is pretty much reverse of removal (don't you hate that instruction?!), but it is pretty intuitive. We coated the new o-rings with new coolant and then were careful when installing the new tank to not damage the o-rings. We found that a slight tap with a rubber mallet, a small piece of wood, and a rag finished the install of the tank....

We did remove one radiator clip and the plastic rivet for the fan shroud. Removing the clip did make it a bit easier to adjust things and provided some additional access; probably not totally necessary but it helped....

I thought this might be useful info for anyone else planning on replacing their tank (on a M50 motor anyway).