expansion tank replacement

[schnell944]

Hi all,

It's been a while, but I'm back.

So my coolant expansion tank on my '90 535i cracked where it connects to the rubber hose. It's a pretty big crack, and I can't even limp the car to the shop I would take it to. Rather than having the car towed and missing part of my work day, I'd like to fix it myself. My question is, can the expansion tank be replaced without having to flush the whole cooling system of fluid? : just drain the tank, plug the hose, put a new tank on, fill the tank back up. It sounds logical, but in my experience, easy repairs dont always turn out to be so easy.

The reason I ask if this can be done is because I live in an apartment complex, and they aren't very friendly to people working on their cars in the lot (they don't really allow it). And without a garage that I am used to and all the appropriate items on hand (ramps, etc) to carry out a flush, it's just not something I can do I my own.

If it's easy enough to quickly swap the tank myself with minimal drama, I would prefer that.

TIA!

[Kibokojoe]

I took my expansion tank off to clean the pisser line. Put it back on filled the tank and made sure to properly bleed the screw up near the thermostat until all of the air was gone. Ran the car around the block several time to get it warmed up and bleed the screw some more. Worked for me.

[schnell944]

awesome! that's what I thought. when you say "properly" bleed, is there a proper method to this?

[vince]

Replacing the expansion tank isn't difficult, but the o-ring that you can't easily see on the top made it tough to get my old one out.

This is the procedure a friend gave me a while ago, it might be interesting.

vince

Try filling it this way:

Make sure the motor is full through the upper rad hose fitting.
Put the hose back on, open both bleeder screws, fill through the
regular opening. Coolant should start coming out of the screw
on the thermostat housing, close that screw once the coolant
is bubble free. Keep filling until coolant starts coming out
of the radiator screw. (I usually have this screw completely removed
while filling.) Once coolant comes out of that opening, loosely
reinstall the screw. Leave the cap off. Start the car. Coolant
should start coming out of the radiator screw, tighten that when it's
bubble free. Raise the idle a bit (~2K or so), top off while idle
is up, replace the cap. You should've gotten about 2 gallons in
total this way. You should see coolant shoot out of the little
bypass opening in the radiator fill neck when the idle is raised.

You replaced the thermostat, right? If coolant starts bubbling
or pushing out of the fill opening vigourously when you start
it cold, you have bigger problems. Most likely a warped head from
previous overheating. If it still overheats and loses coolant
after all this, it's probably a bad head/head gasket. I assume
it's not leaking anywhere?

[schnell944]

thanks! I'll give it a try.

[2fast]

http://www.bimmernut.com/forum/showthread.php?t=38831

Check out my pics

Was easy to do ,hope all goes well

[Rus]

It sounds like vince is describing the procedure for a 525i that would have two bleeder screws. A 535i only has one bleed screw and the reservoir is not mounted to the radiator but rather to the firewall. A little trick to minimizing the mess during replacement is to use a turkey baster to suck out the coolant from the reservoir. Then you will have minimal loss when you pull the hose off. I did this in about 20 minutes. Easy job and no bleeding required since no air made it down the hose (vertical section below tank keeps fluid in and air out). HTH

[schnell944]

thanks for the help, all. got the new tank on without incident. I have a question though...

the reason that initially got me looking under the hood (beyond the coolant loss from the tank crack) was that the temp gauge was creeping up to 3/4 the other day (stopped in a line at McD's, about 85 deg with ac on). The gauge usually stays dead center. After replacing the tank and lost fluid, the same thing happened again. I got moving again and the needled went back to center from a bit under 3/4ths. I don't think so, but I wonder if I lost enough coolant that some air did get in there.

how should the coolant come out of the bleeder screw on the Tstat? are you supposed to bleed when running? or hot and engine off?

I performed the fan newspaper test, but I've never really understood how to tell if the fan clutch is bad....using a BavAuto magazine I'm able to stop the fan. Not amazingly easily, but I can stop it then easily spin the fan in the opposite direction...

any insight, as always, is greatly appreciated.

*edit* I have posted a separate thread on the possible fan clutch issue**

[Rus]

Sounds like your fan clutch is gone. When it operates properly and actually engages, you will hear a sound similar to a large truck or bus. The fan generates a good bit of noise when spinning fast. When engaged, it should be pretty hard to stop it with paper. Looks like you need to replace that clutch.

Bleeding the system is done while the engine is running. You allow the engine to get up to proper temperature and then open the screw. Spurts of coolant and air will come out until all air is expelled. Coolant will come out if there is no air. Also, turn your heater on full blast to make sure that you are getting air out of all the cooling/heater passages. HTH

[schnell944]

thanks! fan clutch is on its way!