Coolant expansion tank explosion

[acarrera79]

In the process of parking yesterday I heard a loud "pop" and coolant started to billow out of the hood. My expansion tank ruptured right in the same spot that I saw in another thread when I did a search. I was driving in an urban area looking for a parking spot, and I have absolutely no idea if I overheated it or not (it's been running fine for the less than two WEEKs that I've had it). Other than all of the coolant system stuff (t-stat, w pump, belts) should I be thinking about anything else? The car has 96k, and I believe it was cpo'd at around 75k. Having an old Saab and an Acura Legend, I always have head gasket failure repeating in the back of my head. Thanks in advance guys, this car is making me sick to my stomach!!! (someone hit it in a parking lot last weekend.)

Should I get the OEM expansion tank, or is the MTC one OK?

[JB740]

if you heard the tank pop and then stopped within a few min of it happening, I doubt you over heated.

[acarrera79]

thank you for saying that... I was trying to parallel park when it happened. I stoped the engine immediately.

[parabellum]

You are fine....there is no way that was enough time to damage your engine. Now...if you went that long with no oil pressure, it might be a different story.

Water pump, hoses, expansion tank (obviously), tstat...and you are good to go.

[graywolf316]

hmmm wierd normaly that would mean a crack in the head, the pressure build up from the air leaking through the cracked head would vent up into the radiator causing a build in pressure and would leak coolant and possibly cause the pop u heard but if u didnt over heat the engine it could just be the person who had it before u had the coolant flushed and didnt properly have the system bled....try bleeding it by loosing the bleed valve and holding the rpm's at around 1,500 untill it stops leting air out then toping of the coolant...see if that works

[parabellum]

No crack in the head is necessary...our expansion tanks are crap...they fatigue and stiffen over time and POW.

The water pump, exp tank, and hoses are like brakes...wear items that should be replaced at regular intervals.

I plan on doing all of the above at 80K as a preventative measure.

[LeftCoastBias]

i was JUST posting in another thread about how the coolant systems in bmw's STILL suck and have to be replaced around 60-70k.

i wonder when (if) bmw will ever fix this weakpoint...

[acarrera79]

Fantastic guys. You've made me feel much better. In addition to the above listed parts, would you suggest a new rad too? I was probably going to throw on in there if it's suggested.

[White94RX]

just replace what's broken. expansion tanks crack all the time.

[01silber]

I would stick with the oem one. They are about 65.00 bucks

[kwikt]

I just replaced my expansion tank last week at 67000 miles. Simple fix.

[dello]

The same thing happen to me about two weeks ago, no big problem. Just replace the expansion tank-my mechanic told me these things happen all the time.

[acarrera79]

Does the new expansion tank come with the float for determining fill level? Mine was lost out of the bottom when the thing went.

[dello]

Yes

[ImportFanatic]

Does the new expansion tank come with the float for determining fill level? Mine was lost out of the bottom when the thing went.

Yes, it's a time consuming swap, but it's easy.

[aarons6]

just make sure when you get done when filling it up you open that little screw that goes in the top and keep filling it untill coolant comes out.

[beamer boy]

Remember when you are re-filling the tank with your water and coolant mixture to turn your heaters all the way up to the hottest point. This opens all the valves in the heating system and lets the mixture flow right around the system so as you do not get any air locks (which could cause your tank to blow again).

[acarrera79]

The only thing I'm thinking about is the T-stat. Every other car I've done cooling system work on has a bleeder screw near the t stat. I guess I'll just follow the bentley. I'm sure that I'll get it right that way.

Do I need BMW coolant, or can I go with the Prestone works with everything extended life coolant.

[White94RX]

the hot water valves are sprung open, powered closed, so if the key is off, the valves are open.

[Bubba68]

My tank split completely in 2 right at the seam at 106,000miles could it just been cuz of a bad tank? I did not over heat prior to it popin.

[nathancarter]

My tank split completely in 2 right at the seam at 106,000miles could it just been cuz of a bad tank? I did not over heat prior to it popin.

They're all bad tanks. 106k miles is right about on target for a rupture.

I generally recommend replacing at around 75k miles, so you can do it on your own schedule, instead of waiting for it to pop on its own time: when you're late for a date, or driving across the desert, or right in the middle of the bad part of town.

[ith5005]

My expansion tank developed a small leak and then turned into a very large leak in a matter of minutes. I just filled mine up with water and drove home 10 miles or so (low coolant light did not turn on and my temp gauge never went up either). The problem you may have is your alternator may go bad. The problem I had was the water and coolant from the tank when it burst got onto the alternator and shorted it (why they put the alternator where they did when they know the tank is garage idk). So I had to put a new alternator in. It is very easy to do just another problem I had with mine. The problem mine was having was it was not making enough energy to recharge my battery so after my battery died twice I figured my battery was bad, took it to autozone and they told me it was the alternator. So I got a re-man there and put it in.

[logantv]

i was JUST posting in another thread about how the coolant systems in bmw's STILL suck and have to be replaced around 60-70k. i wonder when (if) bmw will ever fix this weakpoint...

As an E30 guy I can tell you that they had it fixed at one point... My (pretty new to me) 2002 325i has almost 80k so I guess I should do a preventative swap soon.

[OUR2004BMW325i]

I'm hoping someone can help! We own a 2004 325i. The car has been overheating & we've replaced the expansion tank, bleeder screws twice (due to them melting when trying to bleed the lines) a new water pump, thermostat housing, upper house, coolant sensor located on or near the head was replaced, the list goes on. The test to see if the head or heads were cracked are showing negative at this point. We hope someone has some insight to bleeding the lines properly! (Just in case we are doing it incorrectly!) also, if someone knowledgeable might have an idea of what could be causing the car to continually overheat.
Seems we keep getting recommendations even by professionals that are more like a wild goose chase rather than informative information!
Thank you!!

[stevewav]

I know this is an old thread but I wanted to add my experience as it might help someone else as well.
My tank exploded as well while driving away from the school where I leave my kids in the morning.
There was snow everywhere and the temps bellow 0, and I was stuck in the traffic as the roads were not in the ideal condition...
All of the sudden I heard that awful noise and a lot of vapor started coming out of the engine bay.
The engine stalled but as I was just about to enter the roundabout with lots of cars behind me I had to restart it an move away.
Anyway I did some 100m without any water in the engine knowing I could do some irreparable damage to the engine but I could feel the frustration of the rest of the drivers behind me if I had decided to stay there....
The expansion tank had opened as a banana one one of its sides and the level indicator had disappeared.
I was pretty lucky to find a replacement part at the dealer as they usually need to order the parts here in Luxembourg.
It was a real PITA to get the old one out of there as the bent part had overcome the bottom security latch and was bushing against the inside of the part...
Anyway I managed to get the piece out and replace it.
I started refilling with coolant and surprise surprise the side tube was leaking. It was then that I realized that there must be an internal O ring that is now missing...
I have a set of various sizes of those at home so I found a similar size match but not the exact one (20x3 original, 20x2 mine).
At first I thought I was OK as the tube gave me some resistance going in but I was once more wrong.
The resistance was due to the fact , as I found out later, that the O ring does not stay in place when the tube is bushed in but it gets out of its place and of course it is ruined.
Silicon grease gave the solution to that problem. I resumed the refilling process and no leaks this time.
With the system full of fresh coolant I started the engine and waited to get worm in order to release the air from the valve, but for my surprise once more, I had tons of vapor coming out instead of air or coolant stream.
It was then that I realized there must be something else that doesn't work properly.
The day after I decided to restart the possess but with the help of my handheld scanner this time so that I can monitor both temperatures (engine and radiator outlet).
This time I was able to see the temp rising over 100 degrees but the electric fan did not engage !!!!
resetting the plug solved the issue but it was then that I realized that probably because the fan had stopped functioning the engine while at school had created a lot of vapor inside the engine that created so much pressure and caused the explosion of the expansion tank!!!
Unfortunately there was no warning, no overheating nothing that could have prevented this, so my advise is to regularly check that the fan is engaging from time to time, as the contacts with the age might become loose....