May 8, 2006
Least reassuring comment of the year: Coolant Expansion Tank in E46
So recently I brought my car in for the 60k mile service.
Sure it set me back a bundle. Sure it discovered other problems that will set me back a bundle.
But the worst part was what had to be the least reassuring comment of the year: “You should expect to be stranded in the desert in the next 30k miles. You won’t know when it will happen. It will happen suddenly.”
Ok, so the fine folks at German Motor Specialists didn’t quite say that. But basically they told me that the coolant expansion tank in my car is known to crack after many thousands of miles, and that when it does it will be sudden, without warning. And then I’ll have to be towed.
I appreciate that they didn’t sell me on a new coolant expansion tank, and I appreciate their honesty, but this type of honesty sure doesn’t make you feel better. 
Guess I need to up my AAA membership level for safety.
In their display case of random parts, they actually had a coolant expansion tank, with the part that usually cracks highlighted in yellow:
I bet if these guys had a blog, their customer load would shoot up dramatically.
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12 Comments to “Least reassuring comment of the year: Coolant Expansion Tank in E46”
May 9th, 2006 at 8:57 pm
Doesn’t someone make an aftermarket aluminum expansion tank? There are several available for third-generation RX-7s, for example.
You appreciate they didn’t sell you a new tank? You should get one. Loss of coolant can mean something a lot worse than getting towed.
May 9th, 2006 at 10:10 pm
It sure can. After several burst hoses incidents while traveling, I once blew a head gasket, which necessitated a new engine head. Or rather two. This was on a Jaguar XJS 12-cylinder, which had two heads. This was not an inexpensive repair.
You want to replace that tank. Dennis. Now, not when it blows.
May 9th, 2006 at 10:28 pm
Hm… second thoughts ahoy
November 25th, 2006 at 6:04 pm
mine just blew today… at 66K miles. I am sooooo lucky… didn’t have the cell phone with me. I poured in some water, watched it all drain out instantly, hopped in the car, and prayed I could make it home 15 miles away w/o overheating in very dangerous neighborhoods or on the shoulderless highway. Lucky me. I made it. Do yourself a favor.. replace it. Mine cracked exactly where they drew the crack.
November 28th, 2006 at 7:45 pm
yeah mine too. it did not crack but the lower half was leaking bad…
the piece tht connect the lower half.. to the expansion tank.. I was surprise just as you.. the tank did not break.. so better replace the lower piece to that expansion tank..
July 23rd, 2007 at 8:53 am
Mine went last Friday with explosive results. I was sitting in a McDonalds drive through eating my lunch and I didn’t notice the temp gauge creaping up to the red. A hose poped or the tank blew up, emptying the contents of my radiator onto the ground
I had to get the car towed to a garage. They told me today that the expansion tank was cracked. Change your if you have a chance at your next service. Cheaper in the long run
August 10th, 2007 at 6:43 am
haha — mine ruptured last night - exact same spot as in the picture. I noticed it just as I was pulling into the driveway - the temp gauge is either broken or it had just happened because it was still showing regular temperature. Smoke (steam) started coming out from under the hood. I popped the hood and squeezed the upper hose and it was empty! I opened the cap and the tank was bone dry….poured water in and it gushed out from the side! I’ll be replacing it today! $165 for the tank and cap!
I’ll change it myself!
November 6th, 2007 at 2:54 am
Mine cracked yesterday…exactly as per drawing. I had to try a quick fix to get to the garage Used some a sealant which took me a few kilometres and gave way too. I am now faced with a $190 bill for a new expansion tank. I hope that I will not need a cap too. Can someone tell me how to DIY??
December 13th, 2007 at 12:44 am
Lol…my blew in McDonalds parking lot too…that’s so funny.
December 22nd, 2007 at 7:33 pm
Mine poped exactly as highlighted in the picture last week. Ordered parts online costed meabout 150$ (tank + support bracket + ATF thermostat). You have to change all those three together because they are kind of stuck together.
The problem I have now is the engine still get overheat with new tank installed. Maybe got a bad thermostat.
January 20th, 2008 at 2:56 pm
I lost the expansion tank on my 330ci a year ago. But it had help. The cooling system was being pressurized beyond design parameters by a small compression leak from the #1 cylinder into the water jacket. Over time this weakens the tank further at its typical weak points. The result was explosive failure. It took awhile to convince the dealer that this was the trouble but they finally pulled the head, surfaced it and put in a new head gasket. Problem gone. To test if this is happening to yours, look for dried anti-freeze around the filler cap. Or, best of all, after the engine has cooled, preferably in the morning before starting it for the day, crack the filler cap and note if you hear any pressure escape. There should be none at all. Even any slight hiss will tell you that your system is being pressurized by something other that the water getting hot.
July 9th, 2008 at 12:55 pm
Mine just ruptured in the exact spot where they drew the circles on. I’ve done plenty of research and this seems to be a common problem due to the structure of the tank. Love BMW but I hate their cooling system design. If anyone decides to change a tank yourself is very easy but be particularly careful when pulling out the tank since there is this spring valve in the larger opening at the bottom of the tank and if you yank too hard this will break. Is a very bad design too. So just be careful and try to pull it as straight up as possible.
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