Massive Coolant Expansion Tank Crack - Cause?
 

Waiting on AAA right now as the engine was overheating.

There's a massive 4-6" long crack down the corner of the expansion tank and all the coolant spewed out.

What causes this kind of crack? Is it just because it's old and brittle or is there a deeper issue?

After replacing the Stuck Open thermostat a year ago, my temp gauge has been consistent and perfect ever since. This is a big surprise to me so I'm just hoping it's crappy plastic giving out.

Attached is the best pic I can get right now.

The overflow is pressurized, so age and brittleness makes it crack and leak. When was it last replaced if ever? Mine cracked from heat and brittleness, usually the red bobber snaps off as a sign that the rest of the tank is going too.

There's lots of plastic used for the hot, pressurized cooling system. It's not a question of if they will fail, but when. I replaced my entire cooling system in my car when I saw two places where the plastic cracked... I suggest you do as well if you plan to keep and drive the car long term.

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Not sure if you have an engine-driven fan (LCI V-8's don't), but check it if you do. When they go bad, temps (and pressures) can rise without it showing on the temp gauge since there's quite a range where the needle will stand straight up.

Check it by driving the car in stop and go, get it good an warm, then shut the engine off and see if there's significant resistance to turning the fan. If there isn't, you're fan clutch has given up the ghost and will contribute to the deterioration of the all the plastic parts in the cooling system.

Thanks y'all! I'll check the fan clutch after I replace the coolant tank on Tuesday.

Is that also an impact mark on your tank next to the hose connectors?

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Pretty common failure mode. Mine did the same @ ~110000. Split straight down that side.

Yeah, that's a 3.0. My engine-driven fan was borked which pressed the pusher fan into overtime service, which killed that fan. Once both were dead, POP!


The temperature gauge on these is 'buffered' so it reads straight up over a pretty broad range of temperatures. The problem with buffered gauge is that once it creeps over the straight up zone, it very rapidly jumps to red, not much if any warning. BMW did it to keep people from complaining the gauge moved, which is perfectly ordinary.



I put a Borg Warner (the only one I could get locally) clutch on it and now the fan roars a lot, worst when cold. I put a new Behr clutch on our other X5 and it does not roar when cold.

Attached is the reservoir tank now that it's out. Quite an impressive crack if I do say so myself haha.

Sitting in my garage waiting for Amazon to bring me my new one.

I'll check the fan clutch once the car is drivable again. Thanks for the tip!

What's worse is that my display in the gauge cluster is unreadable. The car "dinged" and I dismissed it initially. Then within seconds it dinged again. I carry a really really high power tactical LED flashlight on me at all times. You could say it's because I believe in the 2nd Amendment and that's just how I roll, but the truth is that I carry it because I have a 2006 BMW LOL. I've discovered that shining my LED light at my gauge cluster will allow me to read whatever error message it pops up.

When it said Coolant Temp High, my first reaction was "the sensor must be broken." Then I saw the coolant gauge maxed out. Still thought something must be broken. I stopped the car in the parking lot I was 5 seconds away from, popped the hood, and sure enough it was smoking.

The last overheating car I had was an 88 Camaro, and when that thing overheated you'd KNOW beyond a shadow of a doubt. Apparently the E53 doesn't spray the coolant directly onto your exhaust manifold so I didn't see any smoke lol.

Hopefully the fan Clutch is ok. I already have a driver door window track to replace that I don't feel like doing.

I see your crack and raise you a kaboom.

And the winner is.....!