Expansion tank exploded

[jthrongard]

Car details - 2000 2.3 manual with 89,000 miles. I bought the car about 6 months ago and just got it to point where I felt good about highway driving. Need radiator, new hoses, new water pump, new belts, new fan and fan clutch. Outside of that I don't know what work has been done. No white smoke. Oil is good brown (but only has handful of minutes on it) and no oil in coolant that I could see (before it blew up).

The scenario: Drove it down highway for about 20 miles. I wasn't gentle but never revved above 5.5k RPMs. Car parked for about 4 hours (to re-stitch the rear window zipper and install a new one). Drove back a little more aggressively but not outrageous - maybe up to 6k in a few shifts for about 8 miles. Slowed down from 55MPH to about 25MPH entering a little town. After about 1/2 mile at that speed I hear a LOUD bang under hood. I thought I threw a rod it was that loud. Notice fluid all over in rear view. Start to pull over and see temp light come on. Kill motor and coast a few more yards. Maybe had engine running for 30 feet from the pop so 5-10 seconds. As you can see in images the expansion tank exploded. It ruptured the side, underneath and blew the top off its seam.

I guarantee this is the original tank as based on other items that hadn't been changed that are typical. When I bled the coolant system, I MAY have not done it right. I know I ran the heater and unscrewed the bleeder but I remember thinking it was weird because no coolant came out like I had done on another Z3 I owned. Lastly, I've seen coolant puddled around the base of the cap.

My worry of course is HG. But there's such low miles for that and no other symptoms that I'm aware of. Could it just be old and ready to pop? Could there have been air in the system? How could there be such pressure to make it rupture like a bomb and not just split and drain out?

 

[Zephyr]

They do this. Especially at M52 engines.
Probably heard this more than ten times when I was member of the bmw club.

 

[SV8Predator]

They do this. Especially at M52 engines.
Probably heard this more than ten times when I was member of the bmw club.

That's great info. What's the reason and the cure?

 

[Duncodin]

Thermostat housing too. Mine popped a while ago. Probably due to pop again soon. I think I'll change it along with other plastic cooling system bits. It'll keep me busy. As in "Sorry luv, can't clean the grout in the bathroom. Too busy doing important maintenance man stuff in the garage".

 

[Rudyrov]

As to the state of the head gasket, there are variety of easy test that you can perform to get a general feeling of what’s going on. Nothing of course like actually taking a look inside the engine, but you can do compression test a leak down test and look for contaminated oil.
Why did the tank burst, most likely fatigue and heat cycles etc.

 

[Zephyr]

That's great info. What's the reason and the cure?

The reason is bad quality. The cure is either a Turner aluminium one, or a newer updated one.

 

[Duncodin]

Anyone have recomendations for replacement parts? ie not cheap no-name stuff.

 

[Zephyr]

OEM new ones as safe, and of course Turner (made to order at about $ 600).

 

[the Nefyn cat]

Mmmm. Plastic item, cycled from cold to hot and back again many many times, and 24 years old, too. Why would it go bang? Just one of those things that happens, unfortunately. Bit like the dried-up "used-to-be-rubber" gaskets and many other bits.

 

[Stevo7682]

As others have said age is a big player here plastic gets very brittle.
Secondary issue with 6cyl is excess pressure in system caused by incorrect system bleeding after coolant repair work leading to an airlock that expands in hot engine causing excess pressure

Stephen.

 

[Kiwipom]

Car details - 2000 2.3 manual with 89,000 miles. I bought the car about 6 months ago and just got it to point where I felt good about highway driving. Need radiator, new hoses, new water pump, new belts, new fan and fan clutch. Outside of that I don't know what work has been done. No white smoke. Oil is good brown (but only has handful of minutes on it) and no oil in coolant that I could see (before it blew up).

The scenario: Drove it down highway for about 20 miles. I wasn't gentle but never revved above 5.5k RPMs. Car parked for about 4 hours (to re-stitch the rear window zipper and install a new one). Drove back a little more aggressively but not outrageous - maybe up to 6k in a few shifts for about 8 miles. Slowed down from 55MPH to about 25MPH entering a little town. After about 1/2 mile at that speed I hear a LOUD bang under hood. I thought I threw a rod it was that loud. Notice fluid all over in rear view. Start to pull over and see temp light come on. Kill motor and coast a few more yards. Maybe had engine running for 30 feet from the pop so 5-10 seconds. As you can see in images the expansion tank exploded. It ruptured the side, underneath and blew the top off its seam.

I guarantee this is the original tank as based on other items that hadn't been changed that are typical. When I bled the coolant system, I MAY have not done it right. I know I ran the heater and unscrewed the bleeder but I remember thinking it was weird because no coolant came out like I had done on another Z3 I owned. Lastly, I've seen coolant puddled around the base of the cap.

My worry of course is HG. But there's such low miles for that and no other symptoms that I'm aware of. Could it just be old and ready to pop? Could there have been air in the system? How could there be such pressure to make it rupture like a bomb and not just split and drain out?

The pressure cap should prevent excessive pressure build up in the pressurised parts of the system, which includes the tank, regardless of any air locks. Might pay to get a new cap. The plastic tanks do fail, due to age, it happens on other cars eg my ‘96 land rover discovery. I would expect a slow leak first but a blow up like this can happen as well I guess.

 

[OhioZ4]

I believe Ill be on expansion tank #3 when I get to snooping around . I replaced the one that came with the car after it split . The replacement busted after a month or two , covered under warranty , it gets replaced . The last time I was in the car , in the Fall , the light came on as I was pulling out of the garage , after a quick check , it looks like it has given up the ghost too . Im guessing its cheap Chinese garbage is the reason why .