Coolant Tank EXPLOSION

494 Views 20 Replies 10 Participants Last post by tks, 15 h ago

AG-E46

Discussion Starter · 4 d ago

2

Hi there,

First of all I just wanted to thank everyone who participates on these forums - without you guys owning an E46 would be an extremely expensive endeavour.

So last night I was driving on the highway at 110 kmh (65mph) and I looked down at my gauge cluster to see the temperature needle fully in the red - I've owned my 2005 325XI since January and have never had this happen to me. The needle has always been steady in the middle, even while driving through Mountain passes in +30C weather.

Before I even had a chance to pull over I heard a loud pop underneath my hood followed by billowing clouds of evaporated coolant that spewed all over the engine. Short story - I get it towed home and got into it today.

I have noticed a whining noise around 1500-2000rpm that started happening last week - I assumed it was the power steering system since it has been slowly leaking P/S fluid since I bought the car and I have been meaning to replace it anyways. I am now wondering if it was my water pump making these noises.

My question is - has anyone experienced a literal explosion of their expansion tank before? If so - would a seized or broken water pump cause the engine to overheat to the point that the head gasket blew and sent cylinder compression into the cooling system, causing the rapid disassembly of my expansion tank? I saw that Mango responded to a similar post saying that the head gasket was likely fcked but I am hoping that is not the case here.

Thank you to anyone for some input, it's my first E46 and I thought the previous owner had completed the water pump upgrade - but maybe not. Hoping to get a replacement tank, new belts etc. In the next few days. Praying to the E46 God that my cylinder head is fine and the rapid disassembly was just caused by coolant expanding too much.

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cigma2312

· #2 · 4 d ago

Your first stop will be to check cylinder compression and leak down. If those numbers are good then you maybe lucky. All I can say is best of luck.

Reactions: 1

Sapote

· #3 · 4 d ago

cigma2312 said:
Your first stop will be to check cylinder compression and leak down

These test are not so helpful in this case. Even if the gasket is leaking, it's so small that the tests will not be able to detect it.

Reactions: 1

Sapote

· #4 · 4 d ago

AG-E46 said:
see the temperature needle fully in the red

Did the small red LED light came on?
In this case, the engine overheated first, created a lot of steam/gas and the expanded volume led to the tank rupturing.

I'm not sure what caused the overheat; could be low coolant. Don't depend on the coolant light unless you had tested that it worked with low coolant in the tank. When is the last time the coolant level in the tank was checked?

The main thing right now is to check if the head or gasket has been damage by the overheat. So replace the tank, fill water, bleed the air properly and drive with an eye on the temp gauge, and check the coolant level couple time per week to see if the level stable or lowering. But I would plan for the worst that the head might need to be out.

AG-E46

Discussion Starter · #5 · 4 d ago

Sapote said:
Did the small red LED light came on?
In this case, the engine overheated first, created a lot of steam/gas and the expanded volume led to the tank rupturing.

I'm not sure what caused the overheat; could be low coolant. Don't depend on the coolant light unless you had tested that it worked with low coolant in the tank. When is the last time the coolant level in the tank was checked?

The main thing right now is to check if the head or gasket has been damage by the overheat. So replace the tank, fill water, bleed the air properly and drive with an eye on the temp gauge, and check the coolant level couple time per week to see if the level stable or lowering. But I would plan for the worst that the head might need to be out.

I don't believe the red led came on - the needle was just deep in the red. I checked the coolant the previous day as I was driving a long distance and everything was looking good. The floater was lined up with the top of the expansion tank.

Appreciate your response a lot. I'll get the tank and other damaged components replaced and send an update once it's back running again.

AG-E46

Discussion Starter · #6 · 4 d ago

AG-E46 said:
I don't believe the red led came on - the needle was just deep in the red. I checked the coolant the previous day as I was driving a long distance and everything was looking good. The floater was lined up with the top of the expansion tank.

Appreciate your response a lot. I'll get the tank and other damaged components replaced and send an update once it's back running again.

Forgot to mention - after the expansion tank exploded the low coolant light did come on which makes sense because there was not a drop of coolant left in that engine. The amber oil light also came on after I turned the engine off which is interesting. Checked the oil - not milky yet and it was above 1/4" above the min. line.

Sapote

· #7 · 4 d ago

AG-E46 said:
Forgot to mention - after the expansion tank exploded the low coolant light did come on which makes sense because there was not a drop of coolant left in that engine. The amber oil light also came on after I turned the engine off which is interesting. Checked the oil - not milky yet and it was above 1/4" above the min. line.

This means the coolant level is working, but not all tanks have proper working sensors, so it must be verified before relying on its light.
The oil light means t=oil is a bit low, nothing to do with the event.
Things to check after repair: feel how hard the coolant upper hose after a drive. It should be firm like a 29psi but not super hard, which indicates combustion gas leaked into the coolant.
The next cold morning I would remove all spark plugs and look careful for condensation around the tip. If wet then coolant got in.

Sapote

· #8 · 4 d ago

So you didn't see the yellow coolant level light before the overheating?
With the tank intact, the only way to cause overheat is either low coolant, or no coolant flow, or electric fan not running.

AG-E46

Discussion Starter · #9 · 4 d ago

Sapote said:
So you didn't see the yellow coolant level light before the overheating?
With the tank intact, the only way to cause overheat is either low coolant, or no coolant flow, or electric fan not running.

I'll go through the steps you mentioned above once I get it back to running condition, but yeah I have never had the yellow coolant light come on whilst I've owned this car. I regularly check my fluids ever week and have never noticed a drop in coolant level.

Is there a possibility that the thermostat could have seized closed? I know their supposed to be a fail safe that they will stay open, but I'm starting to wonder if that might be the case. Anyways, I'll update you as the repair goes on.

Thank you Sapote!!

markusmarkus

· #10 · 4 d ago

Thermostats are designed to fail open. What’s the maintenance history for the cooling system?

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OnTheFence

· #11 · 4 d ago

Yes, the expansion tank can loudly pop.
Did you see if you can see the crack in the expansion tank?

Even with no coolant, you can start the car cold for a minute or two and see if it idles correctly.
This may tell you if there is overheat damage

OnTheFence

· #12 · 4 d ago

Sapote said:
With the tank intact, the only way to cause overheat is either low coolant, or no coolant flow, or electric fan not running.

He said the tank exploded

Effduration

· #13 · 4 d ago

I am reading an overheat at highway speeds followed by an expansion tank failure.

-Not a fan problem
-Not likely a leak or a low coolant problem - you checked levels
-Doesn't sound like an air pocket problem either- would have happened sooner

I am betting a flow problem.. most likely failed water pump or some kind of clog in the system.. I wonder if anybody ever used stop leak in your car's coolant system

These cars don't take overheats well, and by the time the gauge goes red, its too damn hot (the gauge is buffered from factory so that it stays in the middle over a wide range of temps..like 75c - 110c or something). As Sapote said you need to see if your head is warped or head gasket is compromised. Not the end of the world...These engines do take head gasket replacements well.

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LeverThis

· #14 · 4 d ago

The expansion tanks are known to split & crack along that seam, though usually not quite so spectacularly. I had a Behr Hella ET that lasted only 88k miles & barely 5 years; it cracked on that same corner but the split was only a couple inches long.

Use distilled water when you put it back together until you know if the HG is good or not, and that other components are good or are replaced once HG is confirmed good.

Radiators have plastic end caps that with age also tend to leak at the seams or split.
Coolant hoses with oil on them or ATF fluid from power steering leak dripping on them are also suspect.
Plus if original, the coolant hose orings might not reseal well upon reassembly.

One rough test for combustion gas leakage into coolant is feeling the upper rad hose on a cold start to see if it "inflates" like a balloon before the coolant has warmed up and thermally expanded, like within a minute or so of start up.

On cold engine, open expansion tank cap & close it. Upper rad hose should be pliable. Start engine and idle, if upper hose gets hard/inflated before coolant/water has warmed up that indicates a possible HG issue.

Water pump flow you can test, again on a cold engine, by removing ET cap and revving engine up to 2k or 2.5k rpm or so while looking down into ET to see if a stream of coolant is shooting from the side when it revs up. Use a helper or set up a camera to observe, and only run engine briefly with ET cap removed.

As noted above, temp gauge is near useless due to being buffered at 12 o'clock from 75c to 115c. You can use the hidden test menu on instrument cluster to display the actual coolant temps. Select test 7.0. See link in my signature below.

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LeverThis

· #15 · 4 d ago

Sapote said:
These test are not so helpful in this case. Even if the gasket is leaking, it's so small that the tests will not be able to detect it.

A compression test definitely might not reveal an HG issue, though it wouldn’t hurt to do one. However, a leakdown test should be able to in many if not most cases. Less false negatives than from a compression test.

A friend's 325i had good compression and actually ran great; aside from intermittent cold start misfires, unexplained coolant loss and lack of heat in cabin. Leakdown test revealed air bubbles in ET from 2 or 3 cylinders.

Reactions: 1

TobyB

· #16 · 4 d ago

there was not a drop of coolant left in that engine.

bummer.

t
would pressurize things and see if they leaked into other things.

Kolonel-Black-Fox

· #17 · 3 d ago

Dear Pal,

If it means anything apparently the red means too late. I’m constantly peaking at my dash, I know I’m not paranoid. I have read of other folks hitting the overheating mark and being there for minutes and still not having a destroyed engine. So hopefully the Lords have blessed you.

In my experience though I Haven’t ever ran out of coolant in the entire engine. Even when I had cracked or exploded hoses and tanks. The system itself still had coolant. I believe to completely empty the coolant there is another area other than the radiator.

Hope that’s reassuring. I do remember after a coolant refresh I had what seemed like a bad bleed job and the temp gauge spiked while I drove the bloc home wasn’t far but the light really scared me and I shut off asap. Just a bad air pocket is what I summarized, I have a steady idle now and no engine issues that I can tell and it drives fine so maybe these engines aren’t as brittle as the warning is. Still no more overheating.

Cheers.

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Sapote

· #18 · 3 d ago

markusmarkus said:
Thermostats are designed to fail open.

By what mechanism? To me, if the wax motor leaking wax, then it won't open.

Sapote

· #19 · 3 d ago

OnTheFence said:
He said the tank exploded

Exploded as the result of after being overheated with an intact tank.

Sapote

· #20 · 3 d ago

AG-E46 said:
Is there a possibility that the thermostat could have seized closed? I know their supposed to be a fail safe that they will stay open, but I'm starting to wonder if that might be the case.

Was the engine cold at the beginning of the trip? If yes, then how many miles driving before the overheat happened? Did you see the temp reach 12 o'clock for sometime before overheating? The information can help to determine if the Tstat failed close or something else.

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