Heater up to 80 deg + idling = Expansion Tank Failure??

So I just got done throwing down $2200 on new front brakes, rotors, front axles, tires and alignment.

When I picked up the car THIS MORNING from my mechanic, the heater seemed to be all the way up to 80, when I normally leave it at 68 or so. Well, I drove to work, and then back, and was idling in a parking lot waiting for a friend, and notice smoke coming out of the engine bay. I immediately shut off the car, get out, and notice there is fluid splattering all over the ground and spewing out from the bottom of the expansion tank (I think). Could the shop have done anything to provoke the failure?

I'm at 105k miles and I'm not sure if it's ever been replaced. It's very possible that it has before since I remember a few years ago the coolant light came on intermittently when it belonged to my dad.

Likely your friendly mechanic topped off the cooling system??

Unless your mechanic knows BMW's if they filled the expansion tank up to the top, you have your answer.

your ET (if original) will have a date sticker on it.. you can tell more or less now old it is.

Sent from my SGH-I727R using Bimmer App

Originally Posted by jfoj

Likely your friendly mechanic topped off the cooling system??

Unless your mechanic knows BMW's if they filled the expansion tank up to the top, you have your answer.

Ugh this makes me sick - they are a BMW & Benz shop, probably recommended on this forum somewhere because that's how I found them.

Ok, so the mechanic did admit to me that he topped off the tank. I have searched and found nothing about expansion tanks leaking only because they are topped off. If they're not supposed to be topped off, what do you do with it?

Might have just spewed out the cap....siphon, drive, inspect...

It's a definite crack, and I guess I will see it tomorrow. This also echoes what I saw yesterday as all of the coolant dripping out from somewhere on the side of the tank, and the cap was completely dry.

The tank is an "expansion" tank. It allows the coolant to expand as the engine warms up. The cap is rated at 2 bar (30 psi), too high in my opinion.

If you fill up expansion tank to the top, then the coolant cannot expand against an air pocket. If you were awake in Physics class liquids do not compress, but gasses do. Once air pocket is reduced/eliminated pressure rises very quickly, then weakest part fails.

There is a reference float in the tank that needs to be CAREFULLY used to verify coolant level. Once float is topped out, you can keep filling tank.

I always adjust float level based upon coolant temp, low float cold, nigh float warm. It you set high float level cold, you have less expansion space.

Originally Posted by OUTATIME

Ok, so the mechanic did admit to me that he topped off the tank. I have searched and found nothing about expansion tanks leaking only because they are topped off. If they're not supposed to be topped off, what do you do with it?

I bet your mechanic's top off caused this. A shop I went to did the same thing, and I noticed a leak that night after taking it home. I had no leaks before. I found that they had filled the radiator to the top. Take it back to him and tell him you understand the honest mistake, but you want that leak fixed. Explain to him the increased pressures that break seals as a result of over filling. The cooling system requires an air "cushion" to build pressure and allow for the expansion of fluid as it heats.

If you heat room temperature water to near boiling, it will expand by almost 5%. To hold it at it's original volume requires quite a bit of pressure. Water will have no problem bursting seals and blowing up a composite ET to make room for itself. Water IS compressible, but it just takes a great deal of pressure to make any sort of difference.



Looking at my steam tables, in order to keep water in the same volume from 70F to 200F, you have to apply over 12,000 psi. Have fun containing that. That sounds high though I'm gonna double check on some online tables.

EDIT: Wolfram Alpha confirms. wow that's insane.

Check YouTube for Mythbusters exploding water heater, this is what happened to you ET!

@12k PSI can't you turn water into diamonds?!

Originally Posted by jfoj

Check YouTube for Mythbusters exploding water heater, this is what happened to you ET!

@12k PSI can't you turn water into diamonds?!

You got me curious

Using a BARS device, diamonds are created at 1.7 million psi and 4500 F.

Assuming you compress the vapor pressure and close up the molecular bond/spacing with these crazy pressures.

30 PSI & a 10 year old expansion tank = red temp gauge.

Be curious to check the 10 year old expansion tank cap that has never likely opened to see if the cap is even any good?

I hear that there is a 1 Bar replacement for the newer BMW's that most parts departments hand out, be curious what the part number is?

Here is the cure for the E46/E39 6 cylinder cooling systems!

http://www.evanscooling.com/

Ok. I can confirm that the date on the part was 2001, which was the year the car was built. The mechanic also told me he doesn't literally "top" it off, but rather goes by the levels indicated on diagram. For now, I'm concluding he didn't really do anything wrong, and for that poor severed expansion tank, it was its time to go.

Originally Posted by OUTATIME

Ok. I can confirm that the date on the part was 2001, which was the year the car was built. The mechanic also told me he doesn't literally "top" it off, but rather goes by the levels indicated on diagram. For now, I'm concluding he didn't really do anything wrong, and for that poor severed expansion tank, it was its time to go.

That's good. It was probably just the oldness of the tank then.