Check coolant level warning

Catastrophic failure narrowly averted... by sheer luck

I had my car into the dealer for work about 3 weeks ago. They replaced the lower radiator hose and the valve cover gasket. I drove 200 miles home without incident.

1 week later my wife tells me the care is "smoking" and the check coolant level warning came on. It was white "smoke". Thank God the car did not overheat. Nothing is more than a mile or two away and it is currently pretty cold here in the Pacific Northwest.

I took the cap off the coolant tank and the dip stick shot up out of the reservoir. I was thinking overfilled tank and maybe a bad sensor.

I had already searched the forum, so I was thinking maybe there was air in the lines. I looked at the bleeder screw. It was shorn off, hanging by a thread.

Thank you 'Fest for the hot screwdriver trick for removing the headless plastic screw.

I added a bunch of coolant, replaced the bleeder screw, and bled the system using the auxiliary pump. The warning light went out. No more "white smoke."

If you have any work done on your cooling system, check your coolant level and think about bleeding the system yourself (at least once). Twice in the past 6 months, a shop has tried to sabotage my car!

Originally Posted by drrico

I took the cap off the coolant tank and the dip stick shot up out of the reservoir. I was thinking overfilled tank and maybe a bad sensor.

Originally Posted by drrico

the bleeder screw. It was shorn off, hanging by a thread.

Originally Posted by drrico

added ... coolant, replaced the bleeder screw, and bled the system using the auxiliary pump. The warning light went out. No more "white smoke."

I'm confused.
- The warning light indicated a low coolant level
- A smoking engine often indicates coolant leaks
- Yet, the bobber indicated a high coolant level (inexplicably)
- The bleeder screw intimated a leak in the system
- Refilling the coolant (and bleeding properly) resolved the indications

So, everything indicated a leak ... except the bobber!

Does your bobber STILL shoot straight up now that the system is filled?

NOTE: This pic below of my expansion tank shows the proper level of the bobber.

Does your bobber still shoot straight up now that the system is filled?
No. Refilling the system AND closing the system with a new bleeder screw fixed everything.

The cooling system is supposed to be closed. When the hollow shafted bleed screw broke, the system became open, allowing air in through the bleeder screw opening and coolant to find its own level. So whatever coolant remained in the system leveled out. There was enough left to enter the overflow tank and raise the dipstick. When I turned the car on, the indicator correctly warned of low coolant level.

Once I bled the system and closed the new bleeder valve screw, the dipstick didn't move. If I open the bleeder screw, air creeps in and the dipstick rises as the fluid finds its level.

If this description is confusing, put some water in a tube, but don't fill it. Bend the tube into a "U" shape, covering one end with your thumb and leaving the other open. When you move the ends of the tube up and down, the fluid levels will be uneven. Move your thumb, uncovering the opening, so both are open and the two fluid level will remain even regardless of the position of the tube. That is what was happening in the cooling system. The broken bleeder screw uncovered the second opening in the system, allowing the fluid to level off.

Originally Posted by drrico

Once I bled the system and closed the new bleeder valve screw, the dipstick didn't move. If I open the bleeder screw, air creeps in and the dipstick rises as the fluid finds its level.

Thanks for the explanation. This is heretofore unknown to me.

To the rest of the tribal team here, ... May I ask ... is this what you've experienced also?

The reason I ask is a couple with a 325i that I previously posted about swears they filled the coolant but they kept getting the "low coolant" warning. They showed me the bobber sticking up almost two inches.

I always thought that meant the system is full. But drrico makes a case here that it could actually mean the system is low on coolant.

I'm confused. Can others confirm or deny this observation?

Q: If the bobber is sticking up high, can that possibly indicate LOW coolant?

I suppose it's possible. If the system hasn't been bled properly, the total volume in the cooling system would include the trapped air or vapor, displacing the coolant into the reservoir.

I am seeing something very similar:

Periodically, my car tells me "CHECK COOLANT LEVEL".

I go open the expansion tank cap (once the engine is confirmed cooled down) and the bobber pops way up out of the tank (I would assume this meant "TOO FULL").

I add more coolant until it 'looks full'. I realize this is a terrible description but I don't have a good unit of measure here. I usually add a couple cups of Coolant/Water.

The "CHECK COOLANT LEVEL" message goes away. After a few weeks, the message comes back. Rinse and Repeat.

I am preparing to do a complete coolant system replacement:
http://www.bimmerboard.com/forums/posts/199986

However, I thought it was very interesting that someone posted this exact issue, which apparently was indicating that the bobber was indicating 'FULL' when the car was indicating LOW COOLANT.

Normally such a simple task and BMW makes it so difficult. And sometimes VERY expensive.

now mine does the same thing. the bobber pops all the way up (more than nessercary). but when i use the a/c the check coolent light comes on and that never happens until i did that. is there something i can do to fix this?! i would like to use my a/c without having to worry that my car could mess up at any moment. if you guys have an idea please let me know. also the i just had the reservoir replaced. pm me if you can. thanks

in extreme temperature situations where the coolant in the radiator/engine block are boiling, the pressure will push any remaining fluid in the path of least resistance... the expansion tank.
the pressure and violent activity from the boil WILL cause the bobber to shoot up like a rocket when you remove the cap.

to wrap things up, the indicator stick should not be used or trusted at any point when steam is visible or hot stuff is dribbling out on your toes.