[Herakles]

Hey guys I have a 2011 335 , the coolant level has dropped down to warning light level a few times between long periods... I took the car to bmw dealer and they did a pressure test and didn't find any leaks-
I'm about to top it off again, but wondered if anyone knows about any issues like this?
It has 42k miles and the water pump
Was changed when it failed at 20k miles under warranty

[jwalker87]

I literally just solved this problem on my '08 335i last week. The bleeder screw on the expansion tank was weeping coolant ... sometimes. Just enough that it would randomly lose all the coolant in the tank and have the low level alarm on.

Fair warning, I initially tried to tighten it and the screw just snapped in half. Of course the engine was hot so a geyser of coolant then sprayed onto the underside of my hood until I smothered the whole thing with paper towels, lol. So make sure the engine is cold and/or just replace the expansion tank outright!

The tank on my '11 335i started leaking last year and I had to replace it, so it's probably time for you anyway.

[Herakles]

Originally Posted by jwalker87

I literally just solved this problem on my '08 335i last week. The bleeder screw on the expansion tank was weeping coolant ... sometimes. Just enough that it would randomly lose all the coolant in the tank and have the low level alarm on.

Fair warning, I initially tried to tighten it and the screw just snapped in half. Of course the engine was hot so a geyser of coolant then sprayed onto the underside of my hood until I smothered the whole thing with paper towels, lol. So make sure the engine is cold and/or just replace the expansion tank outright!

The tank on my '11 335i started leaking last year and I had to replace it, so it's probably time for you anyway.

Originally Posted by jwalker87

I literally just solved this problem on my '08 335i last week. The bleeder screw on the expansion tank was weeping coolant ... sometimes. Just enough that it would randomly lose all the coolant in the tank and have the low level alarm on.

Fair warning, I initially tried to tighten it and the screw just snapped in half. Of course the engine was hot so a geyser of coolant then sprayed onto the underside of my hood until I smothered the whole thing with paper towels, lol. So make sure the engine is cold and/or just replace the expansion tank outright!

The tank on my '11 335i started leaking last year and I had to replace it, so it's probably time for you anyway.

Thank you! I'll try to pay close attention to the tank ... is the bleeder screw on the tank? I don't think I noticed it ever

[Pladi]

Originally Posted by jwalker87

I literally just solved this problem on my '08 335i last week. The bleeder screw on the expansion tank was weeping coolant ... sometimes. Just enough that it would randomly lose all the coolant in the tank and have the low level alarm on.

Fair warning, I initially tried to tighten it and the screw just snapped in half. Of course the engine was hot so a geyser of coolant then sprayed onto the underside of my hood until I smothered the whole thing with paper towels, lol. So make sure the engine is cold and/or just replace the expansion tank outright!

The tank on my '11 335i started leaking last year and I had to replace it, so it's probably time for you anyway.

This has happened to me i second all of this.

Another very common spot is the oil filter housing gasket.

[jwalker87]

Originally Posted by Herakles

Thank you! I'll try to pay close attention to the tank ... is the bleeder screw on the tank? I don't think I noticed it ever

Yup; something like this image.

[Herakles]

I give up fellas- checked after tipping off a few weeks ago, level is below the high level mark- I use light to check for wet areas on the bottom pan and dry as a bone-
The expansion tank is dry as well.

I'm not sure if I should bother taking back to dealer or use a Indy shop in my area that works on bmw Porsche etc that's pretty reputable -

Guess I should explain maybe take the bottom cover off take for drove then throw on lift to see if anything

I think bmw dealer just did a pressure test

[Efthreeoh]

Originally Posted by Herakles

I give up fellas- checked after tipping off a few weeks ago, level is below the high level mark- I use light to check for wet areas on the bottom pan and dry as a bone-
The expansion tank is dry as well.

I'm not sure if I should bother taking back to dealer or use a Indy shop in my area that works on bmw Porsche etc that's pretty reputable -

Guess I should explain maybe take the bottom cover off take for drove then throw on lift to see if anything

I think bmw dealer just did a pressure test

How low was it? How warm was the coolant each time. If it was just slightly less, then it's just a fluid temperature thing. Cars use coolant over time, especially as they age; the reservoir cap is a pressure valve, so when the coolant gets hot, it vaporizes and the vapor escapes. The reservoir cap can weaken over time and let coolant as vapor press escape. If the dealer pressure tested the cooling system and it didn't leak, then it's not leaking. There is no dealership in the world that would find a leaking cooling system and NOT recommend you fix it. Hell, your lucky they were honest and didn't BS you into replacing something in the cooling system (like a cylinder head gasket or OFHG). They probably didn't check the pressure valve in the cap. The reservoir cap is under $20. If you are that concerned, then get a new cap and keep an eye on it. If the system has a small leak, you'd smell coolant, and a small leak always turns into a big leak in short order.

IMO BMWs owners, for some reason, are way to OCD - the internet just makes it worse. Relax, what your car is doing is most like normal coolant loss.

[tcphoto]

Strange, I would think that you'd find evidence on the belly pan. My history with my old E46 and now two years with the E92 tells me that it's probably an O Ring or plastic radiator piece that is degrading. I'd suggest going for a drive, getting it up to temperature and then pull the fan and look around the radiator and below. I remember going crazy looking for the leak on my E46 and it ended up being the ET mounting bracket.

[Herakles]

Tha is guys- forget to mention the dealer did install a new expansion tank cap - I do notice at the base of the expansion tank where the cap screws on some dried up looking coolant

My device advisor said coolant doesn't burn off like oil so I shouldn't be losing any.

[Efthreeoh]

Originally Posted by Herakles

Tha is guys- forget to mention the dealer did install a new expansion tank cap - I do notice at the base of the expansion tank where the cap screws on some dried up looking coolant

My device advisor said coolant doesn't burn off like oil so I shouldn't be losing any.

The service advisor is incorrect. Even a healthy engine with a healthy cooling system will slowly lose coolant over time.

[Herakles]

Originally Posted by Efthreeoh

The service advisor is incorrect. Even a healthy engine with a healthy cooling system will slowly lose coolant over time.

Well that makes me feel
Better !!

[Efthreeoh]

Originally Posted by Herakles

Well that makes me feel
Better !!

You never answered my question. How much did the level drop and what was the time interval it dropped over? You can't diagnose a cooling system problem without collecting some data. You could have overfilled the system last time; the level stick maxes out and the system is too full without indicating so by the level of the stick. The next time you checked the level could have dropped to normal.

[Herakles]

I fill it just above the max level - I haven't checked in a few weeks now and no light yet, but I'm sure it's getting low.

The question is if it gets close to empty low, there must def be a leak - period.

Bmw replaced the water pump about 3 years ago at 20k miles. I have 42k now. They didn't replace the thermostat when they did the pump I wish I had remembered to ask them to.

But again weird thing is not seeing the leak anywhere unless it's leaking into the oil somewhere if there is a gasket failure which then I'm really screwed

[Efthreeoh]

Originally Posted by Herakles

I fill it just above the max level - I haven't checked in a few weeks now and no light yet, but I'm sure it's getting low.

The question is if it gets close to empty low, there must def be a leak - period.

Bmw replaced the water pump about 3 years ago at 20k miles. I have 42k now. They didn't replace the thermostat when they did the pump I wish I had remembered to ask them to.

But again weird thing is not seeing the leak anywhere unless it's leaking into the oil somewhere if there is a gasket failure which then I'm really screwed

If it is leaking into the oil, it's only two places it can do that: at the cylinderhead gasket, and/or the OFHG. A properly executed pressure test would show those gaskets leaking. If the oil were to be contaminated it will show a milky-white gelled substance under the oil fill cap.

You said you filled it to just above max level. So, that is bad practice. Over filling the cooling system adds stress to it because the pressure inside the cooling system increases as the volume of the liquid expands when it gets hot and has less space to expand in. So over filling the cooling system can show a false consumption level as the system tries to equalize; it runs somewhere around 16 PSI, the cap will bleed off the excess coolant as that is the reason it has a pressure relief valve built into it. With the E90 system, you really can't tell the level of overfill since the measuring stick maxes out with very little increase of added coolant. For some reason BMW calls the coolant reservoir an "expansion tank", but it is not on the E9X. The reservoir is pressurized and holds coolant for the system. There is very little coolant reservoir space built into the radiator (i.e. no side tanks), so most of the coolant resides in the engine block, hoses, and coolant reservoir. True "expansion tanks" are not pressurized and are used in systems where the pressure relief valve is on the radiator built into the radiator cap and overfilling the system just bleeds the coolant into the un-pressurized expansion tank.

Get the coolant level correct and record the mileage and date, then every week, open the reservoir when the engine is cold and check the level. Do not refill the system until the low coolant light comes on. When it does, record the mileage, date, and amount of coolant added in ounces. Then you'll have some real data to help a mechanic diagnose if there is indeed a leak.

[ptpending]

i would like to add to that that you should not refill or add pure coolant, only mix with water at 50:50 ratio, because i''ve multiple times with problem with my plastic hoses broken at cold times -10 C due that i filled solid coolant to car
also the expanstion tank cap should be replaced every 3-4 year on petrol car due the reason it contains pressure valve with can not work after 3-4 years

[Herakles]

Thanks for your time replying- I just checked and the expansion tank looks almost empty - would have to be a good 3 weeks since I added coolant. I'm starting to get worried now that I'm leaking into the block, because there is no sign of coolant anywhere... this is so frustrating

To the last reply , I always dilute 50/50 wjen adding to expansion tank nomworrie there just where it's going

[Efthreeoh]

Originally Posted by Herakles

Thanks for your time replying- I just checked and the expansion tank looks almost empty - would have to be a good 3 weeks since I added coolant. I'm starting to get worried now that I'm leaking into the block, because there is no sign of coolant anywhere... this is so frustrating

To the last reply , I always dilute 50/50 wjen adding to expansion tank nomworrie there just where it's going

Well that is an unusual consumption rate. I can't believe if that is the true consumption rate the dealer's leak test did not find a problem with the cooling system. Perhaps it is the coolant reservoir itself.

[bluewater328]

Assuming based on comments you're checking the reservoir area, but have you also checked near the driver's side of the radiator as well? Seems to be a typical leak area (sometimes very slow). You might notice some white dried out drips around the area and the remainder would go along the radiator itself and get partially burned up as it trickled down.

That was a failure point of mine when it finally went. Sometimes you can even see the connection/tap the reservoir has to the upper hose leaking out the clamp.

Not sure you can lose that much that fast, but if there's a leak that wasn't detected by a pressure test, maybe a small deteriorating leak? I think the interesting/indicating part is that it's three weeks and the coolant reservoir is empty, but you haven't gotten a temperature warning yet.

[E92TiAg335i]

I'm subscribing!

2013 e92 n55 with 47k miles.

I don't have any leaks.

I noticed every 2-3 months, the coolant level is going from "max" to "min" in the expansion tank.

I always (ever so slightly) top it off.

Is this bad?

Should I be concerned about the car?

I don't know if this matters... but I live in South Florida.

[bluewater328]

Originally Posted by E92TiAg335i

I'm subscribing!

2013 e92 n55 with 47k miles.

I don't have any leaks.

I noticed every 2-3 months, the coolant level is going from "max" to "min" in the expansion tank.

I always (ever so slightly) top it off.

Is this bad?

Should I be concerned about the car?

I don't know if this matters... but I live in South Florida.

I wouldn't be if it were just that at that time interval. Top off and you're fine.

[Herakles]

Originally Posted by E92TiAg335i

I'm subscribing!

2013 e92 n55 with 47k miles.

I don't have any leaks.

I noticed every 2-3 months, the coolant level is going from "max" to "min" in the expansion tank.

I always (ever so slightly) top it off.

Is this bad?

Should I be concerned about the car?

I don't know if this matters... but I live in South Florida.

Originally Posted by E92TiAg335i

I'm subscribing!

2013 e92 n55 with 47k miles.

I don't have any leaks.

I noticed every 2-3 months, the coolant level is going from "max" to "min" in the expansion tank.

I always (ever so slightly) top it off.

Is this bad?

Should I be concerned about the car?

I don't know if this matters... but I live in South Florida.

My biggest worry is there a small internal leak- i might get a sample out of the expansion tank to see if it looks blue or any signs of chocolate milk look- but if it's mixing I think I'd see engine issues as well which I do not- it runs perfect

[abf.rio]

Originally Posted by Herakles

Hey guys I have a 2011 335 , the coolant level has dropped down to warning light level a few times between long periods... I took the car to bmw dealer and they did a pressure test and didn't find any leaks-
I'm about to top it off again, but wondered if anyone knows about any issues like this?
It has 42k miles and the water pump
Was changed when it failed at 20k miles under warranty

im having the same problem. no leaks, coolant reservoir is full and just had the tank replaced, but i keep getting the coolant light. Suggestions??

edit: it was just a sensor that was slightly bent in the coolant tank apparently.