Correct Coolant Level

[AtlasM3]

When I first go check the coolant level in the morning after the car has sat overnight it is right below the COLD text. Once I remove the cap it rises to the top of the KALT text after about 30 seconds. It’s done this for the past 2 weeks without losing any fluid. Is this normal? I’m guessing it might be a little too full since it’s going above the cold line.

[TheJordanWhitte]

Kalt is cold in German, if you aren’t losing fluid I’m not sure what your question is?

[AtlasM3]

Kalt is cold in German, if you aren’t losing fluid I’m not sure what your question is?

Sorry I know that was confusing. Should it be at the cold line after I open the cap or before?

[Nova1]

Opening the tank cap will not affect the coolant level when cold. When engine/fluides are cold the level should be at or very near to the Kalt/Cold level. Once the engine/fluid is brought to temperature it will go above that line. Once cool again it should settle back to Kalt. There are countless articles about the thermodynamics of this system online but that’s the simple principle of it.

[AtlasM3]

Opening the tank cap will not affect the coolant level when cold. When engine/fluides are cold the level should be at or very near to the Kalt/Cold level. Once the engine/fluid is brought to temperature it will go above that line. Once cool again it should settle back to Kalt. There are countless articles about the thermodynamics of this system online but that’s the simple principle of it.

I have been checking it first thing in the morning before I go to work. When I remove the cap the level rises about an inch or 2. From the bottom of the COLD text to the top of the KALT text.

[Nova1]

Personally, I would bleed the system to make sure as much air is removed as possible and then calibrate the level to Kalt when cold. Then recheck. After that I’m gonna have to defer to others with more experience.

[AtlasM3]

Personally, I would bleed the system to make sure as much air is removed as possible and then calibrate the level to Kalt when cold. Then recheck. After that I’m gonna have to defer to others with more experience.

I know it has to do with the pressure differential and once the cap is removed it frees up the small amount left in the system. I think it’s ok I’m probably just being over cautious.

[importbanana]

I have been checking it first thing in the morning before I go to work. When I remove the cap the level rises about an inch or 2. From the bottom of the COLD text to the top of the KALT text.

That means that there's a tiny bit of air left in the system somewhere. Nothing to worry about if you ask me. Just check it like once every few weeks, because it could be that at some point the air gets flushed out and then the level drops and stays at the lower position, and then you can fill up to KALT and then it's solved.

[AtlasM3]

That means that there's a tiny bit of air left in the system somewhere. Nothing to worry about if you ask me. Just check it like once every few weeks, because it could be that at some point the air gets flushed out and then the level drops and stays at the lower position, and then you can fill up to KALT and then it's solved.

Thank you! I figured this was the case but I just wanted to make sure! I will keep checking once a week until the air gets worked out.

[M3C]

If it does not get worked out, how old is the reservoir? This can be due to a broken inside reservoir pipe, a replacement would be the solution.

[AtlasM3]

If it does not get worked out, how old is the reservoir? This can be due to a broken inside reservoir pipe, a replacement would be the solution.

It’s a 97 with 74,000 miles on it. What part would be broken? I have a new reservoir with the cooling overhaul kit I’m planning to install next month.

[M3C]

You can't see it from outside but there are some interior walls including the long inside pipe that breaks due to heat and this causes coolant level change when opening the cap. Do you notice level slight drop when after starting the engine?

[BrianSalo]

You can't see it from outside but there are some interior walls including the long inside pipe that breaks due to heat and this causes coolant level change when opening the cap. Do you notice level slight drop when after starting the engine?

X2

The hose from the top of the radiator is connected to the vent port in the cap, and a tube internal to the expansion bottle that opens at the bottom of the reservoir below the fluid level.

When the internal tube is broken or separated from the lid: as the system cools air from the expansion bottle fills the little radiator hose and the top of the radiator then settles slightly above atmospheric. Pulling the cap off pushes a little water from everywhere back into the bottle.

Replace the expansion reservoir and it should stop happening. It probably won't hurt anything as it is but the system isn't bleeding air from the top of the rad correctly... and a 20 year old expansion bottle is a ticking time bomb.

It also could be a faulty cap that is holding significantly higher pressure than it should when the system is cold. Removing the cap causes all the rubber hoses to shrink and push coolant into the bottle. New expansion bottle and cap will fix both potential problems.

[AtlasM3]

X2

The hose from the top of the radiator is connected to the vent port in the cap, and a tube internal to the expansion bottle that opens at the bottom of the reservoir below the fluid level.

When the internal tube is broken or separated from the lid: as the system cools air from the expansion bottle fills the little radiator hose and the top of the radiator then settles slightly above atmospheric. Pulling the cap off pushes a little water from everywhere back into the bottle.

Replace the expansion reservoir and it should stop happening. It probably won't hurt anything as it is but the system isn't bleeding air from the top of the rad correctly... and a 20 year old expansion bottle is a ticking time bomb.

It also could be a faulty cap that is holding significantly higher pressure than it should when the system is cold. Removing the cap causes all the rubber hoses to shrink and push coolant into the bottle. New expansion bottle and cap will fix both potential problems.

This is great to know! I will go ahead and swap the cap but I hope the tank holds on a few more weeks. I daily drive the car so I won’t have a full weekend to do the work until after the holidays.

- - - Updated - - -

You can't see it from outside but there are some interior walls including the long inside pipe that breaks due to heat and this causes coolant level change when opening the cap. Do you notice level slight drop when after starting the engine?

I will check the level this weekend right when I start the car. Thank you for letting me know about this!

[AtlasM3]

X2

The hose from the top of the radiator is connected to the vent port in the cap, and a tube internal to the expansion bottle that opens at the bottom of the reservoir below the fluid level.

When the internal tube is broken or separated from the lid: as the system cools air from the expansion bottle fills the little radiator hose and the top of the radiator then settles slightly above atmospheric. Pulling the cap off pushes a little water from everywhere back into the bottle.

Replace the expansion reservoir and it should stop happening. It probably won't hurt anything as it is but the system isn't bleeding air from the top of the rad correctly... and a 20 year old expansion bottle is a ticking time bomb.

It also could be a faulty cap that is holding significantly higher pressure than it should when the system is cold. Removing the cap causes all the rubber hoses to shrink and push coolant into the bottle. New expansion bottle and cap will fix both potential problems.

I replaced the cap this weekend and checked the coolant level again this morning. When I opened the cap the level was about 1.5 inches above the cold line and it never got higher like it did with the old cap. This new level is about 0.5 inches higher that it was before with the old cap removed. So I’m guessing the old cap was failing and causing some issues but I didn’t think the level would go higher.

Should I wait and check it a few more mornings before I remove some of the coolant to get it to the cold line? I don’t want too much coolant to cause a pressure issue.

[scoobiedoo2029]

ive noticed my coolant level doing the same thing. it hasn't seemed to give me any issues. but i certainly do not remember the car doing this years ago. i had the car sitting for a few years only started/moved a few times.
when i resurrected my car in the free time in 2020, before i flushed the coolant i had no in cabin heat at idle/low rpm, changing the coolant and a new water pump fixed the issue. but in this time i noticed your issue of coolant leval rising when the car is dead cold.

ive been meaning to have the coolant checked for exaust gas im kinda thinking this might be a headgasket related issue the coolant system is apparently acting correctly by releasing any high pressure but there is still pressure build up that i dont recall ever being there before. the other thing im thinking is the heater valve might be able to keep a bit of coolant and be acting sticky somehow. i cant imagine an "air leak" sucking air ant not squirting coolant or at least smelling like it.


do bleed your coolant again. and then again. and then do it again with the front of the car lifted





fyi: using bmw blue coolant/water somewhere around 50/50 mix.

[AtlasM3]

Update: I checked the level again this morning when it was at the original level at the top of the KALT line. It was at this level as soon as I opened the cap and it didn’t change. It looks like the problem was a failing cap causing too much pressure in the system. Once it was removed all of the rubber hoses could shrink back down.

I’m still going to keep checking it a few more weeks before I do the cooling system overhaul.

[BrianSalo]

I'm flabbergasted that there exists an e36 that doesn't leak coolant. ha.

[BrianSalo]

Funny thing

I was poking around with an early 2000s land rover the other day, and it uses the exact same expansion bottle cap as BMWs.

The expansion bottle had a different design, and you could look into the top of the bottle and see a 'straw' sticking down that was aligned with the tube from the top of the radiator inlet end tank.

The Land Rover is probably easier to fill, burp, and self burp air out of the system since the expansion bottle is behind the right strut tower and higher than everything else in the cooling system.

[importbanana]

There were Land Rovers with BMW M52 engines from factory

https://www.roadandtrack.com/car-cul...the-red-mamba/