2015 sDrive 35i frustrating coolant disappearing act

[james92se]

2015 X5 sDrive 35i - 187k miles

Received a sudden low coolant warning in late March out of the blue. Checked coolant and it was low and upon monitoring it that day kept finding coolant down below/around the coolant tank. Parking it would leave big puddles directly from/under the coolant tank.

I put dye in the system so I could monitor it over the next few weeks and while waiting on parts to arrive. Never a single trace of dye/coolant anywhere except in/around the coolant tank. I read that apparently the coolant tank is a common issue in which it cracks.

I replaced (all from FCP Euro) these three items just to rule everything out in that area:

Coolant tank
Tank cap
Heater valve

There is no longer any discernable leak - no puddles, no streams of visible dye with the UV light etc. yet it's still eating coolant. I have gone through at least 6-7 gallons the past month but it always disappears. Sometimes I get a few hundred miles, sometimes I only 15-20 miles and without fail it's all gone again. It definitely consumes it much, much faster in hotter weather.

Each time, there's a bit of coolant on top of the tank as if it's spit it up from boiling over or being overpressurized or something, but beyond that I can't find ANY trace of where the coolant is going. The coolant temperature is always fine/normal as well so it doesn't appear to be running hot or actually overheating or boiling over or anything. Again, no puddles, visible leaks, or anything except a few drops of coolant on TOP of the coolant tank each time.

There's no way it's going into the oil as I've drained a pinch (Fumoto drain valve installed) and can't find any trace of the UV dye or traditional milkshake consistency from bad head gasket. Plus, there's no way the engine has consumed multiple gallons of coolant in such a short time without hydro locking or something.

The water pump and thermostat are just over a year and 20k miles old and I've self bleeding procedure done each time I've opened up the coolant system.

Where is this coolant going? Is there some hidden coolant pipe in a valley or something on the engine I should further investigate that I'm not seeing? Any other tips or hints? Anybody deal with anything similar that was more than just the coolant tank itself?

[james92se]

Welp, nobody replied here but I'll still follow this up.

I pressure tested the entire system and couldn't find any leaks. Eventually determined it appears to consistently be over-pressurizing/boiling over and puking it all out of the coolant tank cap.

Ran a chemical block test on it (multiple times), and unfortunately consistently indicating exhaust gasses in the coolant. Likely bad head gasket, but I guess theoretically could be a cracked head or block.

So - I don't suppose anybody has ever done a head gasket on one of these? I can't find anybody online that has. I'm just curious if I'll need any goofy BMW specialty tools etc.

In addition to this, I'm also now getting a 20A701 coolant pump speed out of tolerance error (and displays "error status: error stored"). The water pump and thermostat are only a little over a year old and 26k miles on them. Does this error indicate a failed pump or is it just some expected/unimportant error as a result of all the bleeding attempts etc?

*edit* Forgot to add no need for any potential keyboard warriors to pounce on the green coolant. I assure you I'm using the correct "blue" coolant - I just have UV dye in the system to help me check for leaks and it turns it this bright green color.

[tfunk88]

Man, sorry I missed this post when you made it earlier but as soon as I was reading it I thought “headgasket”. That sucks.

I’m assuming you’ll need specialty tools as changing the headgasket means removing the head. Which means all the cams/timing stuff will have to be released and reinstalled correctly.

[james92se]

Originally Posted by tfunk88

Man, sorry I missed this post when you made it earlier but as soon as I was reading it I thought “headgasket”. That sucks.

I’m assuming you’ll need specialty tools as changing the headgasket means removing the head. Which means all the cams/timing stuff will have to be released and reinstalled correctly.

Yeah, knowing how cramped the bay is, especially the firewall area and remembering how annoying even the valve cover/gasket replacement was... I can only imagine how awful this will be doing it with the engine still in the car.

Wish I could find some good info online about the job/parts/specs without having to pay $30 for one day for BMWTIS.

[tfunk88]

Yep, I’m going to be doing valve cover gaskets on my 50i this summer…ask me how much I’m looking forward to that 😂

[yupetc]

I've taken the motor out for a forged rebuild before, head gasket is easiest and most confident if you do it with the motor out of the car. 6 months later, with some issues with the head's fuel injector port being washed out, I had to pull that head out of the car, this time I did the head job with the motor still attached in the bay. Not the hardest to do if you manage to remove the whole front end so you can just stand right in front of the motor and access timing chain this way.

Also, just my suspicion, if your head gasket is bad and if coolant is communicating with the exhaust gases, shouldn't you also be dealing with loss of compression along with drivability issues? That's something to check before you go yanking that head off. It's not a big job to do the head, but it does take some deeper dive effort to get it done.

[james92se]

Originally Posted by yupetc

Also, just my suspicion, if your head gasket is bad and if coolant is communicating with the exhaust gases, shouldn't you also be dealing with loss of compression along with drivability issues? That's something to check before you go yanking that head off. It's not a big job to do the head, but it does take some deeper dive effort to get it done.

Absolutely in most cases and that's why the head gasket is the last thing I was expecting. It has absolutely no symptoms except the puddles initially when I replaced the coolant tank/cap and ever since then every drive boils the coolant and spits out the top.

I have always heard of the "no symptom" head gasket failures but never experienced one myself. Mine have always been fairly obvious. I haven't super studied this engine but I figured maybe the direct injection or turbo or something was allowing the coolant to burn up somehow without going through the oiling system.

I'm definitely still trying to find reasons to justify to myself to NOT pull the head off, but I'm also only able to work on it on the weekends and everything I do that turns out to be fruitless just wastes more time on it ya know?

Again, I do also have that coolant pump speed out of tolerance error even though the pump only has 26k miles on it - in your experience does this error indicate an actual faulty pump?

Cool to see you've done a lot of work on these - are there any specialty tools I might need if I DO end up pulling the head?

[tfunk88]

I had a Ford 6.0 that the headgasket was leaking on 3 cylinders. Only symptom was some coolant puking occasionally when I got in it hard. No loss of power. But the coolant hoses would become pressurized right quick! Lol

[Tomcat_F15_STL]

Your electric water pump is probably malfunctioning and overheating your engine.

I do not get the impression N55 suffer many head gasket failures.

[yupetc]

Originally Posted by james92se

Absolutely in most cases and that's why the head gasket is the last thing I was expecting. It has absolutely no symptoms except the puddles initially when I replaced the coolant tank/cap and ever since then every drive boils the coolant and spits out the top.

I have always heard of the "no symptom" head gasket failures but never experienced one myself. Mine have always been fairly obvious. I haven't super studied this engine but I figured maybe the direct injection or turbo or something was allowing the coolant to burn up somehow without going through the oiling system.

I'm definitely still trying to find reasons to justify to myself to NOT pull the head off, but I'm also only able to work on it on the weekends and everything I do that turns out to be fruitless just wastes more time on it ya know?

Again, I do also have that coolant pump speed out of tolerance error even though the pump only has 26k miles on it - in your experience does this error indicate an actual faulty pump?

Cool to see you've done a lot of work on these - are there any specialty tools I might need if I DO end up pulling the head?

Like others are saying, I also won't suspect the head gasket seeing how next to zero the N55 has head gasket cases.

But if you're going to do the head, you'll at least need the timing tool kit. There's a bunch of these circulating on eBay and Amazon, it's your pick. But note that some of them aren't made very well. I've had to buy 3 kits and mix-match the pieces until I get a perfect kit. The flywheel key tends to bend when I had to torque up the crank pulley bolt. In your case, unless you'll also replace the timing chain, I'd suggest you to leave that crank bolt alone. Just get the guides replaced and you should be fine. I see your profile indicates you're in Texas, where abouts are ya, if I'm close enough, I can be within reach as a backup plan.

[james92se]

Originally Posted by Tomcat_F15_STL

Your electric water pump is probably malfunctioning and overheating your engine.

I do not get the impression N55 suffer many head gasket failures.

The more I think about this I believe I'm going to first do the water pump and thermostat again first. They're from FCP Euro so I should be able to warranty them.

I can't imagine how the chemical block test is wrong though, but I did have some trouble getting the rubber cone in there without sucking up coolant. The cone itself bottoms out on the yellow max/min fill line, which I kept having to wipe dry.

Then, as the car warmed up, and the coolant kept rising (and ultimately boiling over) it became a back and forth battle to get a reading before the coolant boiled back up to the rubber cone and potentially sucked into the tube.

I ordered another style of test kit, the kind that is a little packet you dangle down into the coolant and it changes colors in the presence of. I'll do that one too this weekend out of curiosity.

[yupetc]

Originally Posted by james92se

The more I think about this I believe I'm going to first do the water pump and thermostat again first. They're from FCP Euro so I should be able to warranty them.

I can't imagine how the chemical block test is wrong though, but I did have some trouble getting the rubber cone in there without sucking up coolant. The cone itself bottoms out on the yellow max/min fill line, which I kept having to wipe dry.

Then, as the car warmed up, and the coolant kept rising (and ultimately boiling over) it became a back and forth battle to get a reading before the coolant boiled back up to the rubber cone and potentially sucked into the tube.

I ordered another style of test kit, the kind that is a little packet you dangle down into the coolant and it changes colors in the presence of. I'll do that one too this weekend out of curiosity.

Whoa, this sounds to me like your T-stat can be a suspect. And if you get a pump speed error, you might as well change out the water pump. With FCPeuro backing you, it's just a matter of time being spent and a little bit of return shipping cost. No big deal.

[james92se]

Originally Posted by yupetc

Like others are saying, I also won't suspect the head gasket seeing how next to zero the N55 has head gasket cases.

But if you're going to do the head, you'll at least need the timing tool kit. There's a bunch of these circulating on eBay and Amazon, it's your pick. But note that some of them aren't made very well. I've had to buy 3 kits and mix-match the pieces until I get a perfect kit. The flywheel key tends to bend when I had to torque up the crank pulley bolt. In your case, unless you'll also replace the timing chain, I'd suggest you to leave that crank bolt alone. Just get the guides replaced and you should be fine. I see your profile indicates you're in Texas, where abouts are ya, if I'm close enough, I can be within reach as a backup plan.

Yeah, I definitely don't care to replace the timing chain unless I absolutely have to for some reason.

Regarding the timing tool kit, are we talking about something like this (attachment picture)?

I really appreciate the offer, but probably not that realistic/close enough. I'm in Dallas but the car is in somewhat rural East Texas (half hour outside of Tyler). This kind of junk on this car never seems to happen in Dallas near my garage/tools lol.

[yupetc]

Yep, that's the tool. And the N-series motor markings on the colored bars don't come with the kit. So you'll have to figure out which is which. And don't go off with what you see on the picture. Those can be wrong, at least on my car it's all mixed up badly. I used this kit on several N52, N54, and N55's. And the flywheel key is the weakest piece. Also, when you're about to set the flywheel key, it's best to remove the starter motor so you can get a better view of where the TDC hole is, because as you start to hand turn the crank, you'll need to have an estimation of where that flywheel's TDC hole is and having the starter out can help you "pre-see" as you turn the crank into it's TDC location.

Other things which may help:
1. Take your spark plugs out so the cylinders are open to the atmosphere that way when you turn the crank, you're not fighting against compressed air.

2. If you're taking the head out, you'll need to take the turbocharger off while the motor is in the car, it's best to remove the motor mount and have a transmission jack or something under the motor to help you elevate the motor. You'll have issues accessing some of the turbo bolts if you don't have a way to move the motor up and down for clearance.

There are probably other things to do, but this is all I vaguely recall for the moment.

3. Timing guides need to all come off first before you can work with the head bolt in the sprocket area. Or else, you'll have one bolt that the timing guide will block and you won't even see it.

[james92se]

Welp, just an update -

Put in another new thermostat and water pump this weekend, fresh coolant, re-bled it all.... and it promptly puked a bunch of coolant out of the expansion tank within the first 50 miles of driving.

Got the low coolant warning and then for the first time ever got a very brief high engine temp warning.

Still bizarre to me these cars have no coolant temp gauge but have an oil temperature gauge.

I won't be able to work on the car again now for two weeks so it's going to sit for a while.

Originally Posted by yupetc

Yep, that's the tool. And the N-series motor markings on the colored bars don't come with the kit. So you'll have to figure out which is which. And don't go off with what you see on the picture. Those can be wrong, at least on my car it's all mixed up badly. I used this kit on several N52, N54, and N55's. And the flywheel key is the weakest piece. Also, when you're about to set the flywheel key, it's best to remove the starter motor so you can get a better view of where the TDC hole is, because as you start to hand turn the crank, you'll need to have an estimation of where that flywheel's TDC hole is and having the starter out can help you "pre-see" as you turn the crank into it's TDC location.

Other things which may help:
1. Take your spark plugs out so the cylinders are open to the atmosphere that way when you turn the crank, you're not fighting against compressed air.

2. If you're taking the head out, you'll need to take the turbocharger off while the motor is in the car, it's best to remove the motor mount and have a transmission jack or something under the motor to help you elevate the motor. You'll have issues accessing some of the turbo bolts if you don't have a way to move the motor up and down for clearance.

There are probably other things to do, but this is all I vaguely recall for the moment.

3. Timing guides need to all come off first before you can work with the head bolt in the sprocket area. Or else, you'll have one bolt that the timing guide will block and you won't even see it.

Thanks - these are all helpful. Still odd to me that this head gasket very well might somewhat randomly have failed.

[yupetc]

Are you able to see where the coolant goes missing? If you're really having a coolant leaking into the combustion chamber, you should be able to locate a loss of compression in the associated cylinder. I've dealt with many a N55's, and this has to be one of those odd ones. Eager to find out, so please update.

[tfunk88]

Good luck! That’s a lotta work! Worth it to have it running like it should and be reliable, though

[james92se]

Originally Posted by yupetc

Are you able to see where the coolant goes missing? If you're really having a coolant leaking into the combustion chamber, you should be able to locate a loss of compression in the associated cylinder. I've dealt with many a N55's, and this has to be one of those odd ones. Eager to find out, so please update.

I haven't done a compression or leak down test on it yet. I have a compression tester but can't remember if I have a leak down tester. I'll have to dig through my toolboxes and check.

I have read that I need to get a thicker o-ring to use a compression tester on it though - this is why I initially put off doing a compression test earlier on as I didn't have much time to research or deal with that.

Any suggestions for sources of this thicker o-ring to swap onto my compression tester?

[yupetc]

Any "viton" material O-ring should do you justice for many uses ahead. Butyl O-rings will do but will deteoriate after few uses. Besides material selection, just get the ID and OD measured, and you're good to go.

[james92se]

Alright well an update here. I've been so busy I haven't had much time to mess with the X5.

I decided to run a different style combustion gas test on it - the kind that you stick the test strip down into the coolant tank and really have no worry about pulling in coolant to the tester like the cone shaped one with the liquid I originally used. The more I looked at the cone tester and watched the coolant tank with the lid off, I noticed there's a constant sputter of coolant into the tank from a little hole very high up on the coolant tank neck, which makes me wonder if despite my best efforts, the original chemical test was somehow being tainted with returning coolant?

Anyway, this style test indicated NO leakage even with a full 30+ minutes submerged in the coolant tank (stayed completely unchanged yellow color). To verify the strip actually worked at all, I then held it behind the tailpipe for a few minutes and it turned orange, as expected, with a for-sure carbon monoxide source.

So then I moved to a leak down and compression tests.

Leak down test produced nearly perfect results across the board (see pics). Took me a while to get good readings as I had to go find a fatter o-ring at O'Reilly's. Thankfully they had one in stock that worked (NBR o-ring #110, 3/8 inside, 9/16 outside, 3/32 thickness for anybody interested in the future). I also had to grind the adapter edges smoother as they were just wide enough to interfere with the plug wall and not screw down tight enough for a good seal.

Compression test:

Cylinder 1 - 205 PSI
Cylinder 2 - 228 PSI
Cylinder 3 - 227 PSI
Cylinder 4 - 221 PSI
Cylinder 5 - 223 PSI
Cylinder 6 - 224 PSI

Sooooo, cylinder 1 is lower, but not too low it is of concern in my experience and we're right there at the ~10% threshold between best and worst cylinder for a healthy engine rule of thumb. And again, the engine feels perfectly fine - no missing, no sputtering, no loss of power, and runs absolutely perfectly except for this stupid boiling coolant deal which effectively renders the car undriveable.

I would expect very obvious/bad leak down and/or compression numbers with a blown head gasket

Is perhaps the fan intermittently not working? Or not working well enough? I know the fan does work, because I see it, but it doesn't ever do that hard roar I'd expect from a fan in Texas summer. Is there a way I can test that, or test whatever it is that controls it?

If the fan wasn't bizarrely expensive I'd just replace it to rule it out for sure.

The only counter to the poorly working fan theory though is the AC blows ice cold even at idle, indicating good airflow across the condenser and obviously radiator too since it's sandwiched between the fan and condenser.

Any other ideas here? Any at-home diagnostics I can do with multimeter etc?

[Ascotgrun]

Are the heater hoses easily accessible?. I would try to clamp those to see if the heater core was leaking.

I would also try to sample the transmission fluid to see if the trans cooler has a leak and was allowing coolant to enter transmission circuit.

You are a far more patient man than I. I would have been looking to trade that sucker in a while ago.

[stocktree]

The little stream of coolant at the top of the tank is normal. Not sure how you think it would taint the test. And that is a lot more widely used and trusted test, vs your baggie test, that I've never seen before.
Hard to just say head gasket is ok, because the baggie test passed.
You can go into the hidden menu on the instrument cluster, and view your engine coolant temp, I thought. Same way you can go in and reset your service reminders.
If it's hot out and the ac is running, I'd imagine the fan would be spinning. Can you just pop the hood and look too see if it's turning?