Cooling problem, I'm stumped!

[Bmwe5320023.0]

In the past few weeks/months, I've been getting a low coolant message. I drive the vehicle very little for the most part, so I was just adding coolant every few weeks.
Yes at the same time, I've taken the vehicle on 500km trips, so i know for sure the leak wasnt too bad, or i wouldn't have made it without adding coolant during the trip, which i did not do.

The vehicle wasn't overheating, and I didn't see any leaks, so I thought maybe the engine is taking a little hit of coolant.

But 2 days ago I had my X5 2002 3.0 (M54) overheat badly.
I traced the problem to the lower radiator hose, because I could see the coolant leaking from there.

The factory clamp of the lower hose came partially off, and the coolant was leaking so bad I went through 5 gallons of coolant in 10 minutes.
Luckily I found a Napa store nearby, and put a clamp on top, which allowed me to get home. With a pit spot in between, to cool off and add more coolant to the system.

At home I removed the factory clamps, and installed my own clamps.
No more leaks.
I thought I was done with what was an easy fix.

No quite....

As soon as I started driving it kept overhearing again, and the coolant was going somewhere, disappearing.
I checked, no coolant in the oil, no smoke from the pipe, nothing leaking from under the car.

I bled the system, even parked it at a steep angle, and set the heater on 32C degrees and lowest fan setting.

I noticed something happened with the red floating level in the expansion tank. Somehow it came out of its orbit, so it wasn't centered. But then it disappeared completely, even when the expansion tank is full.
It must've stuck somewhere.

I'm really stumped by this we I've fully replace the coolant system within last 15k km

The other thing that happened when X5 overheated a couple of days ago, the active cruise control light came on the dash and is still there lol

All the hoses are hot to the touch, so I assume the coolant is making its way through the radiator, which means that the thermostat is good then?

I really don't understand where the coolant keeps disappearing. On a 30 minute drive, I have to stop 3 times to cool off the vehicle, open the expansion cap, and add a good few liters of coolant.

I have 1.4 bar cap from E34, which means the system will vent sooner if it overheats.
Never had any problems because of it before, neither with E39 not 53.

I can't figure out where the coolant is disappearing and why I can't drive the vehicle for more than 10 minutes without overhearing.

I'm watching the temperature live, and it just keeps going up until 125 where it just gives a massive warning. I try to turn off the vehicle before that and cool it off.

This is just driving me nuts

[andrewwynn]

Loss of coolant without steam is not good but with low pressure cap you may be venting without realizing.

A recent m54 very similar situation was from the pump impeller failing. It will break free from the axle and not spin. No flow= overheat. Overheat over pressure vent through low pressure cap.

Hopefully that's your issue else it could be the head gasket but you should see lots of white smoke if that's the case.

I'm not sure the easiest way to diagnose. I forget if the pump has houses out front but you may be able to confirm the impeller is intact or not though the hose goesin or goesout without having to remove the pump itself (but of course draining enough coolant).

Good luck.

[Bmwe5320023.0]

But I drove for many many months with this cap without issues. I don't understand. Lots of people convert to this cap and I haven't seen anyone report any issues.
In fact GAS made 1.2 bar cap and countless people used it without any issues.

As for the impeller, I have a metal one, so it shouldn't break but who knows!

Out of desperation I purchased a thermostat from the dealer today, but I don't think it's the thermostat.
If the thermostat was stuck closed, the coolant wouldn't make it to the lower and upper hoses right?

[andrewwynn]

Cap unrelated to failure and possibly helpful in that it will cause an obvious fault at a lower pressure then will cause damage to the reservoir and other plastic parts is my understanding of why people do it.

I don't remember what the path of the coolant when tstat is stuck closed but I wouldn't be too surprised if tstat opens enough to get some water though too radiator.

Metal impeller is good but if the impeller broke free from the axle it won't push wate also "hot" is very relative if you didn't actually measure the temps and just put hand on them.

[getty150]

I've had somewhat of a similar experience with my 05. X3 m54.
The problem...the fan would not kick on. Now the fan functioned fine on another X3. But not on mine. Using the scanner I cleared the fault code , and wouldn't you know it the fan kicked on. And no more temp arm traveling to the red.


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[Bmwe5320023.0]

I bled the system as much as I can and drove home 30 minutes. The temperature was very slowly creeping up.
When I stop, the temperature does drop. There's lots of steam coming from under the hood and wheel well, temperature is about 110-120 Celsius.
Just as my trip was about over, 30min or about 50 km, I got the message of low coolant displayed on the dash.
I dont get it what's happening with the coolant lol, is it evaporating, and why?

[Bmwe5320023.0]

So far the theories are either a partially stuck open thermostat, or broken water pump?

I replaced the Auxiliary Fan last year, so it should be working. In either case, I don't think the aux fan works when the vehicle is driving. Clutch fan and speed is normally enough. So as far as I know it only kicks in when stationary.

[EODguy]

Webasto connector plug/hose leak? Even without a Webasto it still has the connector (plug/hose) for it....


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[Bmwe5320023.0]

I dont know where the webasto hose would be, but if anything is leaking at this rate, I would expect to see the leak on the ground with the vehicle running, but i don't see a leak. I want to see a leak! Then I can trace it. For now no leak, just disappearing coolant.
I think soon I will just be filling it with tap water, I spent $100 on coolant in 2 days

[Bmwe5320023.0]

The only other idea I have is the 2 pipes under the intake manifold. But I have replaced them.
Maybe they're leaking the coolant on the engine, which then evaporates. But I would expect the smoke to be coming from there, instead it's coming from the coolant reservoir area...