Same thing happened to me
 

Wow...I was just skimming this thread because I recently just blew my 3.0i due to complete coolant loss and this is exactly the same thing that happened to me. My trans cooler popped off and I had no idea the coolant had dumped out and engine was overheating until the car starting idling rough at a stoplight before I got home and then died. I just barely made it home and it started knocking a bit as I pulled into the garage. I didn't realize the car was overheating because I was previously having issues with my coolant gauge pegging to the right on startup, and my in cabin heat was not working either. So when I was driving without heat on a very cold day (-25C) I expected it was the cold weather causing the issues with the rough running of the car. Unexpectedly as I popped the hood it was steaming and I realized the car had been overheating at that point.

The next day I discovered the coolant leak came from the trans cooler popping off because the clip was askew. I fully expect that this had happened upon me reinstalling the fan and shroud and accidentally knocking that clip for the trans cooler with the shroud. I'm surprised this isn't a common issue documented on this forum because it is SUPER easy to hit that clip with the fan shroud and knock it loose. Even when carefully re-installing the shroud I checked from beneath and saw I knocked it again. So note to anyone reading this, check your trans cooler clip each time you re-install the fan shroud.

Anyways, I poured coolant back into the system and ran it and noticed a leak from the coolant tubes under intake so I had replaced those because it basically disintegrated where it enters into the head. Once I replaced those the car ran fine for a couple of days and then developed a misfire on cyl 3 and 4, and started over pressurizing out of the expansion tank cap. It was at this point I realized that this was more than likely a head gasket failure.

This was about 2 days before I needed to leave for work and I'm not back until June of this year...so my wife just bought a beater car until I get back to replace the head gasket. We put the car up for sale thinking someone would buy it for 3k CAD as it's near perfect paint and body with zero rust but only a couple tire kickers. We've decided to keep the car as it really is comfortable and drives great and you can't get this much luxury in a used car for that price in the used car market anymore these days. I'll spend the time and money to just fix it myself so we can keep driving this thing...

I've come to same realization. I can put in a fully rebuilt n55 in my e70 for not half what best case scenario finding an equivalent replacement.

Make a thread for your HG job when you do it people will be very interested

Glad I’m not the only one who feels this way about their E53! Makes me feel a little less crazy. I’ve been on business travel the last few weeks so I haven’t had a chance to get back to work. Once I’m back and I get the E46 off its jacks I’ll get back to work on the X.

I don't think the compression test results make sense. I don't think you're getting the gauge to seal on those two. And when you put oil down in there there was some oil sitting on the metal ledge that helped the gauge seal. I would maybe try another gauge. Unplug the injectors and make sure you're holding the throttle down.

Dry v.s. wet the oil should help a few PSI if you have piston ring issues. Which you probably would have known if you had and you wouldn't have gotten from losing coolant.

If it's running okay and isn't smoking, it can't possibly have 30 PSI on two cylinders.

I've blown coolant on my b58 and m52 and both were fine after hitting the red. Maybe I'm just lucky but I think it's overstated. And I think people also overstate the head gasket job and many end up junked over a medium amount of work.

I saw that one on Craigslist too and really wanted to go get it. Mine doesn't have a roof and a tow hitch yet but if it did .. that was a good buy.

Well, I’m perplexed. Replaced the heater pipe and that took care of the last of the leaks. Then I reassembled the engine to get it to a running state.

First start. Idling a little lumpy. I let the engine continue up to operating temp, HVAC heater on high and fan on. Throughout the warmup, I got no hint of exhaust gas in the coolant. Once the thermostat opened up, a rush of gas came through until the coolant hit the tester in the filler neck. No change in the test fluid. Shut the engine off to avoid too much of a mess. Here’s some videos of the lumpy idle:

https://youtu.be/QnOdEsyxqm8?si=XqiDUoQtbQmMh01q

https://youtu.be/a6oymgFkHS0?si=Y94G3IWHkUffKYBy

Second start. Continued to sniff the coolant with heater open. Nothing. But this time the idle was silky smooth. I ran it until the thermostat opened and sent radiator fluid into the tester. There were some bubbles as it spilled out the filler neck. I haven’t done much with hot open cooling systems; I’m guessing the surge of coolant has more to do with it being hot and finding the path of least resistance.

https://youtu.be/vImaF5KG-ys?si=mi3WlzWhMwb6Kssh

Just to make sure, I took the tester to the tailpipe to make sure the fluid turned yellow sniffing straight exhaust and it did.
https://uploads.tapatalk-cdn.com/202...6bf5e032c9.jpg

So I’m confused. My gut feeling is that there has to be something wrong with this engine, but all tests seem to point to it being okay. What am I missing?

I hate coming across threads with no conclusion when I am searching for advice, so I’m here to put a long overdue pin in this.

Against all odds the M54 seems fine. After getting the engine running I sent an oil sample to Blackstone. They didn’t detect anything anomalous with the sample, just some slightly elevated bearing material compared to their average data (first sample I’ve sent out for this engine).

I’d estimate we’ve put between 500 and 1000 miles on the X5 so far after getting it running again. Coolant temps have been on the money, it runs well, and my main concern is back to the AC and some electrical gremlins.

Thanks to the forum for offering their insights here. Lesson learned to document symptoms better as they are happening (I.e., take a pic of the cluster if it overheats!)

Nice to see follow up.

Wife's engine hit the red very hard when her coolant reservoir blew. I had her drive less than three blocks to a parking lot where I could assess the damage. Temps were in the range of 240 ten minutes after shutdown but no bad mojo came of it.

Make threads for your other issues xo is the best place to DIY your X5!

I've driven n52 motor with non working coolant pump and n55 with an intermittent pump (these are both electric). Watching the temps all the time and they will go into warning like 240f and into engine will only idle about 250-255. I've had each of those hit the limit (for on the order of 1-2 minutes "in the red") and they survived. I think the m54 overheat program is engineered to save the motor and does the job.