N54 Coolant Tank Exploding / Car Overheating

[RestoreItSteve]

Hey guys, I'm kind of new to the forum and the N54, so nice to meet you all!

I've had my 1M for about a year now. I was driving on the motorway the other day when the car went into limp mode and wanted me to stop to let it cool down.

I did so immediately and then lifted the bonnet to find coolant sprayed everywhere from I think the top of the expansion tank.

I let it cool down, opened the expansion tank, and topped it up with distilled water (all I had on me). The car was cool and so I continued my trip to London. The car was then parked for two days.

As I was 30 minutes into my return trip the car went back into limp mode and overheated. I again pulled over, let it cool down, topped it up, and drove home.

Both times it overheated I could see coolant leaking at the front right of the engine bay, just reaching the front right wheel. In hindsight, this could be from the scuttle panel moving it from somewhere else. And also, from the overflow hole that's under the cap on the expansion tank.

I've had the car on my ramp and the scuttle removed but I can't seem to find the leak. The expansion tank is fine, I put it underwater to check for leaks. The radiator isn't leaking, I've had the intercooler off to get a good look.

I didn't get any low coolant warnings and I can't see any drips when I let the car heat up in the workshop.

The service light has recently come on, so I have new spark plugs, and a pollen filter to do... I always do the oil and filter every 6000 miles, but do I need to do the coolant? Could the explosion of coolant be caused by old coolant not doing its job anymore? I have some BMW coolant coming tomorrow and will do a full change. But I'm worried something else is wrong and I don't really have any idea.

I've looked at a few YT videos and checked the usual places and pipes but everything seems good. The car is on 75k miles. It's left-hand drive and has been problem-free the whole time.

I'm used to working on E30's which are basic in comparison. Any help is appreciated. Cheers, Steve.

[08SlowE82]

Maybe the cap was not venting and this is caused by an over psi issue. Would recommend replacing the tank. And do an inspection of the entire cooling circuit with coolant flush while your in there. The bleeding procedure can be found on here or YouTube university😎

[Jonah335]

If the tank isn't cracked and you don't see any obvious leaks, try a new bleeder screw. I've seen a few fail.

[zx10guy]

I'd just go ahead and replace the tank. Mine was spraying coolant in a similar fashion as yours. Got a replacement tank from FCP Euro which included a new cap, bleeder screw, and low coolant sensor. After installing the new tank, no more coolant spray.

These tanks are known to fail due to them being plastic.

[RestoreItSteve]

Thanks for the advice guys! Appreciate it.

[dtla1]

Any chance it could be a failing/failed Water Pump and/or Thermostat?

[RestoreItSteve]

Well interestingly, I can't get the water pump to activate after doing the coolant bleed initiation procedure which involves one press of the ignition button and holding my foot on the throttle pedal for ten seconds. Nothing happens... perhaps it is the water pump.

Once the engine is on, water does come from the feed pipe that runs across the rad.

Does anyone know if the water pump is engine-driven as well, or is it just electric? I think it's odd that I can't get it to work with the engine off.

[schmidtp]

Water pump is electric and known to fail. Many people replace as preventative since it can leave you stranded. I had one even crack the plastic housing and leak everywhere.

[dtla1]

Originally Posted by RestoreItSteve

Well interestingly, I can't get the water pump to activate after doing the coolant bleed initiation procedure which involves one press of the ignition button and holding my foot on the throttle pedal for ten seconds. Nothing happens... perhaps it is the water pump.

Once the engine is on, water does come from the feed pipe that runs across the rad.

Does anyone know if the water pump is engine-driven as well, or is it just electric? I think it's odd that I can't get it to work with the engine off.

You also need to set the temp to something, and fan speed to something specific. Sorry I don't remember exactly, but it's around here or a video on youtube.

[RestoreItSteve]

Thanks, guys. I saw the vids. I'll try the process again but I'm sure I had it on hot and the lowest fan settings. If it really won't work I'll assume it's the water pump.

Does anything else circulate coolant? Because like I said I saw it being pumped into the expansion tank, but only when the engine was running.

Cheers

[TWO STEP TEX]

I agree, it's most likely the WP since it's a know failure item, but it may also be the thermostat. Sounds like the coolant is getting hot enough to boil so it's either not getting circulated from the pump or the thermostat.