Boiling expansion tank?
 

I got out of my car the other night hearing a boiling under the hood, I raised the hood and found the Radiator expansion tank full and boiling inside.:confused:
I left the hood up and let it cool down until the morning. When I went out the next day and checked the tank, it was virtually empty. My question is, is that normal? I got my 07 MCS not to long ago and I am getting familiar with the systems, but that one concerned me as I didn't get an indicator light or notice letting me know it was hot and I just came off the highway of a lengthy drive at 70-80 mph.
Can anyone guide me to a resolution?

Thanks

Richard

Your car overheated or there is a leak somewhere in the cooling system or both. You need a way to see coolant temperature to start diagnosing. Easiest way is probably a Bluetooth OBD-II module and the torque Android app. Also spend some time trying to figure out where the coolant leaked from

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Thanks, what are normal temps for the MCS?

Do some searching on thermostat failures and you'll turn up lots of threads. I believe the S/JCW models are supposed to run at 220F

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I have an ultragauge & it indicates coolant temps of 219 on regular driving, drive harder & temps go down to 190

Maybe you got not cooling warning light because a) the sensor is faulty or b) you have very little coolant relative to water in your tank. 220 degrees for water would be boiling, for coolant it is normal for our cars. Get a scanguage and start diagnosing.

The reason coolant doesn't boil normally is because it's kept under pressure. Race cars run 100% water on the track and they don't boil coolant.

My first guess would be a failed thermostat. We had a similar issue on our mini.

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Thanks for the feedback, I am searching for a compatible odb-2 for an Iphone, at this point i wish I had an Android from what I am seeing. Oh well, I will get fixed up and monitor what is happening and update here.

Thanks again.

Richard

First, fill up the tank and see if there is a leak. The coolant is blue. If the thermostat is leaking, there will be some liquid on top of the transmission. Get a flashlight and look on the driver side of the engine, under the intake tube and see if there is any trace of coolant there.

The water pump is on the passenger side of the engine, near the back.

Use BMW/MINI coolant and distilled water. There are threads here on how to bleed the system (thermostat replacement). Take a couple of short trips, allowing the car to cool down, and keep topping off the coolant tank.

You need to determine where the coolant is going. Keep the coolant tank full until you can get the leak fixed. Really bad things can happen if the engine runs dry.

Mike

You may want to check out the Ultra Gauge. It's one of the least expensive and easiest ways to monitor coolant temps. I installed one in my '07 Justa about two months ago and I am very satisfied so far. On normal driving coolant temp settles in at 222.8 degrees.

OK, I got home this evening and have been studying my cooling system as well as read the bentley manual regarding draining and refilling the cooling system on my N-14 engine. First, I haven't found any obvious leaking so far, but what I did find and it kind of concerns me is; in the bottom of the expansion tank, it appears to have a green color to the antifreeze....... SO, I am going to take a guess that the dealer (Not MINI) I bought my MCS from topped it off with regular green antifreeze, therefore, I need to get it out, flush it and install a fresh batch of Blue antifreeze and start over hoping that there isn't a mix or anything it has caused. My question is, the Manual says to separate the hose along the bottom of the radiator and letting it drain out, BUT I had also read in a post here where there was a block drain on the back of the engine? They didn't specify which engine model it was and may not involve the N-14. I am just wanting to make sure I am doing it right and I know you experts would know. I am planning on flushing by putting a hose in one end of the separated hose and flushing until it is flowing out of the other end, filling with water, running it a little bit then draining, filling it back up with 50/50 blue antifreeze unless advised otherwise here.
I also got DashCommand downloaded and have a WIFI OBD2 scanner coming for my iPhone to monitor the temps moving forward.
Thanks in advance for any guidance or feedback.

Richard

Hello Richard,
I had the exact same issue not too long ago.
After it passed 2 system pressure tests at my MINI dealer, they were baffled.
I asked them if/how they tested the cap and he laughed.
"They remove the cap to test the system".

He then gave me a new cap and I was on my way.
It hasn't happened since.
It still makes my chuckle that I lost 2 days on this...

I'd recommend to start at the coolant reservoir cap.
I hope this helps.

I think you're over complicating it. Drain it by simply splitting the hoses at the bottom of the radiator. Fill from the top with new. all that flushing is probably unnecessary. I thought blue and green coolant mixed just fine. If you haven't found any leaks my bet is on the thermostat. We just went through a very similar issue. Car was fine driving on the street but would overheat after a few auto-x runs and start spitting coolant. Dealer replaced the entire cooling system before finally fixing it with a new thermostat.

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Thanks, I know I was overthinking it, but I didn't know that the green and Blue antifreeze was compatible and I wanted to make sure I flushed it well. I will drain and refill and start from there.

Richard

You may want to check into the whole blue vs green coolant question further. Plenty has already been posted on NAM on this subject and from what I've read they are not compatible. Good luck.

the blue and green antifreeze are both ethylene glycol, so will be compatible. the blue is a lower silicate formula that will reduce buildup. Make sure that you use distilled water, tap water has a bunch of minerals that can buildup on metal surfaces. Chances are that you will be draining your system twice (once to fill and check, and once after the repair). If you replace the drained coolant with new, and distilled water, then you should have almost all of the green additives out of your system. I would not be worried.

Have fun,
Mike

Thanks, I will be working on it tonight..

Richard

Good advice mbwicz : check for leaks at the most common places. Here is a link to the thread where the locations and picture of the parts. Recommend the MINI blue coolant and mix 50/ 50 with distilled water , flush the old stuff out.

https://www.northamericanmotoring.co...t-leak-or.html

Good luck.

I understand my capacity is 1.4 gallons at a 50/50 mix, but during my flushing, I was only able to put back 3/4 - 1 gallon of fluid each time I flushed the system. During each flush, I burped the system with the bleeder and ran it for a while to try to get it circulated per the instructions, but still only yielded the same amount. I would figure that the heater core holds some of it as it probably doesn't drain it, so I have a two part question for the experts please.
Does the heater core account for 1/2 gallon +/-? and since I have flushed my system 3 times and have only distilled water in the system, if I use a 50/50 mix and the heater core holds 1/2 gallon, should I mix the coolant thicker to compensate?

Thanks for the feedback

Richard

Yes, I would add straight coolant first. The engine block does not drain, and the heater core will retain some as well.

If the system is 1.4 gallons total, and the coolant is coming out nearly clear, then I would assume that all of the coolant is removed. I would at least 1/2 gallon of straight coolant, up to about .7 gallons. The coolant will mix with the water as the engine runs. Then I would top off the coolant tank after bleeding with 50/50 mix. Even though you don't have to worry about freezing in Houston, you are still better off having a little extra coolant concentration than too little.

Have fun,
Mike

As luck would have it, my expansion tank was what was leaking LoL, changed it out and now seems to stay at the same level and the tank doesn't hiss.
Thanks
One more question though. I am using DashCommand and my temps are running 222-236 on highway and 220 at idle, I tried the sport theory, but that didn't work.
Are those temps still within limits not to cause problems?

Thread resurrection.
 

Hi everyone, first post by me, been lurking for awhile and appreciate learning from your experiences with the MC. I have a 2011 MCS that had a small leak at the thermostat housing to the heater core, I replaced the thermostat with OEM parts (first one failed immediately, second one working great). My problem is that immediately after this repair I have pressure building and being released by the expansion tank and cap after I shut the car down. My temps never exceed 105 C drop to about 99C when driving spiritedly, thermostat opens at 103C, fans work and will run for about one minute after shutdown, heat is very good in the cabin. Coolant level just under the max line when cool or running and will rise to the top after a minute of not running after fully warmed up. The coolant will bleed out around the cap while hissing and dissipating pressure over the next 5 minutes. I replaced the expansion tank cap and this did not change anything. I can see no visible leaks from the expansion tank, I did not have leaks before the repair except from the thermostat housing.
Question is this: The new cap is bad, the expansion tank suddenly leaks, there is still air in the system that I can't bleed out? What do you think? Thanks.

Bleed it like crazy first, mine took a couple of times of hot to cold cycles.

https://www.northamericanmotoring.co...-question.html

Also, did you hook up the hose after the repair just that like the factory, one mis hooked up hose in the system and you can have overflow issues.

https://www.northamericanmotoring.co...hermostat.html

I appreciate this timely response, hoses are all correct as the coolant flow while running is good and temperature is stable and well controlled by the thermostat. I have bled the system 3 times and cannot guarantee it is not still having air in the system, but the heat works great, the coolant level while running stays put, its just after shutdown that the pressure builds. I'll bleed it again.

I think you got your hoses mixed up. It's not flowing in the correct direction.