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Gentlefolks,

Recently I found the coolant in my 2011 Focus mk3 seriously low. I also found traces of dried coolant in the vicinity of the reservoir tank. I started following what's going on more closely and found what to me looks like an odd behavior:

I top the reservoir tank to the max mark. Drive - quite a lot, in warm weather. Stop car, keep engine running, open bonnet: reservoir seems to not have lost a drop. Now, shut down engine. Within like 5-10 seconds, pressure builds up and fluid starts leaking; at least part of it seems to be from the release cap, not sure it's the only place. In a short while, there's a big puddle of coolant on the floor under the car.

Car cools down, process repeats. Fill fluid, drive (slow traffic, should be stressful enough for the cooling system). Nothing leaks. Park car, stop engine - psssffffssssffff. Puddle, lots of fluid pours out.

All of that time, temp gauge is rock solid at a hair below half.

No water in oil. No apparent oil in coolant.

Anyone seen this? What's going on?

Thanks for any insight.
 

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Thanks. How come?



Hard to say, it happens. It happened to me on my ‘13 MK3. I could smell coolant but see no visible leaks. Reserve tank kept loosing coolant over time. The car was still under the 3/36 so I took it into Ford & it was a faulty water pump.



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Discussion Starter #6
Hard to say, it happens. It happened to me on my ‘13 MK3. I could smell coolant but see no visible leaks. Reserve tank kept loosing coolant over time. The car was still under the 3/36 so I took it into Ford & it was a faulty water pump.
Got it. In my case the leak is extremely visible (and audible...) but happens only and exactly when I turn the engine off. I can drive for hours with the tank remaining topped without losing a drop. Then engine off - wait 5 sec - turbulence, tons of pressure into the tank and tons of fluid runs out, practically emptying the res tank.
 

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There is a weep hole for the water pump. Put a piece of cardboard under the car and wait. You should be able to zero in that way.
 

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If you can drive without issues, then In would say the pump is good.

One question, is the radiator fan working? Do you hear it running after parking and switching the engine off?
 

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Discussion Starter #9
If you can drive without issues, then In would say the pump is good.

One question, is the radiator fan working? Do you hear it running after parking and switching the engine off?
It does. It actually runs most of the time - which might also indicate something - but it sure does.

Is there anything in the cooling system - valve, thermostat, whatever - that opens up or releases when the engine is turned off?
 

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Change the cap so that issue is gone. Then look for other leaks.

The water pump can leak at the seal weep hole and yet still not overheat in use, you still change water pump to fix it.

Every car engine on the planet gets somewhat hotter when it shuts off, that is what is known to OEMs as a heat soak. The engine gets hotter for a bit as the water pump has quit turning. Any mechanical water temp gauge that still works with power off will show it, the engine say at 220 degrees water temp running then goes up for a few minutes to say 250, the pressure comes up too. Normal, the system has to put up with it with no leaks. The cooling has the coolant at slightly cooler than engine metal is, when it quits flowing then the engine metal evens the coolant temp up to exactly what it is. In normal use coolant say at 220 but engine metal at around 250 or higher, the oil temp, which is commonly higher than water temp. Engine temp will even be over that a bit, as the oil is a coolant of sorts too. They all work to even out as soon as engine stops, then engine metal acting as a heater for a bit until even then all cools down at the same time.
 

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Discussion Starter #11
Thanks for taking the time to write this, @amc49. That's extremely helpful (and educational) for me. Will post back when root cause found.
 

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Did you find out what the issue is? My 2014 Ford Focus se does the same exact thing. I can drive it for miles and everything is good. It doesn’t overheat, the fan comes on and off as expected but as soon as I pull in the driveway and turn it off, the coolant starts backing off in the reservoir and come out from the small overflow opening behind the reservoir cap. I changed the reservoir, flushed the radiator and changed the thermostat and the issue is still happening.
 

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I replaced the reservoir in my 2012 SE the past weekend. The bottom of the tank was slightly cracked, and it would leak consistently, especially when the hot car was turned off. As stated above, the heat soak of the hot engine will cause the coolant temperature and pressure to rise. This will stress the coolant system and any weak sections can and will break.
 

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That is what I thought was the issue initially and that is why the first thing I replaced was the coolant reservoir. As I mentioned I also changed the thermostat and flushed the radiator. But the problem persists.
 

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Last year I replaced the radiator on my '12. The crimp seam between the plastic sides and the aluminum core was leaking. I noticed coolant dripping from the radiator support beam under the engine bay.

Ultimately, you need to find the source of the leak. You will have to check all of the hoses, radiator, reservoir, reservoir cap, heater core, etc. A pressure tester will be very helpful, especially since you can then seek out the leak with the coolant being much, much cooler.
 

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Hi, there is no leak as I stated in my post. When I turn the car off, the coolant start flowing back into the coolant reservoir until it starts coming off the overflow opening near the cap. There is no leak anywhere.
 
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