Coolant Leak/Boiling/Steaming

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New here! Will say right off the bat car knowledge isn't my strongest suit but i've been trying to tackle my latest problem. I've got a 2004 Ford Fusion.

About a week ago when parking up i noticed a puddle under my car (under the driver foot well it seemed to be coming from). Enough liquid to start trickling down the street. After looking under the hood i noticed my coolant tank was now near empty. So i re-filled it, with a coolant/distilled water mix and made my journey back. On the journey back i noticed a little bit of stream coming from under my bonnet and when i got home i realised my coolant tank was nearly empty again.

I re-filled it and sat on my drive revving my car, trying to heat it up and i noticed that my coolant tank was boiling, whistling, giving off steam and sure enough after a point water/coolant started spluttering out of the cap area. I thought it might be a dud cap so i bought a replacement one.

After replacing that i decided to re-fill it and make the short half mile trip to the petrol station to test it, i noticed some steam again, and this time i felt like i could HEAR bubbling coming from the tank. I also felt like the power steering got heavy turning corners, not sure how/if thats related but has never happened before. Sure enough when i got back the coolant tank was completely EMPTY again.

I've checked my oil, there is no milky white coloration in the oil etc. There is no oil in the coolant tank either. I am wondering if replacing the actual coolant tank is the next step. It holds liquid absolutely fine when the engine is off, level doesn't deplete so wondering if its an expansion issue.

Any suggestions/diagnosis would be greatly appreciated as like i said, relatively clueless when it comes to this stuff.

Thanks guys.

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I ain’t no mechanic, but nosing about on this website you can pick up a few handy tips... however don’t quote me on this...


if you are 100% sure the coolant isn’t leaking, its a possibility your serpentine belt maybe broke, causing issues with your coolant/power steering and further mechanical issues.

The belt isn’t often covered and decently easy to find, have a snoop at the engine to see if you can see the remains or where the belt would sit.


im sure someone out here can correct me if I’m wrong or identify the issue better.

either way best of luck 

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Lots of shiny rollers and pulleys without anything on them would be a clue to a broken belt but the alternator light would be on and the steering very heavy. If it is, there may be a tension issue if the belt is visibly ok. Could be serious or fairly trivial. The coolant has boiled away and you have replaced a suspect cap. Has the system been bled?. Expanding air locks stop the water from circulating, it boils in the hot spots and hides the potentially cured fault. Ignoring the head gasket which is the worst case but least likely scenario for a minute, several things can cause this. Busted tensioner on the belt. Next, thermostat not opening, Radiator blocked, water pump not working.  Work logically through these checking each one (do some reading.)

My tip for bleeding is to firmly fit a 2 litre plastic bottle with the bottom cut off into the filler opening. Fill it with water and keep doing so with the engine running and the heater on full. If it stops bubbling up,(this could well take twenty minutes,)

then the system is full and bled because the head of water allows the system to bleed and refill the system at the same time. If it doesn't there is no circulation somewhere. Check both the top and bottom hoses from the radiator. The top one will be hotter than the bottom but if the bottom one does not get hot at all, suspect blocked thermostat or radiator. If it only gets a bit warm, suspect the water pump or again the thermostat..

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