Coolant boils off after 10 minutes of running

[DangerousDanGT3]

Last week noticed the fan in front of the radiator was activating more than normal and a couple of days ago noticed the coolant was a little low so topped it up but as soon as I started the engine it drank it all there is no leakage on the floor no smoke out of the exhaust and the temp gauge does change nor does the car run any different.
Took it into the garage yesterday and they said they couldn’t find any leak and that the coolant is just boiling off. Their summery is that it could be anything from a failed water pump to a blown head gasket and the only way to find out is to strip the engine down. Has anyone else had any issues like this and if so what was the cause? Hoping it’s something small and not disastrous

 

[scooter123]

More information is needed. Year and mileage is a good starting point. In addition any Mods is also helpful. I will also note that removing the spark plugs and looking at the piston tops with a borescope will also provide an indication of a Head Gasket leak into the combustion chamber. Because coolant in the combustion chamber will result in an exceptionally clean piston tops. Finally water pumps will typically fail at the shaft seal and leave a coolant trail below that point and will typically produce a puddle of coolant on the ground under the "front" of the engine.

 

[slopoke]

Did you pull the dipstick and pull the oil filler cap and look at it's underside for milky oil? If the coolant level is still low, refill it and squeeze, release and repeat to the lower radiator hose to make sure that there isn't an air bubble in it. Do the same with the other coolant lines. Did the coolant level drop again after refill? If it did, I'd add more coolant, bring it up to full operating temps and let it cool overnite to see if the coolant level dropped again. Check around the turbo, it's cooled by the same coolant as the engine. Good luck.

 

[DangerousDanGT3]

Sorry thought I’d put down what year it was 🤦🏼‍♂️ 2014 with 77,000 miles it’s had a stage 1 remap, induction kit, exhaust upgrade and the car was bought with everything done to it not me personally sorry if that’s not much help and it doesn’t sound very promising

 

[DangerousDanGT3]

Yeah I checked the oil cap and dipstick and everything was normal checked the coolant reservoir for any funny smells but there seems to be nothing out of the ordinary and as for the coolant level at first I filled it up and it just drained when I started the engine so I refilled it again and it stayed in between the max and min line but as soon as you start getting the engine warm the coolant starts boiling.

 

[M-Sport fan]

Possibly a stuck closed/clogged thermostat, or one of the coolant valves is totally defective??

Is our overflow tank part of the main block coolant circulation during cold start/open loop warm up, or is it only accessed after full warm up, and closed loop engine operation?

 

[DangerousDanGT3]

I wouldn’t know but it has made me feel a lot more positive about the outcome I’ll update with my findings when I can 👍

 

[Dialcaliper]

I wouldn’t know but it has made me feel a lot more positive about the outcome I’ll update with my findings when I can 👍

Do a pressure and vacuum test on the coolant system. A shop can do it, or you might be able to buy or rent a vacuum fill kit and pressure pump.

When you charged the system, did you vacuum fill, or just pour in coolant and run the engine to bleed? If the latter, it’s possible you’ve got trapped air, especially in the heater core, and it’s slowly burping out. Bleed the top of the radiator again (while cold, into a cup is fine) and keep adding coolant. As long as you’re not overheating, you might be okay and it might stop after a while.

You should be able to charge 21psi and vacuum to 20” Hg, and the system will hold it there for 20-30. If it doesn’t and your adapter is sealing properly you’ve probably got a leak somewhere.

The low side tank is hooked up all the time, the low side via the thermostat housing (T to the oil cooler line, and also the return line from the turbo).

How many times have you topped it off, and do you have stock or silicone radiator hoses? Silicone hoses are great at holding pressure, but long term are slowly permeable to water vapor. I replaced just about everything (radiator and all “ancillary” hoses) with silicone and even with a well sealed system that holds pressure, I need to top up the reservoir (from low to high) every 3-4 months (fortunately I knew about it going in or it would be slowly driving me mad)

 

[green_henry]

Running the heater full blast might help. Wouldn't hurt.

 

[scooter123]

Can you actually see the coolant boiling in the reservoir or is this an assumption that it's happening within the engine. Thought here is that if you are seeing bubbles in the reservoir that may be an indication of a large airspace in your radiator or engine block. If that is the case a Vacuum fill of the cooling system is the solution.

 

[DangerousDanGT3]

@Dialcaliper I poured the coolant in and ran the engine and I’ve filled it up 3 times on the third time it didn’t disappear that’s when I got it to the garage and they’ve had it up couldn’t see a leak but was advised it’d be ok to drive back to my house (had issues with people smashing cars in the area) and have been driving it back to the garage for work but the problem has seemed to disappear no more overheating or coolant loss so spoke to the main guy at the garage this morning and he’s thinking the fan on the back of the water pump has been acting up and has probably come away which is allowing the coolant to flow freely for now. Hopefully it is the fan so should be an easy fix. 🤞🏻

@green_henry i would but the blower motor has stopped working so that’s something else they were sorting.

@scooter123 i saw air coming into the coolant could of been boiling but wasn’t sure but the guy who was looking for the leak at the garage said he had the car at 2k rpm for 10 mins and all the coolant had boiled from the header tank.

 

[M-Sport fan]

spoke to the main guy at the garage this morning and he’s thinking the fan on the back of the water pump has been acting up and has probably come away which is allowing the coolant to flow freely for now. Hopefully it is the fan so should be an easy fix. 🤞🏻

Are you referring to the IMPELLER in the water pump housing??

IF so, then you must replace the whole water pump which yes, is an 'easy fix' per se, albeit not an inexpensive one if someone else is doing the labor.

In any case, there will be no coolant circulation without that impeller attached to the WP shaft and functional, and if that is the scenario, the car WILL overheat and blow the head gasket/warp cylinder head/etc.

 

[DangerousDanGT3]

I honestly don’t know all I was told was that sometime the fan on the back of the water pump can split which causes intermittent cooling issues and then when it comes off completely the coolant works like normal again I’m not clued up on things like that so not 100% sure I’m explaining it right but for now the coolant is working like it’s supposed to the engine isn’t overheating and when you look at the header tank you can see the coolant coming back in where as before they looked at it there wasn’t any flow.

 

[M-Sport fan]

Now I have to look at the design of our OEM water pump, because that sounds strange.
But then so is having so many extraneous valves and flow controls on a cooling system, like we have on ours, so our water pump's impeller/internal design could be equally strange.

Unless the shop dude was speaking to a stuck closed/clogged thermostat which worked it's way to (default) wide open??

 

[DangerousDanGT3]

That’s a possibility I did mention that to them so when it goes in I’ll get em to check that first 👍

 

[scooter123]

In all this thread I've only seen indications that the temperature indicator is reading "normal". On some cars if the coolant level is low enough the only indicator is no heat, the temperature sensor will be bone dry and only report a false reading. My experience is that is NOT the case with the Fiesta, you should be reading an overheat condition. However that overheat condition will disappear as soon as you shut the engine off.

I will also note that for nearly 90 years the highest point in the cooling system was the radiator cap on the top of the radiator. When that was the case all you had to do to clear an air pocket was put the front tires on some ramps and remove the radiator cap. Then you could fill the radiator to the top with confidence the cooling system was full. Today many cars don't have a radiator cap, they have a remote coolant tank and require vacuum filling if the coolant tank has been emptied. Pouring more coolant in the reservoir won't do a thinking for that giant air bubble in the radiator. I'll also note that the Helm Service Manual for the Fiesta ST has a distinct post vacuum fill procedure for working any small air pockets out of the Cooling system.

I strongly suggest that you ask your mechanic if he has done a vacuum fill on this car and if he actually used a vacuum fill system to do it. I also have a vague memory of Ford having issues with leaking coolant reservoirs with the 2014-15 cars. It may be wise if you can scout around and find a 2016 and later reservoir to swap out.

 

[DangerousDanGT3]

I shall ask them tomorrow about the vacuum filling and that’s the weird thing about this situation that the engine is clearly overheating as the cooling fan was on high and stayed on for a few minutes after I’d switched the engine off but the temp gauge read normal to the point of rising normally to normal temperature 🤦🏼‍♂️

 

[DangerousDanGT3]

Also I can’t thank everyone who has given their time ideas and advice again thank you so much

 

[DangerousDanGT3]

**UPDATE**
Since the garage boiled off the coolant looking for the a leak everything has gone back to normal they believe that it was an air lock so luckily I didn’t end up having the engine stripped for no reason fingers crossed they are right 🤞🏻