ifloochies

Coolant boiling in expansion tank - 1.6 Sigma NA

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Hi there.
Hoping I can get some help with this issue that I'm having with my 2011 Fiesta SE with the 1.6 NA engine.
So as title states, from startup and idling for about 8 to 10 minutes, the coolant in the expansion tank would rise all the way up and start to boil within the expansion tank.
At this point, the top radiator hose would be hot to the touch, but the bottom hose would be just slightly warm.
The fan would then kick in, and stay on for a few minutes even after the engine has been shut off.

So what I've done so far...
Replaced thermostat twice.
Replaced expansion tank cap.
Pressure tested the cooling system and found that it would hold pressure, so doesn't look like I have any leaks.

Bled the system countless times.

Only thing I haven't replaced is the radiator. 
Any advice, because this is really starting to do my head in.

Thanks in advance. 

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Don't know if you can do it with radiators nowadays but way way back you you could take bottom and top hoses off stick a garden hose in bottom of rad where the pipe hoses connect and back flush the crud out. Sounds like a blockage somewhere. Cheaper to try that first before buying a new rad. 

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Hi auldreekie,

Thanks for your response.

So you think its worth taking a look at flow through the radiator, or rather the lack of it.

At this point I'm open to trying anything.

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The top hose being hot and bottom one cool blockage in the rad or worse in the engine itself. 

Myself I'd probably buy a bottle of radiator flush about a fiver in ECP, don't know halfrauds price. Empty the radiator, put the flush in as per instruction on the bottle. top up with water and run engine as instructed. 

Empty it again then back flush with garden hose making sure water coming out is clear and free flowing. You might need to take thermostat back out. 

If all OK then reconnect rad hoses, I think I'd drive car for a week to make sure all is well, you'll need to replenish antifreeze before winter. 

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Will certainly give that a go and report back.

Thanks once again.

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Does the top radiator hose get solid as well as hot?  If so, I'd recommend a sniff test to check for exhaust gasses in the coolant.

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35 minutes ago, TomsFocus said:

Does the top radiator hose get solid as well as hot?  If so, I'd recommend a sniff test to check for exhaust gasses in the coolant.

No, on the contrary the hose doesn't get hard at all, just very hot to the touch.

Opening the bleed point at the top of the radiator releases scalding hot coolant, whiles the core of the radiator remains relatively cool to the touch.

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Just now, ifloochies said:

No, on the contrary the hose doesn't get hard at all, just very hot to the touch.

Opening the bleed point at the top of the radiator releases scalding hot coolant, whiles the core of the radiator remains relatively cool to the touch.

Ok, we can rule out head gasket then. :smile:  

Waterpump is another possibility though, if the coolant isn't circulating properly it will over heat at the top end quickly.  I can't remember the last time I had to flush a radiator, they don't block up like they used to unless people use the wrong coolant or stick something like K-Seal into the system.  Do your heaters work ok or are they pretty cool?

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On 7/21/2019 at 12:53 PM, TomsFocus said:

Ok, we can rule out head gasket then. :smile:  

Waterpump is another possibility though, if the coolant isn't circulating properly it will over heat at the top end quickly.  I can't remember the last time I had to flush a radiator, they don't block up like they used to unless people use the wrong coolant or stick something like K-Seal into the system.  Do your heaters work ok or are they pretty cool?

Certainly not the water pump.

The time I had the alternator off to replace the thermostat, I had water push out of the thermostat opening just by spinning the water pump pulley briskly by hand.

Incidentally I took the radiator off today and tried blowing through the inlet, and even though I could blow through the other end/outlet, it did require some effort.

Dont know what could be restricting flow through it if any at all, I'll have it cleaned out, reinstall and report back.

 

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Alas, still no joy.

Had the radiator cleaned out - able to blow through it end to end with ease now.

Installed it and still have the coolant boiling in the expansion tank.

For some reason it looks like the coolant is bypassing the radiator, because the bottom hose barely gets warm.

An observation I made is, keeping the revs at 2500, the temperature would slowly creep up as normal, reach the temperature at which the fan kicks in at 105 degrees C, cool back down to 99 degrees C where the fan goes off as normal.

By doing this, the bottom hose does get just as hot as the top hose, as well as the entire surface of the radiator.

Properly stumped now.

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20 hours ago, ifloochies said:

Alas, still no joy.

Had the radiator cleaned out - able to blow through it end to end with ease now.

Installed it and still have the coolant boiling in the expansion tank.

For some reason it looks like the coolant is bypassing the radiator, because the bottom hose barely gets warm.

An observation I made is, keeping the revs at 2500, the temperature would slowly creep up as normal, reach the temperature at which the fan kicks in at 105 degrees C, cool back down to 99 degrees C where the fan goes off as normal.

By doing this, the bottom hose does get just as hot as the top hose, as well as the entire surface of the radiator.

Properly stumped now.

 

The boiling point of water is 100c, if your fan isnt kicking in till 105 then thats an issue right there?

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48 minutes ago, Martin-Fiesta-MK6-1.4 said:

The boiling point of water is 100c, if your fan isnt kicking in till 105 then thats an issue right there?

It's 100 at atmospheric pressure.

A car's coolant system is (supposed to be) pressurised, which means it raises the temp at which the fluid will boil.

Which could also mean there is a pressure leak somewhere, allowing the coolant to boil at a "lower" temperature than it otherwise should, if it's boiling at 100.

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Still sounds like the waterpump to me.  It's not working efficiently enough until you raise the revs.  Water coming out of the stat hole doesn't test the flow rate, just that it is able to push some water around.

Are you 100% sure the reservoir and cap are both good?  It usually is one of those at fault when the coolant boils.  The reservoirs get tiny hairline cracks that open up more in the heat so can pass a cold pressure test.  And were the caps genuine?  

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If I'm to consider the water pump, are these the kind with a plastic impeller that falls off with age?

The caps, I bought off amazon.

I have any coolant reservoir from a working vehicle I can swap out with.

Whiles I take time out to work on it again, is there anything else I ought to look out for?

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amazon sell both genuine and aftermarket caps.  If you check your invoice it should show whether it's genuine or not.  The non genuine ones don't usually work to the same tolerance in my experience.

If you can swap the reservoir and cap from the working vehicle that would be a useful and easy test to try next. :smile:

The waterpumps were originally metal, but it's wear over time that makes them less efficient rather than losing fins and being completely knackered.

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Swapped the coolant reservoir from my working 2012 fiesta and still no joy.

The coolant level in the tank would rise as the temperature went up and start to overflow until revving the engine hard, at which time the coolant level would quickly drop to normal.

From first start up, I pulled off one of the hoses feeding the cabin heater, and the coolant flow was quite substantial, which tells me the pump is pushing out coolant. 

Really don't know what to check next.

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There's still air in the system if the coolant drops when you rev it.  Air can be compressed, unlike water.

If we assume all parts to be working correctly, the only thing left is trapped air now.  It might be worth trying to vacuum fill the system to make sure there's no air in there.

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Update.

With the thermostat removed, everything seems to working as it should - it would get up to temperature, fan would kick in and temperature comes down. 

Just takes forever to warm up.

I gotta ask, what's the correct bleeding procedure for these vehicles anyway?

So far I've been bleeding it from the little nipple at the top of the radiator.

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5 hours ago, ifloochies said:

Update.

With the thermostat removed, everything seems to working as it should - it would get up to temperature, fan would kick in and temperature comes down. 

Just takes forever to warm up.

I gotta ask, what's the correct bleeding procedure for these vehicles anyway?

So far I've been bleeding it from the little nipple at the top of the radiator.

I just pull the bottom hose from the radiator, its a lot quicker lol

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11 hours ago, Martin-Fiesta-MK6-1.4 said:

I just pull the bottom hose from the radiator, its a lot quicker lol

.....and let all the coolant out?

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Does it get worse just after revving up? If so it could be the head gasket; that's what mine is doing. Get someone to rev up and down and feel if the top hose swells in time with it indicating the system getting pressurised from exhaust gasses.

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12 hours ago, ifloochies said:

.....and let all the coolant out?

ooops, i read it wrong, thought you meant the quickest way to drop the coolant lol

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On ‎7‎/‎26‎/‎2019 at 5:07 AM, ifloochies said:

Update.

With the thermostat removed, everything seems to working as it should - it would get up to temperature, fan would kick in and temperature comes down. 

Just takes forever to warm up.

I gotta ask, what's the correct bleeding procedure for these vehicles anyway?

So far I've been bleeding it from the little nipple at the top of the radiator.

They're vacuum filled at the dealers so no bleeding required.  They should self bleed through the expansion tank cap hole and the rad bleed point but some can be a pain. If you hear gurgling behind the dash that's the usual sign that they're not bled fully.

Have you been using cheap rubbish thermostats?  As with the rad cap, it's worth buying genuine, the aftermarket ones just aren't made to the same tolerances.   

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8 hours ago, TomsFocus said:

They're vacuum filled at the dealers so no bleeding required.  They should self bleed through the expansion tank cap hole and the rad bleed point but some can be a pain. If you hear gurgling behind the dash that's the usual sign that they're not bled fully.

Have you been using cheap rubbish thermostats?  As with the rad cap, it's worth buying genuine, the aftermarket ones just aren't made to the same tolerances.   

Strange thing is, from the very beginning, one day the car was running just right, and the very next it just started spilling out its coolant all over the place.

Talking about thermostats, when all this first started, I took out the original one and did the boiling water and thermometer test, and it was still functional - opening at 89 degrees Celsius. 

Subsequently bought two other replacement thermostats, one in a motorcraft box, and the other a FoMoCo item, but still had the problem when those were installed. 

Did a sniff test and it came up negative for combustion gases in the coolant.

Everything seems to be alright with it regardless of engine load, until it reaches 98 degrees Celsius + , then coolant rapidly starts to expand in the reservoir and temperature stays high at 105 degrees Celsius despite the fan kicking in and staying on, even after the engine has been shut down.

I have to say, this has to be the worst head-scratcher in all my years of car ownership. 

I have so far read some other owners report such issues on other forums online, some dragging on over multiple pages, but strangely enough not a single one reported back on how they had resolved it if they did indeed.

So what next, what can I check?

By design, are there supposed to be any restrictors in the bypass circuit that my have dislodged themselves, because really starting to run out of ideas on this one.

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11 hours ago, ifloochies said:

Everything seems to be alright with it regardless of engine load, until it reaches 98 degrees Celsius + , then coolant rapidly starts to expand in the reservoir and temperature stays high at 105 degrees Celsius despite the fan kicking in and staying on, even after the engine has been shut down.

Does the fan come on low speed at around 99c or is it only coming on high speed at around 105c?  May be an issue with the fan resistor if its only coming on high speed.  

It is definitely a head-scratcher as you say.  There aren't any internal restrictors to come loose.

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