1.0 Liter Overheating

[One liter wonder]

At the end of this story I replace my coolant expansion tank and cap - and also the burp line. And for a new burp line I used rubber tubing from Napa and not the $70 part.

My 1 liter fiesta with about 130,000 mi on it almost overheated a couple years ago. It got pretty low on coolant but never empty. Turned out to be the connection between the turbocharger return line and the connector where it goes into the expansion tank. I replaced the hose with the original equipment part at a cost of around $50. I discovered this problem when I noticed that the fan ran a little bit too long. One morning after I got to work. I checked the coolant. It was low. Not empty.
11 months later it failed again. The part was replaced under warranty at Ford. And then 6 months later I got into the car one morning and it ran rough for about 3 seconds. So I'm thinking head gasket leak and I look at the coolant tank and it's low. But once again not empty. For the life of me, I cannot see anywhere that coolant is coming out of the cooling system. There is not coolant in the oil. I add some more coolant over the course of a few days. One day I get home and it won't start. Crank all you want but it won't start. Some kind of system interlock that the car has built into its computer. You only get so many chances.
It took me a long time to find out that the expansion tank was bad. And to actually see the place where it was bad. I had to take a saw and cut a triangle out of the side of the tank. When the tank gets over pressurized for any reason, the blow-by goes out a secret passage to the bottom of the expansion tank - out a little tiny mouth that is underneath the 21 PSI radiator cap. After the fluid leaves the expansion tank it falls onto what I'm going to go ahead and call the frame and rolls towards the back of the car and you never see it. And if you see a puddle on the street you assume it's from the air conditioning cuz that's where it lands. But mostly it doesn't land because there isn't that much of it. It's a tiny bit over a large number of cycles.
I used a $28 aftermarket expansion tank that fit perfectly. I broke that burp line getting the tank off and no surprise that ridiculous nylon tubing that they used. And once it was shattered it was just completely useless.
I was going to use Tygon tubing and there may be a correct Tygon tubing to use in this situation but my host at the Napa store insisted the temperature range of the Tygon was too low and I should use this rubber tubing that he came up with instead. And he sold me a couple tiny little pinch clamps that let me use the original connectors that plug into the expansion tank and the side of the engine.
I had to take a close-up photograph of the hidden leak on the inside outside of the tank. As a whole, the plastic is still intact, but there are hundreds of little fractures. See the photographs.
And back to that head leak into the cylinder. You've seen these head gaskets before if you've taken the engines apart and sometimes even if the gasket isn't blowing, you can see where coolant was making it from the cooling passageway almost into the cylinder, but not quite. What I'm saying is I think there is a tiny possibility sometimes that you can plug that leak without going all the way to the head gasket. Because it's not really a leak. It's more of a weep.
Got the suggestion from a service manager to use K-Seal.
Got a couple thousand miles on it now. Seems fine.
Hope this helps somebody.

 

[Handy Andy]

If this stays together - these ideas are a great way to help anyone whom gets stranded on the side of the road, back up and running again!

Thanks for sharing this!

 

[scotman]

The integrity of the coolant reservoir has been poor since the beginning. Just because the plastic might be good enough to get the car out of the warranty period does not make it a good design. The thermal shock of heating and cooling seems to embrittle the plastic to the point of failure. The potential for even a tiny head gasket leak introduces the problem of crankcase or cylinder pressure being introduced into the cooling system. Neither of them being desirable. This condition is going to cause the cooling system fluid to boil at a lower temperature than normal.
I have experienced sudden catastrophic failure of the coolant reservoir on my ST. And a fortunate discovery of a failed reservoir on my 2011 SE. Thank God for the wide availability of the Dorman aftermarket replacement parts!
I can only recommend that anyone who doesn’t know what the age/condition of the reservoir in their Fiesta is should just replace the damn thing and reduce the chance of blowing up the engine.

 

[One liter wonder]

Micro cracking of the reservoir causes cyclical, pressurization and depressurization of the coolant contents of the engine.

Original poster here. The place that I found the cracks in the expansion tank, which I called the "inside outside", can only be seen if you cut the side of the tank out as I show in the photographs above. The place the tank was actually leaking is above the general high tank level. This means that when it does leak there, it mostly leaks vapor only, and no actual liquid. The actual vapor that leaks through the spot in the photograph goes directly into what can only be called the overflow tube. This overflow tube is where the little Port under the pressure cap is designed to vent to. It is a safety issue to have it go out the bottom and not into someone's face. So that part of the design is solid. It was probably the manufacturer of the dual pressure tank wall at this overflow tube that has been the Nemesis of this engine.
In particular, when the engine is shut off. There is no additional cooling going through the radiator. This is likely when the pressure is highest - as the engine cools down under the hot hood. I look under the hood after I drive once in awhile, probably not as often as I should, but I could actually look under the hood occasionally after a long drive on a hot day and see the turbo return line boiling into the pressure tank. When the tank came up to full pressure. The boiling would stop. Mostly. I say mostly because that is when these micro cracks in the coolant tank were the largest and allowing the greatest volume of vapor to escape. All of this right on a knife edge of engineering. The tank could have been larger or made of metal or just made of thicker plastic and everything might have been fine.
I am glad to see that there are people that come to this forum. I really hope some person benefits. From what I've written here. The car is still running fine. It's been a few thousand miles now.

 

[One liter wonder]

One more thing. That K-seal that I used... That stuff has a really strong safety statement on it. And I could surely smell it when it was in my shop and tell that it was probably not good to be around very much of the vapor from that once it's mixed with hot antifreeze.
I hear that K- seal works on the Ford Ranger too. And apparently there is some kind of similar product that comes in a smaller container as an actual Subaru part. Have you ever heard the story about Subaru motors needing new head gaskets....? This stuff was meant to prevent that from happening. And I guess they sell it at the parts counter at the dealership.
Just sayin'.
D

 

[scotman]

Regardless of the engine displacement or cylinder count, the coolant reservoir is a root cause issue for many overheated engines.
these reservoirs can have very “sneaky “ leaks that can easily be missed by owners who don’t make hash marks on the reservoir with a sharpie felt tip pen and then regularly look at the coolant level.
The reservoir in my 2016 ST began to slowly lose coolant over the past two weeks. I ordered a replacement when I had to give it a second topping of coolant!
The cost of the replacement part is cheap compared to the cost and inconvenience of a burst reservoir on the road.

 

[One liter wonder]

I'm glad you got a new tank before something horrible happened. I am the original poster in this thread and I want you to know that my 1 l fiesta is still going down the road.