Hello hello.

Hoping anyone has any information on this, or at least I can add to what may be a common issue with the MK8.

Context: I recently acquired a 2020 ST-line 125 edition and I'm really enjoying it, has everything I want and need. However, after a week of constant rain and a trip to West Scotland I noticed the car losing it's nice new (to me) car smell and becoming a little musty. 

 

Upon inspection I found some light mould on the boot liner. I noticed this viewing the vehicle but figured it was the valet bay pressure washing the boot liner and it not being dried properly. Annoying but not a huge issue. After having it out and cleaning it I looked a little deeper and noticed some water in the wheel well. All three bungs had been punctured, so I thought maybe they were letting in spray. Ordered replacements. However, after checking again in the morning after a rainy night, I found more water. So it can't have been spray. I then went into a deep dive and found the right hand trim piece and sound deadening to be saturated and full of mould. I've dried and cleaned what I can and will replace the sound deadening. 

What I'm asking is what's the likely cause? I'm thinking it's the pressure flap behind the bumper not closing properly. Everything else looks okay, boot seals, rear lights, grommets etc. I need to stop water from returning as I really don't want mould in the car. 

Before anyone says take it back to dealer, there's not much trust there. I'm a practical person and a previous mechanic. The cost of sorting it myself is much easier for me when compared to the hassle of getting someone else to. Want something done right, etc.

Any input on where to look next greatly appreciated.

6 hours ago, Evey808 said:

Hello hello.

Hoping anyone has any information on this, or at least I can add to what may be a common issue with the MK8.

Context: I recently acquired a 2020 ST-line 125 edition and I'm really enjoying it, has everything I want and need. However, after a week of constant rain and a trip to West Scotland I noticed the car losing it's nice new (to me) car smell and becoming a little musty. 

 

Upon inspection I found some light mould on the boot liner. I noticed this viewing the vehicle but figured it was the valet bay pressure washing the boot liner and it not being dried properly. Annoying but not a huge issue. After having it out and cleaning it I looked a little deeper and noticed some water in the wheel well. All three bungs had been punctured, so I thought maybe they were letting in spray. Ordered replacements. However, after checking again in the morning after a rainy night, I found more water. So it can't have been spray. I then went into a deep dive and found the right hand trim piece and sound deadening to be saturated and full of mould. I've dried and cleaned what I can and will replace the sound deadening. 

What I'm asking is what's the likely cause? I'm thinking it's the pressure flap behind the bumper not closing properly. Everything else looks okay, boot seals, rear lights, grommets etc. I need to stop water from returning as I really don't want mould in the car. 

Before anyone says take it back to dealer, there's not much trust there. I'm a practical person and a previous mechanic. The cost of sorting it myself is much easier for me when compared to the hassle of getting someone else to. Want something done right, etc.

Any input on where to look next greatly appreciated.

I had the very same issue and lots on YouTube and elsewhere for it too.  I did the following, removed rear lights and tiger sealed every  possible mating face including location grommets, where the roof weld seem meets around the boot hinge area sealed, removed the roof gutter rubbers and sealed all underneath paying special attention to the rear most weld seam.  In my case, for now, seemed to work, no bumper removal  has been required just yet 

The tail lights are hiding the source of leaks into the spare tire compartment I think the buildup of organic debris from leaves bugs and road dirt leads to water not being able to drain out and it makes it into the cabin from underneath the rear lamps. I just recently found that the spare wheel in my 2016 Fiesta ST had been sitting in about 25 mm deep puddle. My investigation resulted in removing the rear lamps and cleaning the parts and surfaces where they mated and then adding a heavy duty duct tape to the exposed holes to prevent what could be described as overflowing water from entering the cabin. I am going to do the same on my 2011 mk 7 Fiesta and will take a few pictures to post up showing the areas of concern. 
This is one of those little things that can become a big problem if ignored!

Update: I think I've found it. 

 

At the top of the boot there are seams on either side and on the right hand side (where the leak was) there were some gaps in the sealant. 

I've resealed it with Sikaflex and it seems to be holding.

The sound deadening was beyond saving and I've had to throw it away as it was laden with mould. I'm yet to replace this but it isn't any noticeable in road noise. The trim and boot carpet were able to be cleaned and disinfected. 

I've also refreshed the interior with an Aircon cleaner to help remove any traces of damp smell.

So, a simple fix. Which is great news for me. I am shocked that several professionals had a go and failed, leading to the previous owner selling the car. More so disappointed with the dealership for not sorting it correctly before flogging it. 

Hoping this is a one off but something to check if you're finding yourself with an aquarium in your spare wheel well!

It’s a problem with literally every version of the Fiesta whatever part of the world it was assembled in.

Next week I will put together a pictorial post about the most likely places where water can find its way into the cabin. The most common places being in the rear of the Fiesta.