The infamous B-Max boot leak

The B-max is prone to water entry into the boot. Mine had been absolutely fine until I had a bumper repair and then water appeared in the spare wheel well and saturated the boot underfloor carpet/soundproofing. It seems likely the bumper repair has affected something but the bumper itself is now potentially fragile and I doubt if I can remove it to check anything without damaging the paint. I did however strip out the boot contents, floor, and side trims to investigate. Reports online suggest that some holes in the bodywork- usually covered in waterproof tape, can permit water entry. Checking my boot I found the tapes on the left side to be intact and dry- those on the right were detaching. They oozed moisture and leaked water into the boot when it rained. I removed the leaking tapes.

This revealed 3 holes, the middle one of which opened to show a foam sponge which was itself wet. Water was entering the boot from the rounded hole towards the bottom.

I sealed these holes with Tiger bond before smearing more of this over the metal and around the holes. I could then cut a piece of form-card to shape, and heat it with a hot air gun so that it became flexible. As it did so I pressed it back into the tiger bond so that it conformed to the boot wall and stuck there. Finally, I added more bond around the patch and sealed the upper round hole with a grommet.

This has stopped the water entry to the boot BUT its not a fix because Ford clearly did not expect any more than small amounts of water in this spot. If they had, then they would surely have found a better way to seal the body than just tape! Consequently there must be a leak elsewhere that is admitting larger amounts of water.

The reports I've seen suggest two sources... There is one- probably least likely, that can derive from a detachable plastic panel beside and behind the  rear window.  This is shown in green below.

It appears that this is held by clips and in theory can be removed to check for leak points. I don't think this will have been disturbed in the bumper repair so I don't think its the likely culprit in my case. Anyway,  I'm not removing this as it will undoubtedly break clips, spoil the paint and never go back properly. However here's a couple of pics from the fb group courtesy of Terry Brown to show this. The likely leakage point is circled in the close up on the right.

The most common source appears to be from the 2 air vents (1 each side) at the rear of the car and hidden behind the bumper. Since my bumper had been removed for the repair, its possible these were damaged or misplaced on reassembly. The vented  plugs are appx 15cm square and the right side one is shown below as number 28OB-62.

The panel is shown here with the bumper removed- not my car, I didn't want to do that so its a stock photo to show what the things look like.

This is a new panel seen from behind. 

Looking closely at the panel from behind you can see that there is a lighter coloured ring of sealing material around the edge that should seal the panel to the body when the panel is fixed tightly. This means that the vent panel needs to clip tightly into place for this to work and for this reason it has these plastic latches.

Latches that should griup the car body. These can be damaged if the panel is removed- or possibly simply loose their tightness as the age.

Obviously, I didn't want to remove my bumper, so what follows will probably come under the general heading of a bodge, but by removing the rear light, it was just possible to reach the vent top edges from above with my fingertips and the bottom and sides from below by reaching up behind the bumper. Take car in doing this though because there is very little room and it will scratch. It might help to remove the road wheel. Its best to pull the bumper forward a little as you reach up. I could tell that the vent panel was loose, but I was unable to clip it in any more tightly. Using a gloved hand I  squeezed tiger bond onto my fingers and  then smeared it into the gap between the car body and the panel all around the vents. It took several goes before I was confident I'd pushed the seal well in, all the way round the vents. Its very awkward but it can be done without removing the bumper. There was however no way of photographing my attempts!

Well, the first attempt didn't work entirely. I taped kitchen roll around the boot to locate the sites of water entry. 

rolled up tissue beneath the rear seat.

and along the sides

..along the hatch line at the rear of the boot

... and of course in both the corners... this revealed water ingress in both corners. 

Tissue has become wet in the corners- despite the form-card seal.

Tissue wet in the corner even though this tape did not appear to be loose or leaking.

Leakage was seen in both corners, but worse in  the as-yet unsealed lhs.

I added additional coats of tigerseal to the rhs and also sealed the lhs with form-card exactly as I had the rhs. This was effective and the boot remained dry for a week. However after that time I did notice a few spots of water in the lhs corner. At first I'd assumed that this was leakage past the form-card seal, but closer examination showed that in fact this was dripping from  higher up and appears to be leakage through the rear light cluster.

Removing  the rear light shows that it has 2 seals; there is a rubber seal attached to the light cluster itself which will seal against the car body and looks very much  like a water seal.

Rear light seal- note the attachment bolt and wire connectors in place. Note the  the black primary water seal that surrounds the connectors and which will press tightly up against the car body when the cluster is fitted..

There is also  a foam plastic seal which surrounds the wire emerging from the car body and which is actually stuck to the car. This isn't a  primary water seal. Examination shows that this foam seal is disturbed whenever the light is removed and the wire pulled. If the glue starts to fail then this square of foam can move and become distorted. It can get jammed between the primary seal and the car body. You can tell if this has happened because the entire foam seal should be evenly "foamy". If any parts have been squashed flat then these have been caught behind the primary seal, preventing it from doing its job. Water can then enter the light fitting and drain out along the flex connection. This water will then drip from the flex directly into the corners of the boot and end up in the same place as leakage past the form-card. 

To correct this I cut some new foam and stuck it around the hole through which the flex emerges. I cut it in such a way that this foam did not obstruct the primary seal. Finally, I refitted the light and waited again to see what happened. So far all has been dry despite some very heavy rain.