Small hole in lining of rear wheel well (not bolt)

From what Im seeing, I think the picture is showing the plastic liner in front and slightly above the mud flap (all the way in the back of the wheel well). It’s not the “tar” we see that’s sprayed on sheet metal surfaces of the well.

 

I covered mines already with 3M undercoating sealant. I have no moon/sun roof anyways. I think the holes appeared later just like the bolt holes appearing after driving few miles.

 

Your 4runner body is now going to instantly rust from the inside out.

Seriously though, I hope this area isn't one that ever ends up seeing any water flow through it! If it’s a gusset, as I suspect it might be, have you looked to see if there is a similar opening further up hill?

At the very least, I would poke a hole in what you sealed up in a few months (after it experiences rain) to double check you haven't collected any water in there.

Also, how are holes appearing?

 

My ‘21 had this, took it to dealer. Conveyed rust concern- especially the pocket slit being a trap for all the salt that bless our roads in Indiana in winter

It was repaired under warranty.
DIY works too with rubberized undercoating spray can..

 

Wow that is totally different advice than I got.

 

The reason for the variance in advise is that pretty much 100% of service advisors will make shit up if it’s the most expedient thing for them to do. At least for warranty claims.

I probably shouldn’t generalize, but I’ve never had an interaction with any dealer brand, for a warranty claim, where I was not lied to in the most obvious manners. Often times the interactions start out pleasant enough, they seem very professional, and I “want to believe”, badly!!!

However, never have I left not feeling like was brushed off or lied to, with a smile. This is over the 8 new cars over the course of my life. My last interaction had the advisor become “busy” and kinda lose interest, and started taking other people’s questions as I tried to show him that the mechanic did not resolve a squeaky rear seat-back by just moving stuff in my cargo area around. They also opened my door into a concrete wall at some point, so I got a nice paint nick to look at as a memento for that visit.

Mac1usa’s advisor was close, and at least didnt do something to “fix” a purposeful step in the production of the car. He was probably wrong about what it was, but he didn’t close up a hole that was put there at the factory, in a very consistent way, on all 4runners.

Oh boy, I got started…. Gotta take my meds now lol.

 

So I was under my 4runner, like I always do, cleaning out mud, like I always do…. And I got an underside perspective on this opening. A change in perspective can sometimes reveal and clarify lol. Yeah, I had other things on my to-do list this evening, but you know how that goes.

I tried to get a good light angle to reveal some contours. Several similar pictures with different angles of light help reveal what I believe is the real purpose of this whole arrangement :













My conclusion on the most reasonable explanation:

It’s not a gusset per se, but rather it’s likely a doubler panel that is used to manage seat belt forces experienced by an occupant in a crash.

The doubler panel likely reinforce the seat belt bolt mount itself, protecting from the possibility of the bolt tearing through in a crash, AND the doubler panel would then share crash force load with the adjacent panel via the fact that it appears to be a gusset/bridge to the next panel over. I bet the two deep divots (outboard of the bridge) actually pass through the wheel-well steel into the inside where it’s welded to another area that is doubled from the inside. (If anyone ever takes the plastic off in the interior, post a pic to see!)

Basically, what appears to be “a random hole”, or a “defect”, is likely the lower part of a purposefully placed panel designed to bridge the forces the belt bolt experiences in a crash, over two different panels (the seam of of the two panels is seen inside the hole).

Additionally, the geometry of this bridge (45 degrees draped over a 90 degree angle), combined with the forces that would be pulling the bolt forward in a crash, appears to suggest it is to promote bending/crumpling in a controlled manner instead of a bolt simply tearing through one layer of sheet steel (or, if it doesn't tear…pulling the sheet steel too far forward in a crash). Either scenario would result in a loose occupant, or a completely unrestrained occupant.

So why the hole??? I believe it’s to prevent moisture inside the cavity made by the bridge. The gusset/doubler does not seem to be open on the top, so my conclusion is that it’s left open on the bottom to keep condensation from collecting inside this hollow cavity. Corrosion in this area would happen quickly with contained water sloshing around in there, and would compromise the seat bolt’s strength in a crash, or the progressive/controlled deformation of this area when the seat belt bolt does it’s ultimate duty.

I would recommend this opening NEVER be sealed up!!! If you are worried about corrosion, spray some fluid film in there and call it a day.

 

It's a drain, don't touch it

 

You know what is very weird to me though if this is a drain why don’t we see some sort of tube around the edge of the hole?

The water has to travel in a tube right?

 

It’s not a drain for something else. It’s a drain for itself, so it can air out when natural condensation happens in the cavity. For example, when the car is very cold, and then enters a warm garage… or other sharp temp changes that will cause condensation.