I noticed a deep thumping noise while driving a few days ago. Took a look under my truck and there's a pinky size hole on the structural weld on the passenger side, right below the door.
How bad is it? What's the best course of action? What's the cheapest way forward?

Sent from my SM-G973U using Tapatalk

This might be an option.
All SafeTCap(R) Frame Repair Kits for 03-09 4-Runner - autorust.com

Maybe talk to some auto collision repair shops?

In the morning I was going to call up some more frame repair shops. I have none of the experience or know how to even start with welding and frame repair.
One shop said they would not be able to work with the frame due to the weird rusting that's going on. (That being almost all of the rust is located on welds and around body mounts)
Another shop had said the best option is to replace the frame entirely. Very expensive, and it'd have to be a frame from a cannibalized 4runner or separate parts welded together. Both still leave me with another toyota frame that will rust through.
Thank you though for the link. It may just save some cost down the road.


Sent from my SM-G973U using Tapatalk

Frame rust is a common problem with 4Runners unfortunately, especially if you live where roads are salted in winter. But another aggravating factor that you may be experiencing is that the AC drain in the engine compartment drains right on top of the passenger side frame rail, the condensate runs down the frame under the passenger side door, where it stops and starts dripping on the ground. But it starts rusting the frame where it stops. You need to run an extension hose from the drain hose Toyota has there and route it to the outside , away from the frame.
My frame had a 8" long x 2" wide hole in the bottom of the frame rail from this and i had a couple of steel plates welded in at the cost of $1000. Yours doesn't look too bad, even with the hole, but take a screw driver to the bottom of the frame in that area and see if it's still solid or you can poke through. If you can poke through may as well knock all the rusted part out of there and have it welded like I did.

Took my finger to the rusted bits, pushed into it like it was wet cardboard. Took 0 force to go through the frame.
Looks like I'll be doing this sooner rather than later.
Will be adjusting The ac hose later too. Thank you.

Sent from my SM-G973U using Tapatalk

Please keep us updated on the solution.

Mind showing a picture of the repair? I have similar rust in the area as OP, no rust hole and I took a hammer and tapped around the area, still solid..for now. Also, I recently re-routed the AC drain line.

Not a picture-poster, but if you go to my info page on here you will see it, I think. Just a couple of 3/16" plates welded to side and bottom of frame rail. If your frame is still solid in that area and you've relocated your AC drain line you've taken a good corrective step, now just put some type of rust preventative inside your frame through the various factory holes in it and you should be good.

Right now the hope is that she'll survive another six months.
I need to get new tires and coolant issues fixed desperately bad so that comes first.

Would wd-40 and a significant amount of bedliner stop the rust for a bit?

Sent from my SM-G973U using Tapatalk

WD-40 would only help very temporarily, bed liner will only trap what rust is there and it will continue to rust under the bed liner.

At this point to slow it down I would use a rust converter, inside and outside of the frame.

Been uncovering the issue over the past couple of weeks. Went in for a random service and got underneath. The mechanic pointed out some suspicious lesions. A hammer with a quick tap revealed multiple all the way through holes. I went under her today to take a deeper dive. Walked away with a grim realization - many more holes, everywhere. I'd check the front passenger A-arm where it curves up towards the outside wheel well. RDruss mentioned that area. He's been very helpful. I have two holes in that area and one along the weld. Check on my thread. It's atop the 4th gen board att,. These things rot from the inside out and I'm trying to decide what to do exactly. New frame is ideal. But no one seems interested. At least not in Northern VA. Good luck. Keep us updated.

What you want is fluid film or cosmoline. You can get both on ebay, and the fluid film also has a wand that you can buy for like $10 to go inside the frame and spray 360 degrees.

I like the fluid film for inside the frame and the cosmoline for outside.

Fluid film: lanolin based oily coating that creeps/self heals and is excellent at stopping rust. But it will eventually wash off if used outside the frame so needs recoating.
Cosmoline: military uses this spray wax to keep their equipment and guns from rusting. VERY effective and will never wash off but doesn't creep well. Perfect or outside the frame. These WILL both stop the rust in its tracks but obviously you can't undo the current damage without welding. I'd apply either or both very liberally until you can fix it.