Cleaned EGR valve, not sure if full circuit is needed. 111k miles

Excellent pictures of the cooler. Again, worth noting this is at 111k miles. Can’t imagine any “cooling” took place with that. And only pinholes of flow left. It’s patently obvious Toyota rushed that nonsense to market without testing.

 

Escalate to lye (sodium hydroxide) solution? Hopefully available in the States, say on Amazon. We got some a few years back for soap making, on Amazon.ca. I noticed it's oddly missing from grocery/hardware store shelves. Apparently used in meth production.

If you're not doing this: most expedient is to cork one end of the cooler, then only about a cup of solution is needed. A bare wire run through the fins may expedite the solution's ability to penetrate.

Whatever solution is being used, I've found a one hour soak, then rinse and repeat, to be most effective, just judging from the amount of foaming reaction. It tends to be quite active at first, then subside.

Stumbled on this US lye source:

Online Store

 

You wasted 12 hours.
Oven cleaner. 30 minutes.. Pressure washer.
Repeat if needed....