Well my 2011 Prius started rumbling 2 weeks ago. Pulled the plugs and shoved a usb phone endoscope down and saw coolant in #1 cylinder. Called for a repair and was flabbergasted at the quote of roughly $3,100. Other places were similar in price. I don't know any independent mechanics so dealer was the least hassle and quickest. 1 week later and one expensive repair, the car drives on. After getting it home, I again pulled the plugs and used a camera to see if anything changed as far as cleanliness. I expected something for that amount of money since they had the heads off, but nothing was cleaned. I also pulled the EGR valve and cooler off for the first time and was extremely happy to see light through the cooler. After 2 cans of brake cleaner, even more light could be seen. I was a little amazed at seeing light before the first cleaning after reading stories on this site. I was more curious if the EGR system was clogged to the point of possibly causing the head gasket issue. Based on me blowing through the EGR cooler before cleaning, I'd say I lucked out. Every time I have to go to a dealer for something that I can't do, reminds me why I do as much as I can myself. At the going service rate of $150/hr, I probably save $5k or more in labor.
Try soaks with (powder format) "Oxi-Clean Versatile Stain Remover", dissolved as concentrated a solution you can muster, in hot tap water. Cork one end of the cooler and pour the solution in, prop up (corner of laundry sink works good) and wait about an hour. Rinse and repeat; four or five sessions and it'll be like new. May need a little help from a wire, to both loosen and get the solution into all the corners. Don't use this solution on the rest of the egr system though; it's overkill, and may be detrimental to aluminum and ferrous metals. The cooler is stainless steel though, impervious. Don't neglect the intake manifold either: it has narrow EGR passages at each port, and surprise, surprise, the first to clog is cylinder one, then two, and so on.
