we had a 2009 ford explorer with 34,000 miles in the shop today with a ticking in the engine ford refused the warranty on the motor because the customer never ever changed the oil! this car had the original filter on it and the oil was like tar and black paint it smelled so bad that we had to put it in containers and take it to the collection center instead of dumping it into our collection tanks..The customer added oil when needed (he would have gas stations check it every so many fill ups) but never changed it. We pulled a valve cover and it was sludge city. We changed the oil and filter 5w20 mobil conventional with 1 quart of marvel and let it run for about 10 minutes oil was black already.but the tick was still there. I drove this car for about 30 miles or so and it seemed to quiet it down a little. We changed the oil again and used pu 5w20 and a new filter and told the customer to drive it for a couple of days and bring it back either way at no charge.. I should have pictures of the engine w/the valve cover off and i will take more after a few months (had to use my phone).. I agreed to do the oil changes for free so he will come back so maybe we will be able to see the cleaning progress. This was a really dirty engine but it was a tick and not a knock so maybe it can be saved. I should have kept some oil to send out but i did not. This is a beautiful explorer with all the options and the 4.6 the body shined and everything else was like new. Customer said there was no indication that it needed to be changed and said it is what it is!