Someone from our outfit recently got rid of '15 Explorer with only 44,000 miles on it. The passenger compartment really got dusty on (of course) dusty roads, and on trips sometimes they would actually "not feel good". It turns out there are many police departments and individuals having carbon monoxide issues with their explorers. Learned today Ford is doing a limited recall. You'd be doing a favor to pass this along to anyone you know who may be affected. I've heard that some have needed new exhaust manifolds, but the recall has no mention of that.
http://www.reuters.com/article/us-ford-motor-emissions/ford-offers-repairs-to-prevent-exhaust-leaks-in-1-4-million-explorers-idUSKBN1CI2N3
http://www.reuters.com/article/us-ford-motor-emissions/ford-offers-repairs-to-prevent-exhaust-leaks-in-1-4-million-explorers-idUSKBN1CI2N3