2012 Highlander limited keeps overheating.

How about the engine THERMOSTAT ?

Additionally, "had a guy look at it" doesn't sound like a professional diagnosis with the backing of any kind of guarantee by a trained technician at a licensed repair shop. We all make decisions in life to take risks - perhaps in an effort to save a few bucks. In the end, the consistent result is that many folks post here frustrated that they spent a bunch of money upon a guess or recommendation that didn't work, and are now seeking advice from someone in this forum on what to do (aka what to replace) next. The truth is, unless you have a proper diagnostic tool and a DVOM and a shop manual and a wiring diagram, you are often ill prepared to do anything on a vehicle newer than 1996. Add to OBD II in 1996 CAN networking in the 2000's and now it's absolutely impossible to perform proper diagnostic testing without proper equipment. Networking isn't about power and ground -- it's about data transmission. Seek guidance at a local repair facility from a trained technician near you. The alternative is to continue to guess, continue to be frustrated, and quite possibly create more damage to your vehicle by continuing to operate it with the overheating issue occurring. Last thought - yes, often times some of us know "pattern failures" that can be helpful to learn about, but take these with a grain of salt too -- just because someone has seen something before doesn't mean it's happening on your vehicle. https://repairpal.com/repair-shops/toyota-repair-and-service-in-memphis-tennessee