Hi, I’m new to the F150 forum. In June I bought a 2016 F150 XLT 3.5 EcoBoost with 101,000 miles. When I bought it there was an O2 code on a sensor upstream of one of the Catalytic Converters. The dealer gave it a tune-up and replaced all the O2 sensors and it didn’t clear the error. They replaced both Cats with OEM parts and it cleared.

Fast forward to last week: I noticed the truck was running hot and found that it was very low on coolant (heater not hot should have been a clue). The truck took 2 gallons of coolant, but there are no signs of a leak and no coolant in the oil. It appears to be a slow leak (guessing ~4 gallons a year) and the truck runs fine. I’ve read that the coolant can leak into the turbos, but I don’t have experience with turbos.

Is it possible that the coolant is passing through to the exhaust and caused the original Cat issues?

What are the most likely hidden coolant leaks found on this engine? Thanks in advance for any knowledge shared.