Partway through the Oppo Rally, my wife's 2012 Ford Flex lost all of the boost from its EcoBoost engine. We withdrew from the event, nursed the Flex home, and won the "I Got Screwed" trophy. She made an appointment to have our local dealer take a look at it. While driving there, it lost more power going up a hill, belching thick clouds of gray smoke from the tailpipes. I turned around, coasted and idled home, and had it towed to the dealer instead. In the end, they replaced a valve cover gasket and both turbos, all covered under the extended warranty. Our receipt listed all related parts and labor at a price of "no charge," thanks to the warranty. But an article on Tundra Headquarters goes into detail about the cost of parts and labor to replace the 3.5-liter EcoBoost's turbos—around $2,250 in total. The article also says that Ford has claimed these turbos are designed to last at least 150,000 miles. Yet ours failed at just 58,000.
This would not have been an issue if the Flex was equipped with a 5.0-liter V8 (which is not an option). But both engines are available in the Ford F-150. According to the calculations by Tundra Headquarters, the point at which an F-150 with the 3.5 EcoBoost's fuel economy savings breaks even with the lower-priced but thirstier V8—assuming that gas at $4 per gallon—is 241,000 miles. This article was written in 2012, and prices have changed a bit. Current gas prices are much less than $4 per gallon, and the EcoBoost V6 costs $1,100 more than the V8 in the 2017 F-150, not $1,300 as written. As a result, we're probably talking closer to 350,000 miles to break even—a distance that the Flex could probably achieve, but likely won't.
So is the smaller turbo engine a better buy than the big one? In cars like the Taurus SHO, the Explorer, and the Flex, a V8 isn't an option, so the 3.5-liter EcoBoost is a way to get the power of a V8 regardless. But a V8 would probably fit in the Flex and Explorer if Ford wanted to make that happen. In the 2017 F-150, the V8 generates 385 horsepower, just 10 more than the 3.5 EcoBoost, and costs $1,100 less. At a savings of just three miles per gallon, plus the added complexity and repairs, it doesn't seem worth getting the twin-turbo V6 when you could've had a V8.