I disagree based on my 35 years and almost a million miles of driving turbo 4cyl cars as daily drivers.
1. In city driving you seldom get into boost so the engine will get mileage equivalent to a NA engine of the same displacement. If you are someone that drivers idle to WOT constantly your mileage will tank but it will with a NA engine to and that is an issue with your driving style not the engine configuration.
2. Carbon build up and coking in turbos stopped being an issue 40 years ago when they started using turbos with water cooled bearing housings.
3. In city driving you are seldom in boost so the turbo is not generating any more heat than the exhaust of a NA engine under the same conditions. The cooling system of a turbo engine is sized for when you are making maximum boost. In city driving you have excess capacity compared to an equivalent NA engine.
4. Again in city driving you are seldom in boost so the load on the engine and heat being generated is no different than a NA engine. The oil doesn't have to work any harder than the oil in a NA engine under the same conditions. The oil may get the "crap beat out of it" but its from lots of WOT high boost time not city driving.
Hi dave...I should have clarified better....
With regards to MPG....in Los Angeles, etc. areas.....if you are in typically 5pm city gridlock type traffic.....it is now commonplace driving for people to expect that when an opening occurs or a move up occurs for drivers to literally gun their engines to avoid "cut-ins"....Santa Monica is very much famous for this...… if you don't, rear end collisions are very, very common....so many drivers still romp on the throttle.
Although carbon buildup has been greatly reduced, it is still an issue (no matter what the PR
material states)….. as an example, I use BG intake products and was purchase a couple to replenish my supply.....the regional distributor met me (surprising) because he was in the area...… he was having a very good day (older gent and car guy) and we got to talking about the new gen engines..... he advised they have unfortunately been good for his business.... he just did a follow-up with a fleet operation running both EB service trucks (F150's)...a total fleet of 300 vehicles..... their (BG) decarbonization systems which he sold them about a few months prior they were exceptionally happy with..... (included teardown inspections) reducing/cleaning the carbon buildup to a fraction of what is was.... they are hoping this will reduce or eliminate the annual $25K budget they have in their annual maintenance program for turbo replacement/rebuild/cleaning required or caused by carbon buildup/coking in the turbos and the 2-4 days of downtime per vehicle (typically about 20% of the fleet).
As far as heat generation, I don't think Ford has a TSB out on it, but most every mfg does have one regarding turbo cars/oil change intervals and specific advisory regarding gridlock traffic......my sister in law (who is an expert on everything) said pretty much the same thing that coking/carbon buildup has been gone for years..... she works in Beverly hills so traffic is a nightmare….. her BMW twin turbo V8..... although it is leased, they just replaced or rebuilt the turbos...… the gridlock traffic "cooked" the oil and caused bearing failures in both turbos...…
While I'm glad as many do who drive in typical conditions have had very good luck/experience, coking/carbon buildup (especially with turbos) still exists.