My owners manual states that 4A can be used in all conditions, I don't have 4A, but if I did, I wouldn't be afraid to run it.

 

My truck's drive modes are completely separate and independent from the 4WD mode selector. My manual does not recommend or discuss using certain drive modes with certain 4WD modes. It says 4A is "appropriate for all on-road driving conditions including dry road surfaces" and 2H "provides optimal smoothness and fuel economy at highway speeds." No other warnings or recommendations. I think if Ford had a preference it would say so.

In the absence of any real-life data or experience, I don't think excessive wear should be a concern. The front end drivetrain is no less robust than the rear end, which receives 100% of drivetrain torque 100% of the time in 2WD/2H mode and is expected to last the life of the vehicle, The expectation for the front end, which in 4A receives less torque than the rear end (or none) under most conditions short of ice or mud, should not be any less. In my past experience, full-time 4A in another vehicle made no difference in wear or service life.

I may investigate the fuel economy and "smoothness" of 4A as the default over a road trip or two and check back with any findings.

Thanks for the ideas!

 

We’ve had 80 inches of snow here this winter and I have rarely used 4H on the roads here in Minnesota! Only time I ever need it is on the crappy gravel road to the barn! ( I normally have a couple hundred #’s of horse feed in the back as well! I’ve never had 4A so I guess I can’t miss it! Besides my UPS truck is rear wheel drive with dually’s! Most of the vehicles I see in the ditch are 4 wheel or AWD! Makes most people overconfident!

 

Whenever my IWEs are making noise (usually in the cold when they suck at holding vacuum) I'll use 4A to ensure I'm not getting any grind or one of the IWEs engaging when the other isn't. Consider the Expedition has a very similar driveline and defaults to 4A full time.

 

I agree with you on the concern about wear. And to add to post I use 4A quite a bit and notice a small hit to the drivability part like accelerating and turning and a small less than 1mpg hit usually. I would assume just having it in 4A on dry roads wouldn’t even affect the MPG much when it isn’t kicking in to 4wd. I’m usually using 4A when driving over our mountain pass and it’s a “chains required on all vehicles except 4wd/awd”. The last time I drove over the pass in those conditions (350 miles) I was in 4A 98% of the time and got 19.4mpg which is less then 1mpg lower then my normal highway MPG.

 

Good info, thanks!

 

I concur that any fuel economy penalty should be on the order of 1 mpg, but bear in mind that this is a 5% hit if you are getting 20 mpg normally. That equates to almost $1,000 over 100,000 miles.

My last driveline repair was a front driveshaft on my E-350; the hubs are manual so it is effectively in 4A (the "A" in this case is my arm moving the transfer case lever) with the front driveshaft spinning from late October to mid April. The bill for an over-the-counter rebuild at 150,000 miles was $500. The parts price on an F-150 front driveshaft is about the same cost. My personal thought is that bearings and joints that are not moving will likely go a lot longer without the need for a rebuild than parts that are in motion. I'm not afraid to use 4A, but I fully understand that doing so will cost me in fuel and repairs.

 

Just spoke to my neighbor who has a Hummer 3 which is basically just a Tahoe. It is AWD. His front diff just grenaded and took out both driveshafts along with the diff.

 

Agreed with some of the more recent comments here. It boils down to wear and tear. Using 4A all the time will cause more wear on the front end drive components, drive shaft, and clutch system in the transfer case. Using 2wd will minimize the wear on those components and maximize fuel economy.

While I don't have 4A on my XLT, I would definitely use it in the winter if I had it. As it stands now, I probably only put my truck in 4H a handful of times or less each winter.

 

There's no doubt it will cause more wear and tear. The question is whether or not that wear and tear is going to be enough to matter over the span of ownership.

Regardless, I don't see any reason to leave it engaged year round. I sure wish I had it though. I will not buy another truck without it, which means I probably won't buy another Ford.