I bought a coworkers 2013 XLT 5.0 4x4 a few months ago when he upgraded to a 2018. I know the guy pretty well and I know what he used the truck for. He has a smaller bay boat (he has a 90 outboard on it if that's any indication of the size/weight) he took out a couple times a month. Highway almost exclusively other than that. I do not tow with the truck, although I have used it off road for hunting a few times.

As far as I know, he has had a new water pump and thermostat put in by the dealership (@60k miles I think), and with that a coolant change. He also had a break job done. Other than regular oil changes he has not done any other maintenance as far as I know. The truck had 96k when I bought it and is now at just over 106k.

I have been reading about doing transmission, transfer case, rear and front diff fluid change as well as spark plugs. I am 2-3x over what I see recommended on when to change these fluids. I think it would be beneficial to the longevity of the truck to change at least the t case and both diffs asap. Other people I've talked to in the past week are advising me to leave it alone unless I start having problems and are concerned about causing problems if I begin to disturb things.

Would it be best to change everything now? Should I do t case and diffs now and Trans at 150k? How critical are spark plugs at 106k? I plan on doing everything except transmission myself, and I may end up doing the trans myself depending on pricing.

 

Differentials and transfer are considered lifetime unless submerged in water. Although, probably: Lifetime = 150k

Plugs are due at 100k.

 

I swapped my spark plugs at 100k. Idle seems a bit calmer but that's the only benefit I can really notice. Spark plugs are cheap and easy to replace so I would go ahead and do it. I've made it a habit to change my tranny, diff, and t-case fluids every 50k. Truck shifts like brand new and I haven't had any noise from the diff.

 

Instead of talking to people to get opinions, read your manual and learn what should be changed. As stated, some fluids are lifetime. Plugs are 100,000 miles.

owner.ford.com for your manual if you don't have one.

 

I'm pretty sure the manual says plugs at 100,000 and diffs and t-case at 150,000. I think the only thing listed as lifetime is the transmission unless you do a lot of towing, then they do recommend changing the transmission fluid at some point.

 

Good to know that the water pump job has been done. The water pump is a known weak point on these trucks.

I would cease getting advice from the people that are telling you to leave it alone to avoid causing problems. Following that logic, we'd be best not to change our oil because the drain plug could start leaking. Ford and every other manufacturer creates recommended service intervals for a reason. You are on the right track with your line of thinking. Change the diff fluids and transfer case fluid. It's not that difficult for anyone that is even remotely mechanically minded and it's relatively inexpensive when doing it yourself. Use Ford fluids. There are some really detailed videos on Youtube if you need a guide. If you can't do them all at once, I'd prioritize your rear diff first because of the previous owner using the truck to put a boat in and out of the water. I would do the tranny as well. I let the dealer do a pan drop/filter replace/fluid refill on my trans and it ran me right around $160. I've seen a few members on here quote some insane prices for the same service. I'd check with your dealer and decide whether you want to do it yourself or let them do it. Either way, I would see that it gets done. I can't really offer any insight as to how critical it is to change the plugs right at 100K but I will say that it must be a relatively easy job on the 5.0 and the plugs must be reasonably priced because my dealer changed mine for $206 parts and labor.

Take care of your truck and it will typically take care of you.

 

My truck just rolled 50k. I will be servicing the trans and rear diff.

 

Those are some of the videos I was talking about. And just to clarifiy, my comment about recommended service intervals was in reference to people advising that you not service your vehicle. I'm not saying that you should wait until 150K miles to perform a particular service just because that's what the manual calls for.

 

I realize that you're talking mostly about lubricating fluids, but I think radiator flush at 100K is also recommended. Although that may have been done at 60K with the water pump work. I just bought my vehicle with 105K miles, so I'm looking at doing all of this soon too.

Edit: Never mind. I just re-read your original post. Coolant should be good for a while.

 

My 2012 had water in the front differential at 85K. Never submerged. Had both differentials fluid changed. Rear was very dirty.
Don't know how water got in. Maybe condensation? Check yours would be my advice.
Also needed new speak plugs at 55K... Ecoboost was running rough a nd missing under acceleration.
John