I will simply state the reason I believe your delta has stayed the same is potentially because you have gotten the crud out of your cooling system with that cooler, and there's nothing left to clog it further. Just a theory. Impossible to know without replacing it. Pulling a trailer uphill in 4th gear at 2700 rpm at 65 mph puts a truck under a much bigger load than your truck sees going down the highway. A healthy 6.0 cooler should keep your EOT within 10-12 degrees of your ECT while under these conditions. The P0012 code can trip as low as 16* depending on conditions, and trip at a maximum of 30* apart, so long as you've had that Ford updated tune. This means 16* there is something WRONG. low boost codes, low icp codes, etc all have a buffer where they will still be low, but not low enough to throw a code. One can take from this quite simply that at 10-12* apart cruising down the highway, is becoming an issue. Your options are to either let it go a little further (won't be hurting anything until a rupture) and risk actually having an issue, or replace now and not worry about it for another 100k miles+... My experience says your truck needs an oil cooler. 17* is a lot. If my truck (and many others for that matter) can run 65 mph even 75 mph with a 0-2 degree split, maybe 4* while getting off the freeway and the ECT falls faster than EOT, then you're saying that 500 rpm more allows for an additional 15*? I don't think you're wrong that your delta will be the same in a year, but I promise. Put a new oil cooler in your truck and your temps will come down. My old coworkers truck had small tires on it and 4:10s, his truck ran 2350 rpm at 65 mph. His truck ran a 5-7* split. If a 350 rpm gain creates only a 4-5* climb, you want to justify an additional 10* for 150 rpm?
If anything, your coolant temp being higher will only make your delta become worse. Reason being because your oil and coolant temps are separate, minus the cooler. So cooling hot oil with 179* coolant is going to work better than cooling it with 192* coolant. Understanding a heat exchanger does wonders here.
You say your 52 mph at 1900 rpm is not the same. It is not exactly, but not that different. So long as your truck is at thermostatic temp, 192, what on earth does air flow do for your oil temps? You get zilch for cooling your oil with airflow.
With an EGR delete, a 40 degree split hurts NOTHING because it is not the hot oil that hurts anything, it is the failure of the egr cooler that hurts it. I see 270* pulling a trailer uphill in my dmax. Doesn't bother me one bit, it is designed for it.
From earlier. 125* is certainly not ideal, however you will not damage the internals at that temperature. And if you change your oil when you're supposed to, it doesn't have enough time to collect too much moisture either. Nothing I can do about a healthy oil cooler. Today was warm outside. My Ford maxed at 188 ECT. Oil hit 187 while idling in a parking lot for 15 mins. Started driving, cooled off to 174. Literally nothing I can do about that. Nothing I need to do about it. Oil is changed every 2,000-2,500 miles in this truck.
What else was there? If you don't like my answers I'm sorry. For the most part, I do not need Ford's grace for my wrench turning. The dealership is not in business of fixing trucks, they're in the business of selling parts. I work on a lot of trucks that get towed in from the Ford dealership from the dealers either selling the wrong stuff, having no idea what they're doing, or other crap. I don't need TSBs in order to work/wrench on trucks. I have a 99%+ success rate at work and I don't get paid to misdiagnose people's trucks. If this means I'm doing things "WRONG" then I would seriously love to meet someone doing it right.
I mean this very sincerely. If you met me and watched me work on vehicles for a week, watched me diagnose trucks, watched how I do things, you wouldn't have anything bad to say about these things. I come off very strong because I'm very hard headed, and though I don't claim to be right, I simply state what I've learned from thousands of trucks and I will continue to help people based off of my opinions. If my opinions are wrong, feel free to jump in and give your opinion. But if your opinion is based off a few trucks here or there you've seen or worked on, or just from what other people have posted up on here, that to me is far less reliable than my years of experience working on these pickups. And please, don't ream me for having my opinions, right or wrong.
06 King Ranch
Fass 200, Custom fuel lines, 225/100s, Thumper stage 2 hpop, WPE stage 3 intake, Mishimoto radiator, Flex a lite fans, BPD water pump, MPD oil cooler relocate kit, Intercooler pipes, Compounds built by me, etc etc etc
05 Eddie Bauer
Resealed entire motor @ 170k miles, new lifters, 6.4 push rods, studs, rebuilt the turbo, IPR egr delete, new injectors, new heads, new ficm board, coolant filter, intercooler tubes, regulated return, bunch of other new parts. Factory exhaust, cat gutted(wife's rig). Livewire with gearhead tunes. Should go a while reliably for her!
03 LB7 duramax the "daily/tow pig"
Lbz cp3, s475/stock twin kit, built trans, steel driveshft, amsoil bypass, secondary oil cooler built by me, fass, traction bars, trans cooler upgrade, dual alts, straight center link + tie rod sleeves, efi live, transfer flow/tool box tank, 5er hitch, other small upgrades.. and most importantly, STOCK HEADBOLTS! Just rolled 200k miles, twins installed @ 165k, daily driven on a "550 tune" tows 18k on a "475" tune.