16LT4

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GM somewhat quietly raised the warranty on injectors to 10 years/150k miles. I had one replaced earlier this year; I diagnosed a weeping HPFP via the GM test procedure, replaced it (scraping the intake valves clean while the intake was off), but still couldn't cure the -7% fuel trims and <1% fuel dilution. Knowing the recall, the dealer diagnosed a faulty injector. I had them replace the other 7 while they were in there, because if one failed, the rest aren't far behind, and I refuse to play "whack a mole." I arranged a little bit of price discount, and it only cost an extra $300 for them to do all 8 (with parts/labor warranty) vs. me doing it at my cost. As I'd already done two timing chains in the previous few months, I had them do the weeping front cover seal and oil cooler line at the same time.

Not to mention, illegal.

It’s a 5 year old used truck. What are you expecting?

The stock intake pulls in as cold a bundle of air as can be pulled; aftermarket systems pull warmer air with less filtration. Awesome.

From past used oil analyses, transfer case fluid is due for replacement by 30k miles. Change it.

Mine isn't capless, but I replaced that missing plastic retaining rivet within a week of purchasing my truck; after the first time fueling it up. No need to order GM parts and wait for them to arrive; your FLAPs carries them.

Watch your oil level. If it continues to read higher, you may have a HPFP issue. Check your fuel trims; if they are reading negative, that's further evidence of failed HPFP diaphragm. A DTC won't be stored until about -20%. I'll be replacing mine in the coming weeks; my trims were -5%. Two UOAs showed trace fuel amounts in the oil. When I disconnected the PCV line to the intake duct (making sure to seal all open lines to not create a vacuum leak), I saw my trims rise back to near perfect. That was enough confirmation to order a HPFP and hard line from HPFP to fuel rail distribution block, which is single-use. A CkPS isn't bathed in oil, but because it is reading a tone ring on the crankshaft, gets oil slung on it. New ones (at least on the other brand vehicles I've replaced them on) have o-rings to seal them and prevent oil leaks. Just something to watch in the future.

I'm interested in the slight mpg drop: do you notice this across a tank (on average), around town, on the highway, towing, etc? All else being equal, I'd expect to see a possible drop on the highway, but with a slight gain around town; the affect on the average being of course based on which driving environment the truck sees more. Can you quantify what "slight" is? As much as I would like 3.73s, I know I (most likely) won't be doing it due to my time (too many other projects) and that my truck is what we use predominately to run NY-OBX a few times a year, so I want to eek out whatever mileage I can. In a few years, we'll be looking at today through rose-colored glasses, remembering the "days of cheap fuel, when we didn't really care about mileage." I just like to see the numbers and data, especially on the gear ratio experiment. My '04 FX4 had 3.73s, but also tires that were upsized one sidewall size, and I could feel the difference accelerating from a stop. With only a 4 speed, the upsize was done not only for looks, but also to drop engine RPM on the highway a little, but I could feel it with a trailer.

My 4x4 '16, 5.3 with 6 speed, has G80 rear diff, factory trailer hitch and in-dash trailer brake controller. It also has with 3.42s, so I guess it didn't have the "official" tow package that would have netted 3.73s. Despite being an LT with factory center console and heated front seats, it also came with 17" wheels. I'm not up on the various option packages, but it seems to be some interesting combination of basic and mid-upper level features.

3.73s are what these trucks should have came with across the board anyway; the 5.3 likes/needs to rev, so the 3.73s would help motivating the truck, especially with any weight behind it. Mine has 3.42s. A few trucks ago I had a '14 Ram Laramie with the 5.7, 8 speed ZF, and 3.92s. Between the added power of the engine over the 5.3 (and better torque curve), the perfect shifting of the ZF and the towing gearing, the truck was easily much more comfortable with the same weight trailer behind it, and got the same if not better fuel mileage than my '16 K2 while doing it. Without a trailer, the Ram still achieved 22-23 mpg on the highway, despite more engine and more gears. A 3.73 in the K2 would have a negligible effect, if any, on fuel consumption, and may actually improve around-town mileage due to keeping the engine in its power band. I'd love to see data on that. On a lifted truck with larger tires, definitly need to "gear it;" the larger tires effectively "ungeared it," and probably puts the truck in the 2.xx realm.

Yes. I only post from personal experience. My 6L80 has a bottle of Lubegard and a tube of shudder fixx in it, and drives/shifts as smooth as can be with 107k miles on it. No rapid TC lock/unlock, no Chuggle, no lazy shifts, no shifting confusion. I drove it 190 miles one-way today and trans temps never got higher than 144*F. Fluid is either AC Delco or Valvoline Dex 6 (I forget what I have in it right now). My original 1986 2004-r is also living nicely behind the 350 in my car too, with a bottle of LG. I put in a bottle on every transmission I service, every time.

Lubegard, and in some cased their additional Shudder fix, works wonders on GM transmissions, or any older transmission. I run a bottle in every automatic transmission I own. Misfires are easy enough to see on live data on a scan tool; all engines can misfire to varying degrees without tripping a CEL or registering a DTC, some have a higher threshold than others. This is because ALL engines misfire. Without scantool and diagnostic data, everything will just be a guess.

I've ran my truck with the pill flipped, and now with the 70* updated thermostat. The only reason the pill is still not flipped is to increase the ATF heating rate during NY winters; with the pill flipped during January, I could drive 15 miles and not get ATF out of the 80*F range. On my '16, unfortunately, the ATF heat exchanger is liquid-air, not the liquid-liquid of the last several decades; I wish it was the latter, so it doubled as a heater.

190* is too hot; even 170* is at the farthest realm of proper. Here's my data points: After I upgraded the GM Thermostat two years ago, I towed my VW 200 miles on a car dolly (crossing NYC) in early August, and never saw trans temps higher than 162*F. This past December, I towed my 442 and my '84 GMC 200 miles each way on a 2k lb u-haul trailer on the same cross-NYC route, and never saw temperatures leave the 140s. This route, in addition to crossing NYC onto Long Island, also includes crossing the Taconic Mountains in upstate NY.

Car wash does absolutely nothing to prevent fender rot on these trucks. Nothing. Remove a tail light and shine a flashlight into the void, you'll see the upper surface of the fender well; THAT surface is what collects dirt sand sand, which retains salt and water, causing the rot. That area is impossible to reach with car wash, or even from inside the fender well; it is only accessible by shooting water around the fender well, either by reaching up with a hose, or by removing the tail light. I lived a decade in Livingston County, including daily driving my 442 through winters, so I'm no stranger to the salt out there. Rot occurs from the inside out, not vice-versa. Either way, too late now. Oh, my truck also gets driven literally through salt water when I take it on the beach. Factory rust-preventive coating on the frame rails is still there, too.

Miles or kilometers? I mean either way that's impressive, one just more impressive than the other. And please elaborate on "no major repairs," as "major" is subjective. Any failures, and if so at what mileage, of common things like HPFP, wheel bearings, injectors, water pump, etc? Steering rack? Vacuum pump? I interpret "major" to be cam/lifter related problems.

Or, just reaching an arm up with a garden hose to spray out the inside of the body panels. Every time I wash a vehicle, I start with the underside, nooks and crannies of the body seams, frame channels, etc. I'll even fill the boxed frames with water to rinse out salt and sand. One thing I learned as a teenager was to use a hose nozzle pointed back toward my face to clear the GM fender lips of debris, shooting water from the frame-outward. Just spraying out the inner fenders never removes the dirt/sand that traps moisture and sits above the fender lips. Forget about my '16 not having rust, but my '84 and '86 GMs that have lived outside their entire lives through upstate NY winters are also rust-free as well. It's a lot harder to repair rust than it is to prevent it.

Adding a drain plug is one of the first things I do on every transmission I have to service. I take a regular nut and castle it with a cut-off wheel. The slots allow fluid to drain; without them, any lip formed by the drain plug retainer will hold fluid, and more importantly, settled particulate (which never comes out with an extraction pump). Then I drilled a hole in the pan at a location that wouldn't interfere with either the magnet or the filter. Then I MIG welded the castle nut, slot-side down, above the hole. I used a new drain plug to center the nut and clamp it down for a brief tack. Drain bolts, with sealing washers, are readily available from any FLAPS, either 14 or 15mm hex head (I forget which). This is also the upgrade I highly recommend for anyone with a BMW; toss the 8mm allen drain bolt as far as you can throw it and replace with a GM drain bolt. Now, ATF changes are far simpler and easier than even dicking around with a fluid pump; remove drain bolt, let fluid drain while you walk away. Slightly pull dipstick to allow air. Come back, wipe pan, install bolt, fill trans, done. Easier and quicker than engine oil. The principal that I use for every machine I own is that maintenance prolongs their lives, and maintenance will occur more often when it is easy and convenient. Therefore, ease of maintenance prolongs a machine's life.

I monitored ECT with scan tool after making the change, and it stayed right at 195-197*F. The T-stat opened up as it is supposed to, and the fan was on. I went with the lower T-stat not because I care much about ECT, but rather its affects on plastic components, and the ability of heat to plasticize rubber seals. My BMW has ran at 220-230*F for the last 200k miles without issue, other than heat-hardened gaskets. Within 10 miles of driving, I did notice the on-board display of average fuel mileage increase by nearly 20%, and that's with nearly 100 miles on the current trip odometer. The truck has a smoother idle too, now that it isn't running fat. Fuel trims had indicated over-fueling, so after a few more miles I'll pull that data.

Does it matter? Replace the entire assembly, easy peasy. Mine was stuck open for who knows how long, and I just replaced it with Motorad 815194 from rock auto, the 194* T-stat in lieu of the stock 207* unit. $45, and easier to replace than a traditional thermostat (no RTV/gasket needed, the new houseing comes with an o-ring). Before replacing that, however, I 1) replaced the temperature sending unit to ensure anything I'd see on the scantool was accurate and 2) looked at ECT on a scan tool. The dash gauge is hardly an accurate gauge.

Yes that's it. 194* not 195*, my error. I edited my earlier post. No scouring needed; readily available on Rock Auto without intensive searching: https://www.rockauto.com/en/moreinfo.php?pk=8072292&cc=3315175&pt=10337&jsn=3854

Replaced the T-stat with 194* Motorad and took it for a test drive. Whereas before the truck spent most of its time in the mid 160*s over a nearly half hour drive, now it gets to 195* within 4 miles/under 10 minutes. The gauge needle also sits in the middle where it’s supposed to. I haven’t checked fuel trims, but they were negative before, so I’m going to wager they’ll trend upwards as well. What’s interesting is that I suspected bad T stat 2 years ago and had dealer look at it (under warranty) with negative fuel trims also, but they said it was fine. I never checked ECT at the time. Looks like I’ve had a bad T stat for a few years. I’m very curious to see if my fuel mileage improves now. At the same time, because more grounds are never enough, I added another main ground cable from the water pump to the chassis.

You might have to play around with how loose to make the lugs; you only need a few thousandths of an inch of play to break the rust seal. A wire wheel on a a $10 HF angle grinder makes light work of cleaning up the hub . I'm also in upstate NY, so most of what I touch has some various stage of rot or corrosion. A 6k lb Silverado is the biggest BFH you can swing at it. This is what you want on reassembly on most every fastener, the back face of the rotor, the rotor bore, the hub, etc. https://www.motorcraft.com/us/en_us/home/our-products/chemicals-and-lubricants/greases/high-temperature-nickel-anti-seize-lubricants.html

I'll be doing exactly this job in a few days, but went with a 194* opening temp 'stat instead of the stock 207* stat. My truck did NOT produce any DTCs nor driveability concerns, apart from being a little thirstier than before, and not completing the EVAP OBD2 test cycle (but no DTCs or dash lights for that). My gauge needle moves between the two marks to the left of center (1/4 and 3/8 if it were a fuel gauge), and monitoring with a scan tool showed a maximum ECT of 170*F over the course of a 25 minute drive at 41* ambient air temp.; most of the time, ECTs stated in the 162-167*F range.