Gandalf

That’s good to hear about the effect of blocking the two CAI ports. I did it with some cheap rubber caps. The air will also be cooler, especially if the CAI is a completely closed box with only the one fender inlet open. Like most of us owners of the first generation of the LT engines (2014-2018), and possibly the second generation as well (2019-), I’m impressed with the horsepower and efficiency, but really don’t like the almost built-in age limit of the engines, due to the GDI system. I can’t see getting much more than 200,000 on the trucks without pretty major carbon cleanup. Thanks for sharing your experience.

Thanks, pokismoki. I do have one breather on the front of the passenger side valve cover, and I’ve eliminated both vents on the CAI tube. The driver side vent is capped, as I installed an oil cap one-way vent breather on that side. (https://www.c-f-m.com/performanceparts/pc/CFM-Performance-Billet-Valve-Cover-Breather-for-2014-15-Chevrolet-SS-Sedan-L3-6-2-p1803.htm). My main concern is the gases escaping via the breather on the passenger side, and occasionally from the oil cap filter, which inevitably enter into the cab a bit. I’m probably worrying over nothing, as the crankcase with my setup cannot ever become over-pressurized - both the oil cap valve and the still existing PCV valve take care of evacuating gases. It’s confusing to me, I guess: one guy will tell you you need vacuum to pull the gases out of the crankcase; another says that the “positive pressure” pushes the gases out via the PCV just fine without a vacuum needed. I am happy that I at least do not have any oil or gases being re-burned and coking up my valves. But, I would like to be sure that blow-by is being cleared completely out of the crankcase. One idea I read about that seems easy is to run the PCV line to the bottom of the air filter box, thereby utilizing a small amount of vacuum for pulling gases out of the cc, and allowing that small amount of gases to be filtered before re-entering the clean air intake and throttle body. Of course, a catch can would be used in line to trap the oil and water. Also, I think the longer hose length will help the oil to not roll all the way to the air filter box. Also, this would require a sealed air filter box (I have an S&B CAI, so it’ll work). Lots of decisions! But luckily there’s also lots of room for experimenting. I’d love it to be as simple as using the vacuum pump for PCV, but I’m thinking that the vacuum pump must have an outlet for unused air, and it’s probably directed back into the engine, thus perhaps re-adding those gases back into the oil. I might just need to be happy with my current setup - at least it removes any chance of all those gases screwing up my valves.

I am very happy with my new-to-me 2015 sierra 1500 (5.3 l) All-Terrain, and especially happy to be back to wrench-twisting a bit on weekends - after I sold my beloved 1973 Ford 3/4 ton 20 years ago, I’ve had only small commuter cars. Since March, I’ve done front/rear gears (4.56s for the 35 inch tires and 8 inch BDS lift), Timbren suspension rear, large capacity transmission pan, new tranny bypass valve, and a few other things. However, from my time on here, I’ve become extremely worried about coking valves, due to the GDI engine. I’m on a quest to make sure that absolutely no unburnt gases, acids, water, etc., ever reaches the back of the valves again. It’s a better engine than the LS, except in this one area, and I think I’ve “solved” the problem, except for one thing: I deleted the vacuum pump, but left it on the block, until I make the next decision - can I route the PCV valve line to the vacuum pump, with a catch can in line between the two, thereby creating vacuum for the evacuation of crankcase gases? I have used the manifold for the brake booster, which gives much better brake response and more constant vacuum, so I need to find a place for the PCV line. Currently, I’m venting under the truck, similar to the old “road draft tubes.” I do have one line still connected from the passenger side valve cover to the CAI tube, so there is plenty of fresh air. I just want a better source of vacuum for the PCV valve, for the health of the engine. Is this something that could be done safely?

Thanks again! (Hmmm . . . Now to decide what to spend the money on instead. This could become addictive - I’m glad I’ve switched to GM after 30 years innFords!)

Thanks for this. As I alluded in my comment, I am a bit concerned about winter. Even though where I live is mild, we still get below-freezing temperatures fairly regularly. Embarrassingly, the automatic transmission is the one I know the least about - even though my father was an AT specialist (for Ford, but . . . ). He was so busy when I was growing up, taking on side jobs rebuilding transmissions, he didn’t have time to teach much. So, I don’t know how - or even if - ATF can be too cool for the good of the trans. For now, I’m just happy with the results of just replacing a single part - I bored my family last week while on the road trip: I kept pointing at the DIC transmission temperature, amazed that it was 65C, not the usual 88-92C. I had a good transmission cooler as my next job for the truck, but I’m thinking I’ll hold off until winter, just to be sure the fluid does not remain too cool on sub-zero days. I also plan to drive up North in January, to an area that stays under zero all winter, often down into -30C or lower. So, I will definitely have a good idea how to proceed with the trans cooler or not. I am also adding the B&M Hi-Tek deep trans pan this week, which adds 3 quarts to the fluid capacity. I’m not completely sold on that - I think their claims of the efficacy of added fluid volume is valid for their diff covers, but I’m not sure simply adding more ATF to the sumo will lead to much more cooling. But, I bought it anyway, for the drain plug alone. This is a very helpful forum, and I have been reading all of your and others’ solid advice since March, when I got the truck. Thank you!

GM quietly admitted their mistake with the original automatic transmission by-pass valve (thermostat) in 2014-2018 gas trucks. A while back, they replaced the part we all have from the factory, and replaced it with a part that looks identical, but that opens to send fluid to the cooler at a much lower temperature (158F, I think). I did try the “flip the pill” method, which was dead easy, but in my haste to complete the job, I neglected to press the c-clip into its channel fully. Ended up with a few litres of ATF coating my garage floor! In my fury at myself for missing such a simple thing, I got more angry at GM. So, I googled a bit and found the new part (86774933), which my local dealer had in stock. For the cost of a $100 (in Canada, everything costs more) part and minor effort to install, the truck now operates at safe temperatures all the time. Before, the ATF heated to around 195-210 just driving to work (half hour on hilly roads). With the new by-pass, it never gets above 150-155, even during a recent 8-hour drive through mountain passes here in northern BC, fully loaded and - because of 35 inch tires - constantly gearing down early on even small hills, not to mention the many 1-6 km long hills. It only reached 166 a few times, after sitting while I got gas or food. This is the only transmission mod I have, so those lower temperatures are all with just the factory in-radiator transmission cooler, and while driving at the hottest time of year - averaged 90-100 F. I thought I might require a good aftermarket cooler, and was about to order the Mishimoto one, but it’s overkill for now. As any ATF fluid temp/tranny longevity chart shows, fluid this cool prolongs the life of the transmission by app. 40,000 miles. So far, the best thing I’ve done to the truck (2015 AT new to me in March this year).

GM quietly admitted their mistake with the original automatic transmission by-pass valve (thermostat) in 2014-2018 gas trucks. A while back, they replaced the part we all have from the factory, and replaced it with a part that looks identical, but that opens to send fluid to the cooler at a much lower temperature. I did try the “flip the pill” method, which was dead easy, but in my haste to complete the job, I neglected to press the c-clip into its channel fully. Ended up with a few litres of ATF coating my garage floor! In my fury at myself for missing such a simple thing, I got more angry at GM. So, I googled a bit and found the new part (86774933), which my local dealer had in stock. For the cost of a $100 part and minor effort to install, the truck now operates at safe temperatures all the time. Before, the ATF heated to around 195-200 just driving to work (half hour on hilly roads). With the new by-pass, it never gets above 150-155, even during a recent 8-hour drive through mountain passes here in northern BC, fully loaded and - because of 35 inch tires - constantly gearing down early on even small hills, not to mention the many 1-6 km long hills. As any ATF fluid temp/tranny longevity chart shows, fluid this cool prolongs the life of the transmission by app. 40,000 miles. So far, the best thing I’ve done to the truck (2015 AT new to me in March this year).