Chevrolet Suburban 3500 Questions

[Geotrash]

Just a pic from the weekend and a few observations:

After towing the camper out past Charlottesville, plus a bunch of driving around before and after, I was down to 1/4 tank, and filled it with 87, just to see how it would perform. I had previously filled it with 93, so I thought it would be illustrative. And it was. I had a much harder time holding 5th on the way home running 87 than I did on the way out there running 93, despite having a tailwind vs a headwind previously. While it's not a scientific test, I conclude that while the L96 can safely run 87, its power output under high loads increases with 93.

Second, this thing really is a marvelous towing platform. I could set the cruise and it would hold 65 all day long, pulling that camper, if I wanted it to. The seats are very comfortable for my wife and me, and the ride is amazing for a 1-ton SUV. It's definitely not as smooth as our Denali's with Autoride, but it's smooth enough to not induce dread at the prospect of a long drive.

Third, cooling seems to be more than adequate. On my 6.2L Yukon XL's, transmission temps can get a little higher (up to 210ºF) climbing the west side of Afton mountain on 64, with engine coolant temps getting up to 230ºF on hot days. With the Suburban 3500, the hottest transmission temp I saw on that same grade at 90ºF ambient, was 190ºF, going right back down to 170ºF after cresting the hill. Coolant temp never even budged. Very impressed.

Also, as expected, there were some keen eyes in the campground who stopped to inquire, having never seen an 8-lug K2 Suburban.

 

[Geotrash]

Today's task: replacing the original batteries over lunch. Although most auto parts store configurators showed only the 94R battery for this rig, it actually has two different batteries. A size 94R and a size 48, from the factory. Walmart was out of stock on the Platinum (AGM) for both, so I went with the regular lead-acid Everstart Maxx with the 3-year warranty. Pics when I complete the job.

 

[Geotrash]

Had to work fast because I only had 30 minutes, so these are the only pics I got. For anyone who has to change out the larger battery on the pax side back by the firewall, the trick is to flip it on its side counterclockwise (facing it from the front of the truck) before taking it out so it will clear the coolant recovery tank without the need to remove it first. Naturally, you'll need to remove the brace that crosses the battery diagonally between the fender and the firewall. You'll need a 10mm for the terminals, and a 13mm deep well for the battery cable at the bus, and a 13mm with an extension for the brace and battery hold-down bolts.

These were the originals and they were definitely conventional lead-acid batteries.

 

[Bigburb3500]

@Geotrash, will you be doing the add a transmission dipstick modification? I think this is something I am going to do and the 6L90 should be easy?

Also, have been messaging with several major lift companies, no one supports our truck for aftermarket. Might be limited to stock replacement shocks but will let you know what I find. My goal is to do a 2-3” lift + airbag helpers in the rear.

 

[Geotrash]

@Geotrash, will you be doing the add a transmission dipstick modification? I think this is something I am going to do and the 6L90 should be easy?

Also, have been messaging with several major lift companies, no one supports our truck for aftermarket. Might be limited to stock replacement shocks but will let you know what I find. My goal is to do a 2-3” lift + airbag helpers in the rear.

Yes, I plan to do the dipstick mod in the fall when I can stand being in the garage for more than 15 minutes. I have all of the parts in my Scamazon shopping cart.

On the lift, I plan to keep mine stock height but may upgrade the shocks. I would think that lift kits for 3500 SRW pickups should work with ours since it's the same frame and running gear, but I don't know for sure. And, I'm told that the Billstein 4600 is one of the best choices for replacement shocks when that time comes.

 

[Geotrash]

On another topic, does anyone know if the 6L90 in the 2018 Suburban 3500HD has the thermostat for the oil cooler? Is so, can I use the same Transgo kit to bypass it as they use in the 6L80's?

@NickTransmissions

 

[Bigburb3500]

Yes, I plan to do the dipstick mod in the fall when I can stand being in the garage for more than 15 minutes. I have all of the parts in my Scamazon shopping cart.

On the lift, I plan to keep mine stock height but may upgrade the shocks. I would think that lift kits for 3500 SRW pickups should work with ours since it's the same frame and running gear, but I don't know for sure. And, I'm told that the Billstein 4600 is one of the best choices for replacement shocks when that time comes.

Great! I am in the same boat haha and will probably do it after a few more trips I have planned

So I’m not 100% sure… I think the front end is a mix of pickup HD and previous gen-2500 Suburban. I would GUESS a lot of stuff is interchangeable but have not dug enough to confirm. I do know the rear is different as the axle housing is different but same guts. Thank you for asking about the trans term - that’s on my review list too.

Quick google of stock replacement part shows the same shock is used on previous gen 2500 Burb and two-gen previous Silverado HD. I wonder if any “stock” replacement shock can be used, I may at minimum do King/Fox bypass adjustable shocks.

 

[Doubeleive]

On another topic, does anyone know if the 6L90 in the 2018 Suburban 3500HD has the thermostat for the oil cooler? Is so, can I use the same Transgo kit to bypass it as they use in the 6L80's?

@NickTransmissions

same for all, this is what I put in the wifes 16

TransGo Cooler Flow Bypass Kit 6L80 6L90 8L90 10L90, 6L80-CLR-BYPASS | eBay

Cooler Flow Bypass Delete Kit Fits 2014-on 6L80, 6L90, 2015-on 8L90, 2017-19 Allison An easy, no-hassle cost-effective drop-in Cooler Flow Bypass Delete Kit for General Motors 6L80, 6L90, 8L90 and Allison transmissions. Corrects/Prevents/Reduces: ---Provides all-time cooler flow regardless of...

www.ebay.com

 

[strutaeng]

Yes, I plan to do the dipstick mod in the fall when I can stand being in the garage for more than 15 minutes. I have all of the parts in my Scamazon shopping cart.

What is the dipstick mod?

 

[Bigburb3500]

What is the dipstick mod?

Newer trans doesn’t not have a dipstick. We are both planning to add what GM should have included.