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Started By
Message
GMT800 2500 Suburban/Yukon XL 6.0 v 8.1?
Posted on 12/4/25 at 10:57 am
Posted on 12/4/25 at 10:57 am
Facebook Marketplace algorithms must be dialed in to me cause I keep seeing nice clean GMT800 2500 Suburbans at great prices and now they have piqued my interest. Mainly want it for medium duty bumper pulling around 5-8klbs either my little 4klbs travel trailer or 8-9klbs loaded car hauler with either a TJ/JK or FZJ80 cross country to the west coast for 4x4 trips which is a once every 2 years type of trip. But if it could pull the car hauler and the 4x4 I would probably use it more for local off road trips here in the SE.
I currently use a 1st gen Sequioa which is OK with the 4k travel trailer at least around here in the flattish SE terrain but isn't suitable for towing the car hauler. Would be a daily driver though I don't really drive much as I work from home. Most of the miles on my sequoia are from big long trips off roading and mountain biking.
Feels like the 6.0 would be great for 99% of my driving have a ton of aftermarket support and parts availability and better gas milage but then I think about that drive out west and that big 8.1 might be real nice when pulling 8k lbs across the rockies and sierra nevada mountains. Maybe the 6.0 is good enough? Would love to hear some feedback to those of you who had both.
I currently use a 1st gen Sequioa which is OK with the 4k travel trailer at least around here in the flattish SE terrain but isn't suitable for towing the car hauler. Would be a daily driver though I don't really drive much as I work from home. Most of the miles on my sequoia are from big long trips off roading and mountain biking.
Feels like the 6.0 would be great for 99% of my driving have a ton of aftermarket support and parts availability and better gas milage but then I think about that drive out west and that big 8.1 might be real nice when pulling 8k lbs across the rockies and sierra nevada mountains. Maybe the 6.0 is good enough? Would love to hear some feedback to those of you who had both.
2
Posted on 12/6/25 at 5:38 pm to DeoreDX
Never owned either but work with guys that do, both in 3/4-ton trucks and the 8.1L seems to be the consensus winner. Gas mileage isn't much of a difference unloaded but the 8.1 tows better at any weight. I think the 8.1 got bolted to a different transmission in non-truck applications, 4L85E, which would be a little upgrade over the 4L80E that backs the 6.0's.
Posted on 12/6/25 at 11:08 pm to Clames
6.0 header bolts can snap at the block and the steam cam make a tick sound.
Have to remove the headers to get the bolts out.
They made upgraded bolts for it
Have to remove the headers to get the bolts out.
They made upgraded bolts for it
Posted on 12/6/25 at 11:28 pm to Clames
quote:
think the 8.1 got bolted to a different transmission in non-truck applications, 4L85E, which would be a little upgrade over the 4L80E that backs the 6.0's
The 8.1 has an Allison 6 speed in the 2500HD trucks. Not sure of that was ever available on the Suburbans.
If so, go find an 8.1 Allison.
This post was edited on 12/6/25 at 11:30 pm
Posted on 12/7/25 at 7:40 am to Clames
quote:
I think the 8.1 got bolted to a different transmission
Correct, it did. But not an Allison transmission. The 8.1L Vortec in a Suburban is typically paired with the heavy-duty 4L85E transmission from the manufacturer, not the Allison, as the Allison's larger size generally requires body modifications (like a body lift) to fit the Suburban's transmission tunnel…
Posted on 12/7/25 at 8:02 am to DeoreDX
quote:
Feels like the 6.0 would be great for 99% of my driving have a ton of aftermarket support and parts availability
Yep. The 6.0 is awesome. They are thirsty but indestructible. Bazillion of them still running around.
The 8.1 is far, far cooler. Unloaded mpg wont be much different if at all. 8.1 will probably burn a little oil, nothing to worry about. If you can find a non clapped out 8.1, buy it. I wouldnt pass on a good 6.0 though.
Posted on 12/7/25 at 11:12 am to RichJ
4L80E is a solid transmission so I would suspect the 4L85E would be perfectly fine for what the OP wants to do. I would upgrade the transmission cooler, see if there is a deep sump transmission pan available with a drain plug, and do a dump/refill every 30k miles of the ATF.
Posted on 12/7/25 at 11:16 am to Clames
quote:
do a dump/refill every 30k miles of the ATF.
Screw that. My old 4L80e lived over 250k miles on the factory fill and it had been literally worked to death.
Once every 100k fluid changes would be plenty good on those hydromatics.
Posted on 12/7/25 at 11:43 am to DownshiftAndFloorIt
Speaking if that what is your take on changing transmission fluid. My 16 GMC is about due for the 2nd change since the rebuild. Do them evey 25K miles or so. Well the last guy I brought it to said not to do a change, because it will pull more material off the plates and cause it to start slipping.
Posted on 12/7/25 at 11:54 am to GREENHEAD22
I think tranny fluid is every 50-60K, not every 25. I've heard some mechanics say changing the fluid too often actually actually bad.
Posted on 12/7/25 at 12:10 pm to GREENHEAD22
It isnt possible to do it too often assuming its done correctly. Its just a pain in the arse to do properly so I dont do it more than I have to.
Stick to whatever the factory recommended change interval is for commercial usage and itll be good unless you have a specific reason to change it more often. For instance I have a 68RFE in my truck - veritable hunk of shite thats hard on fluid. I change it at ~ 80k vs factory recommended 120k.
Ive heard this plenty of times before. From an engineering perspective it makes zero sense. If a transmission starts slipping right after a fluid change it was either put back together wrong, wrong fluid was used, or it was wrecked already before the change. They only slip from low apply pressure or exceeding the torque limits. Fresh fluid makes clutches more grabby, not more slippery.
Stick to whatever the factory recommended change interval is for commercial usage and itll be good unless you have a specific reason to change it more often. For instance I have a 68RFE in my truck - veritable hunk of shite thats hard on fluid. I change it at ~ 80k vs factory recommended 120k.
quote:
said not to do a change, because it will pull more material off the plates and cause it to start slipping.
Ive heard this plenty of times before. From an engineering perspective it makes zero sense. If a transmission starts slipping right after a fluid change it was either put back together wrong, wrong fluid was used, or it was wrecked already before the change. They only slip from low apply pressure or exceeding the torque limits. Fresh fluid makes clutches more grabby, not more slippery.
Posted on 12/7/25 at 12:36 pm to GREENHEAD22
quote:
Well the last guy I brought it to said not to do a change, because it will pull more material off the plates and cause it to start slipping.
That's bullshite. The additives, like friction modifiers, that get used up as transmission fluid ages, is what keeps the transmission from slipping. Friction material from the clutches and steel particles from the plates and other parts get filtered out or settle in the bottom of the pan (and get stuck to the magnet if there is one) are not contributing to the transmission shifting properly. Replacing the fluid regularly keeps the active additives from getting depleted to a point that things start to slip. Same for engine oil.
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