Suburban 3/4 ton 8.1 tow vehicles

[trimacar]

I’ve loved my 3/4 ton Suburban, 8.1, great tow vehicle.  It’s at 150K miles, considered “low” mileage for such a vehicle. I thought it was my forever tow vehicle, but…

 

Just lucked into the identical vehicle, 2002, with under 100k miles.

 

In the near future, the 2001 will be for sale.  Look up “book” value, and add a 50-100%!  It amazed me…
 

Period reviews of the 8.1 state “it could tow small planets”.  Yep.  Buy horsepower, drive torque, and few engines have the torque curve of the 8.1.

 

Those who know, know, these are unicorns, second biggest engine ever put in a GM car  and only available 2001-2006.

 

2001 on left.

 

Gotta love General Motors.

[West Peterson]

Got two of them as well... well, sort of. 2002 GMC 2500HD longbed pickup with the 8.1, and 2003 Avalanche with the 8.1. I prefer the 2002 because it has the Allison transmission. For some reason the Avalanche doesn't have it. How about your suburbans? Allison?

[39BuickEight]

The 8.1 Suburban, Yukon XL’s and Avalanche’s could not be had with the Allison transmission.  They got the 4L-85E, a slightly beefed up version of the 4L-80E that was behind the 6.0. 
 

The Suburban and Avalanche floors were not tall enough to accommodate the Allison.

Edited August 31, 2023 by 39BuickEight (see edit history)

[CarNucopia]

I've also got an 8.1 in my 2006 Chevy 2500HD. I think this was the only year it was mated with it the 6-speed Allison transmission. The truck is a beast, but a thirsty one. As the saying goes, "it'll pass anything on the road,...but a gas station".

 

The only downside is the 26 gallon gas tank give me range anxiety when I'm towing.

[Marty Roth]

2 hours ago, 39BuickEight said:

The 8.1 Suburban, Yukon XL’s and Avalanche’s could not be had with the Allison transmission.  They got the 4L-85E, a slightly beefed up version of the 4L-80E that was behind the 6.0. 
 

The Suburban and Avalanche floors were not tall enough to accommodate the Allison.

Yes, Joe Vicini (Past AACA Pres and GM Engines expert) told me the same thing.

I wanted my new Suburban with Duramax diesel and Allison transmission. Joe advised me to wait rather than buy in 2000 and 2001, but when the 2002 models were released he told me the Suburban/Avalanche floorpan would not permit the Duramax/Allison - and just go ahead with the 2500 ande 8.1L.

 

We have the 2500 Series 2002 Suburban 8.1L with nearly 200,xxx miles,

and also the  2500 Series 2006 Avalanche 8.1L 4-WD also with nearly 200,xxx miles

 

They both tow great, and there is no replacement for displacement ...

but

our 2000 Excursion 7.3L Turbo Diesel 4-WD is even better, at least in my opinion, and is approaching 400,xxx miles, mostly towing my 30 ft long, 12 ft tall hauler with Cadillac, Packard, Buick inside

[trimacar]

10 hours ago, West Peterson said:

How about your suburbans? Allison?

Well, the question's been answered above, nope!  Nice pair of vehicles, West.  

 

I don't plan on keeping the 2001, it will be for sale in the near future.

 

Thanks dc

8 hours ago, CarNucopia said:

The truck is a beast, but a thirsty one

Yes, one doesn't buy an 8.1 for fuel economy. Mine have the 38 gallon gas tanks, so that hurts at the pump but helps on the road.

 

That engine was still built for a few years after 2006, not available in trucks or Suburbans though, think they used them for motor homes.

[West Peterson]

10 hours ago, CarNucopia said:

I've also got an 8.1 in my 2006 Chevy 2500HD. I think this was the only year it was mated with it the 6-speed Allison transmission. The truck is a beast, but a thirsty one.

 

 

 

 

No, as stated above, it's in my 2002 GMC 2500 HD. 2006 may have been the last year (for a while, anyway), but certainly not the only year.

Also, for the size of the engine, the gas mileage is relatively good. Actually better than the 454 Chevrolets we used to tow with.

[CarNucopia]

1 hour ago, West Peterson said:

 

No, as stated above, it's in my 2002 GMC 2500 HD. 2006 may have been the last year (for a while, anyway), but certainly not the only year.

Also, for the size of the engine, the gas mileage is relatively good. Actually better than the 454 Chevrolets we used to tow with.

I’m pretty sure yours is a 5-speed Allison. 2006 has a 6-speed.

[West Peterson]

I guess I thought they were all the same. I stand corrected.

[trimacar]

6 hours ago, West Peterson said:

I guess I thought they were all the same. I stand corrected.

I didnt know either, wouldn’t feel bad if I were you.  I’ve always paid attention to engine size only! 
 

The 2002 is my fifth suburban, 1-3 had the 454.

 

The 2001 has apparently been sold to a forum member, thanks! His personal inspection will confirm deal.

[CarNucopia]

2 hours ago, trimacar said:

The 2001 has apparently been sold to a forum member, thanks! His personal inspection will confirm deal.

Congrats on the sale. This generation of GM truck seems to have gained in value in the last few years. I'm sure part of it is the supply issue and high prices of new trucks. But beyond this, I think these are the peak of analog trucks before complications like displacement-on-demand and more computer systems. If you read the comments on Bring a Trailer when one is up for auction, there's a lot of love for them. The pre-DEF diesels seem particularly desirable.  This reminds me of something I read a while ago that farmers were opting for older tractors instead of buying new because of the simplicity of repairs.

 

To clarify, my issue isn't the MPG, its the gas tank size.

Edited September 1, 2023 by CarNucopia (see edit history)

[trimacar]

Yes, when I bought my 2001, it was priced about 30% over “book value”, but was in perfect shape with 37k miles.

 

I was trying to use book value for 8.1 3/4 ton while dickering with sales manager, he said “Buddy, there IS no book on these trucks”.

 

As said, great tow vehicles, and unicorns to find a good one these days.

 

 

[EmTee]

Glad to be the new owner of this one! 

 

[BuickTom87]

Just got done putting air bags to prevent sagging for my rear and  extra leaf springs and transmission cooler for my tow rig . 
 

looking to tow more this spring summer . I wanted to bring my car to Hershey but next year. 

[trimacar]

3 hours ago, EmTee said:

Glad to be the new owner of this one! 

 

Wow, that sure looks familiar!  Oh, wait…..

 

Glad it went to a good home.

[West Peterson]

On 8/30/2023 at 11:01 PM, CarNucopia said:

The only downside is the 26 gallon gas tank give me range anxiety when I'm towing.

 

Perhaps the short-box came with a smaller tank, or the newer models came with a smaller tank??? I believe the tanks in both my Avalanche and the long-bed are both over 30 gallons.

[EmTee]

From Edmunds for the 2001 Suburban 2500:

 

 

I calculated 15.3 mpg on my trip from VA to NY at mostly 65 mph.

[charlier]

22 hours ago, BuickTom87 said:

Just got done putting air bags to prevent sagging for my rear and  extra leaf springs and transmission cooler for my tow rig . 
 

looking to tow more this spring summer . I wanted to bring my car to Hershey but next year. 

 

Nice looking Tundra you have there. I have an 2012 Tundra.

 

In case you are not aware, the 2nd generation Tundra has a weight carrying hitch limit of 500 lbs and trailer weight limit of 5000 lbs. In order to attain the Tundra's maximum hitch and trailer limits (approximately 1000 lbs on the hitch and 10,000 lb trailer weight, a weight distributing hitch is required per Toyota.

 

I use a weight distributing hitch with sway control on my Tundra when towing my loaded, enclosed, car trailer (about 6,000 lbs). Never have a problem with sagging or swaying. No airbags or extra springs necessary for me when towing.

[BuickTom87]

Yeah I swapped that out also , running air bags for the rear to prevent sagging as well as added an extra leaf spring . 
 

I just did it for piece of mind . 

[CarNucopia]

5 hours ago, West Peterson said:

 

Perhaps the short-box came with a smaller tank, or the newer models came with a smaller tank??? I believe the tanks in both my Avalanche and the long-bed are both over 30 gallons.

Interesting. I need to get under mine to see if the tank size is due to space constraints. I’d be a happy guy if I could gain another 5 gallons with a swap.
 

 

5 hours ago, EmTee said:

From Edmunds for the 2001 Suburban 2500:

 

 

I calculated 15.3 mpg on my trip from VA to NY at mostly 65 mph.

I couldn’t find the EPA rating for my ‘06. I’d bet the aerodynamics of a Suburban are far better then my truck and account for the 3MPG improvement you have on the highway.

[Marty Roth]

20 hours ago, Bills Auto Works said:

The 8.1 is a good engine & will provided great reliability for hundreds of thousands of miles! 

 

   However in my case being a transporter who gets paid by the loaded mile....I could never use one. My two Duramax diesels (3500 Chevy & 2500HD GMC) get basically twice the fuel mileage of the 8.1 pulling my trailers & will outlast  & out pull the 8.1 easily. They both currently have over 600k each on the original engines & transmissions. They both use less than a quart of oil per 10k miles & are only used with trailers attached.

 

God Bless

Bill

https://www.jalopyjournal.com/forum/threads/nationwide-single-car-transport-hauling-open-or-enclosed.614419/

From 2000 until 2002 I had hoped the 2500 Suburban would eventually be available with the Dura-Max Diesel and the Allison transmission, as suggested by former GM Engines and AACA National President Joe Vicini.

In October, 2001 Joe called me and let me know the floor pan of the Suburban would not be revised to accept that driveline, and to just go ahead with the 8.1L gas engine. It is a fine unit, now with nearly 200,000 miles and no needed repairs (Same configuration in our 2005 2500 Avalanche), but neither have the towing ease of our 400,xxx mile 2000 Excursion 7.3L Diesel.

 

[Robert G. Smits]

1 hour ago, Marty Roth said:

neither have the towing ease of our 400,xxx mile 2000 Excursion 7.3L Diesel.

My 2001 Excursion 7.3 was a great tow vehicle but couldn't touch the 96 Dodge Cummins 12 valve that preceded it.  Finally my bad left knee wouldn't tolerate the the Dodge standard transmission.  In 2007 I upgraded to a Chevy Duramax/Allison which should be my last tow vehicle.  For those of you towing with pick-up consider a 50-70 gal auxiliary fuel tank.  Best towing money I ever spent.  I used to tow with a friend using The 8.1.  All of my diesels would smoke him on upgrades and at the gas station.

[EmTee]

What kind of mileage are people seeing when towing with the Duramax/Allison?  A friend of mine mentioned 14 mpg, but I believe that's pulling an RV trailer of unknown (to me) size/weight.  For the number of miles I'll be towing annually, I think the 8.1 will be fine for me; particularly as a first tow vehicle.  My brother had an F350 crew cab dually with the 7.3 and manual transmission.  He loved it and only sold it when he decided to go with a Class A motorhome.

[Robert G. Smits]

On 9/11/2023 at 7:24 PM, EmTee said:

I think the 8.1 will be fine for me;

You are going to love it.  They are great tow vehicles. Just make sure you use a equalizer hitch.   I think my mileage on the Duramax is around 10-12 towing a 30 ft. GN trailer.  When I haul two cars with the 48 ft. it drops below 10.  Mileage is so dependent on towing speed.  After a while you get used to paying for 70-80 gal of Diesel each fuel stop.

[EmTee]

21 hours ago, Robert G. Smits said:

You are going to love it.

Hope so -- just bought this today (2023 Pace American 8.5X24 Enclosed Car Hauler)... 

 

[EmTee]

Update on my recently acquired 8.1 Suburban:

 

The 'SERVICE RIDE CONTROL" message has been displayed on the Message Center for quite some time prior to my purchase.  I did not notice any ill-effect with regard to performance or handling, even while towing my 24' enclosed car hauler.  Still, I wanted to determine what was wrong and determine whether it could be fixed at reasonable cost before giving-up on it.  Researching the Autoride system on the internet generally turns up a bunch of posts on various GM truck forums aimed at either replacing the system components with aftermarket non-adaptive shocks or otherwise disabling the stock system in an effort to eliminate the error message.  I did, however, find one posting where someone identified and restored their Autoride by replacing one of the rear height sensors with one from a later-model Suburban ('07).  He then determined that one of the wires in the original sensor's pigtail was open.  He repaired the wire and bench-checked the repair, but didn't reinstall the sensor since he had already modified and installed the new one.

 

That said, my Suburban had a broken link on the RR height sensor.  I was hoping that repairing that mechanical problem would restore operation.  I replaced the broken link with a piece of threaded rod and ball-ends that I found on Amazon.  I cut the rod to match the length of the original link.

 

 

Unfortunately, this repair did not extinguish the error.  Unlike my wife's '93 Allante, the Suburban doesn't provide an embedded electronic diagnostic function to read system error codes and data values.  So, I took it to my trusted local mechanic and he used his Tech II compatible scan tool to obtain the suspension error codes.  There was a single suspension fault (C0625) which identified a problem with the LR height sensor circuit.  We could also see that the LR height sensor was reporting 0 Volts, unlike the others.

 

Armed with that knowledge, once I got home I disconnected the connector at the LR height sensor and verified that 5 Volts was present at the chassis connection (Pin A).

 

 

I then removed the LR sensor and used my Ohm meter to check resistances between pins A&C, A&B and B&C.  There was no continuity between any of the pins.  Normally this would suggest that the sensor (i.e., the variable resistor) is bad, however, based on the internet post identifying a broken pigtail wire mentioned above, I decided to attempt exposing the soldered pigtail connection which is molded to the sensor body.  Going slowly, I was able to expose the sensor terminals and found the wires attached to pin B and pin C were open.  I was able to confirm continuity between A and C at the sensor terminal and variable resistance readings between pins A&B and B&C measured at the sensor terminals as I moved the lever arm.  Next, I disassembled the pigtail harness in order to try to find the discontinuities.  There was no sign of external damage anywhere on the harness and the Weatherpack connector contacts were clean.  Exposing the individual harness wires revealed multiple 'cuts' in the blue wire ( Pin B ) and at least one similar defect on the black wire ( Pin C ).

 

 

The copper conductor at those spots was basically reduced to copper-oxide dust.  I have no explanation for how this happened, however, as there was no external harness damage and no obvious evidence of moisture or contamination.  It seems to be the result of a wire manufacturing defect.  Even though the red wire ( Pin A ) looked OK and was still functional, I decided all three needed to be replaced, given the condition of the other two.

 

I proceeded to fabricate a new pigtail using similar gauge wire that I had on-hand.  After soldering the wires to the terminals at the sensor end, I did likewise at the connector pins.

 

 

I twisted and bundled them as the originals were and wrapped them with self-vulcanizing electrical tape.  I potted the soldered connections at the sensor using RTV silicone.  Once the RTV had cured I wrapped that area with the same self-vulcanizing tape.  I then wrapped the entire pigtail in electrical tape and applied the original split corrugated  plastic wire conduit.

 

 

After a final wire check I re-installed the sensor on the truck and went for a test drive.  Here's the result:

 

 

I want to say that the ride (empty) did seem to feel a bit 'softer' now, but I could be imagining that...  Good news is the Message Center is clean now, so the system is 'happy'.  We'll see how long it lasts, but at least this proves that the system can work and the repair doesn't have to be expensive.  Now, I have the time to spend on projects like this, so fixing these wires wouldn't be cheap if I had to pay someone else to do it.

 

The key discoveries I made while doing this were: (1) the rear height sensor pigtail can fail while the sensor mechanism is intact and (2) there were no servo faults being reported by the shock absorbers on my Suburban.  If one or more shocks had been faulted, then either retrofitting manual shocks or electrically disabling the system would have been the only remaining options.

 

As a last word, I'll note that the Autoride system on the 8.1 Suburban seems to be a later evolution of the Road Sensing Suspension (RSS) on my wife's 1993 Allante'.  That car uses Linear Variable Differential Transformer (LVDT) height sensors at each wheel, as opposed to the variable resistors on the later Cadillac and Suburban Autoride system.  The Allante' has a bad LF height sensor which is no longer available (even used).  The Autoride sensors seem to be a more robust design.  The early ('01 - '06) Suburban rear height sensors are no longer available, but as I found online, the '07 sensor can be used, but requires fabricating a connectorized pigtail, as the later design is like the '01 - '06 front sensors which plug directly into the chassis harness without their own pigtail.  I bought two new front height sensors for the Suburban just to keep on the shelf since they are available now at reasonable cost (~$35 ea.).  If push comes to shove, I think I could remove the electrical sensor from one of the new front assemblies and attach it to a rear mount to replace a bad rear sensor.

[EmTee]

Thanks Bill, I have only made one long trip with the Suburban so far and averaged 9 mpg overall from NY to GA and back.  That's what i expected based on what the PO told me.  The more I drive this Suburban, the more I like it.  Its condition is so good overall that I didn't want to just give up on the Autoride without first determining what was wrong with it.

 

As for the Duramax, the day I took the Suburban to my mechanic's shop to have the suspension codes read, he had his GMC 2500 HD Duramax in the shop with the hood open.  I said "Oh - Oh, this can't be good!"  He was just finishing-up replacement of the diesel fuel pump and injectors.  Apparently this is a known issue with them.  He has had the truck a few years and bought it with 70K miles.  I think it has a bit less than 150K now.  I asked him about the cost and he said his price for the parts was close to $4K total!  Apparently when the fuel pump fails it can send shrapnel through the rest of the system and the amount of effort involved to fix it is such that he didn't want to risk having to do it again, so he did as GM recommends and replaced everything downstream.

 

That situation confirmed my assertion that for many old car hobbyists, a big-block gas engine (e.g., 454/496) can make sense.  I can maintain my Suburban myself and parts are widely available at reasonable cost.  The better diesel mileage is offset by the higher price of fuel (about $1 per gallon more than gasoline) and higher repair cost for the diesel.  My situation, towing only 3 ~ 5K miles per year, is a lot different than that of someone like you who does it for a living.

[EmTee]

21 hours ago, Bills Auto Works said:

Sounds like his Duramax is newer than either of mine.

Yes, it's newer and uses DEF.  I don't know the specific year, but I'm guessing it's a later teens model.  Thanks, I'll definitely tell him about the Fass system.