2012 4.8L GMC Sierra Towing Capacity

Richdem · July 16, 2018

Hello,

I am looking at purchasing a used 2012 GMC Sierra 1500 SL Ext Cab 4WD 4.8L V8 (Standard Box)

The main purpose of this truck will be to tow our 19FT Travel trailer which has a max weight of 4,700 lbs. I have done some research and from the RPO codes in the glovebox I found it has an axle code of 3:42 which gives a towing capacity of 5,500 lbs.

Would anyone be able to confirm if this is correct, I was quite surprised as it seems very low for a full size pickup. I am sure the V8 can handle this. Currently the trailer weighs 4,160lbs (I put it on a CAT scale this last weekend) so I have another 500 lbs that I could technically add to it but with passengers, cargo etc in the truck that will put me very close if not over the max capacity for the truck.

Thanks in advance for any help or advice

Richard

newdude · July 16, 2018

Numbers are right. The 4.8 can probably handle it. Its the gearing and transmission combo that hurts you. 4L60 and the 3.42 gears produce much lower overall gearing than other combinations. If it was a 5.3 and 3.42 gears, that would have had the 6 speed, which offers a whole 2 extra gears and much steeper starting ratios, you'd be up to 9600lbs. If your 4.8 had 3.73 gears, you'd be at 6500lbs or so, but GM only ran those on 2wd for that year.

I'd try to keep the trailer at or under 4500lbs.

If you look at the tire sticker (white and yellow) on your driver door jamb, what does it say for the truck's payload?

Also on your RPO label, do you show option KNP on there?

Edited July 16, 2018 by newdude

redvett · July 16, 2018

I would keep looking for a truck with tow pkg and the equipment to haul your trailer. The truck you are looking at will be marginal at best because its easy to overload with the margin you would have and safety and reliability will be compromised.

swathdiver · July 17, 2018

4 hours ago, Richdem said:

Hello,

I am looking at purchasing a used 2012 GMC Sierra 1500 SL Ext Cab 4WD 4.8L V8 (Standard Box)

5,500 pounds and a GCWR of 11,000 pounds.

Same truck with a 5.3 and K5L = 9,600 pounds and GCWR of 15,000 pounds.

Richdem · July 17, 2018

This is exactly what I thought,

Thank you so much for the quick replies. I have learn't a lot about shopping for trucks over the last little while lol

I will keep looking for a 5.3 V8, I know it is overkill for our trailer but I will be happy knowing I can load both truck & trailer without worrying if I am close to the limits

Richdem · July 17, 2018

4 hours ago, newdude said:

Numbers are right. The 4.8 can probably handle it. Its the gearing and transmission combo that hurts you. 4L60 and the 3.42 gears produce much lower overall gearing than other combinations. If it was a 5.3 and 3.42 gears, that would have had the 6 speed, which offers a whole 2 extra gears and much steeper starting ratios, you'd be up to 9600lbs. If your 4.8 had 3.73 gears, you'd be at 6500lbs or so, but GM only ran those on 2wd for that year.

I'd try to keep the trailer at or under 4500lbs.

If you look at the tire sticker (white and yellow) on your driver door jamb, what does it say for the truck's payload?

Also on your RPO label, do you show option KNP on there?

I will have another look, What does the KNP mean ?

swathdiver · July 17, 2018

KNP is an RPO code for the factory external transmission cooler. I think he meant K5L which is the Enhanced Cooling Package which includes KNP, KCP (Engine Oil Cooler). You might also look for JL1 which is the Integrated Trailer Brake Controller, nice but not essential. You'll also want a 3.42 gear at minimum and the 6-speed transmission is great.

Richdem · July 17, 2018

8 minutes ago, swathdiver said:

KNP is an RPO code for the factory external transmission cooler. I think he meant K5L which is the Enhanced Cooling Package which includes KNP, KCP (Engine Oil Cooler). You might also look for JL1 which is the Integrated Trailer Brake Controller, nice but not essential. You'll also want a 3.42 gear at minimum and the 6-speed transmission is great.

I have been talking to a very nice lady that has a mint 2012 Sierra it was all going well until she told me it has the 4.8L V8. It does have the Tow/Haul button on the gear shifter and she was kind enough to send me a pic of the page from the manual which shows the 4.8L V8 has either 3.23 or 3.73 axle ratio along with the RPO sticker. I saw GU6 which I thought was 3.42.

I have included the 2 pics, Am I reading the RPO sticker correctly?

8 minutes ago, swathdiver said:

swathdiver · July 17, 2018

Yep, this one has a 3.42 gear (GU6) and the external transmission cooler (KNP) by itself. She's on the wrong page, a K10753 is an 4WD Extended Cab with a Regular Bed. Tow ratings are the same, 5,500/11,000.

Good things about this truck is that is a simple truck, not a lot of bells and whistles to go wrong and the motor (L20) does not have AFM. Put a 3.622 crankshaft in it and it becomes a 5.3!

The L20 does not have AFM, does have VVT and is FlexFuel capable.

Edited July 17, 2018 by swathdiver

cire0309 · July 17, 2018

4 minutes ago, swathdiver said:

Yep, this one has a 3.42 gear (GU6) and the external transmission cooler (KNP) by itself. She's on the wrong page, a K10753 is an 4WD Extended Cab with a Regular Bed. Tow ratings are the same, 5,500/11,000.

Good things about this truck is that is a simple truck, not a lot of bells and whistles to go wrong and the motor (L20) does not have AFM.

Definitely. A simple Vortec 4.8 without the AFM crap. Although the 4L60 leaves a lot to be desired.

Richdem · July 17, 2018

9 hours ago, swathdiver said:

Yep, this one has a 3.42 gear (GU6) and the external transmission cooler (KNP) by itself. She's on the wrong page, a K10753 is an 4WD Extended Cab with a Regular Bed. Tow ratings are the same, 5,500/11,000.

Good things about this truck is that is a simple truck, not a lot of bells and whistles to go wrong and the motor (L20) does not have AFM. Put a 3.622 crankshaft in it and it becomes a 5.3!

The L20 does not have AFM, does have VVT and is FlexFuel capable.

So would it be wise to continue the search for a 5.3? This lady is the original owner and the truck only has 152,000 KM's (I forgot to mention I was in Canada)

Our travel trailer is 19FT and it's GVWR is 4,700 lbs, currently we are at 4,160 lbs. When we weighed it the only thing missing was the food we take away with us. I will also be using a Husky weight distribution hitch & sway bar

newdude · July 17, 2018

11 hours ago, swathdiver said:

KNP is an RPO code for the factory external transmission cooler. I think he meant K5L which is the Enhanced Cooling Package which includes KNP, KCP (Engine Oil Cooler). You might also look for JL1 which is the Integrated Trailer Brake Controller, nice but not essential. You'll also want a 3.42 gear at minimum and the 6-speed transmission is great.

K5L is on the 5.3. KNP standalone is on the 4.8.

swathdiver · July 17, 2018

4 hours ago, Richdem said:

So would it be wise to continue the search for a 5.3? This lady is the original owner and the truck only has 152,000 KM's (I forgot to mention I was in Canada)

Our travel trailer is 19FT and it's GVWR is 4,700 lbs, currently we are at 4,160 lbs. When we weighed it the only thing missing was the food we take away with us. I will also be using a Husky weight distribution hitch & sway bar

How much would that truck weigh with you and your family in it and the stuff that wouldn't be in the TT? You may also run up against the 11,000 pound GCWR limit. I have no direct experience with that truck/engine but would want the biggest margins I could afford. That engine doesn't look too much smaller power wise compared with the 5.3 but it makes its power higher in the rpm band, it will really work in the hills and mountains, probably have to stay in 3rd most of the time. Hope some other fellas will chime in who know this truck better.

Richdem · July 18, 2018

8 hours ago, swathdiver said:

How much would that truck weigh with you and your family in it and the stuff that wouldn't be in the TT? You may also run up against the 11,000 pound GCWR limit. I have no direct experience with that truck/engine but would want the biggest margins I could afford. That engine doesn't look too much smaller power wise compared with the 5.3 but it makes its power higher in the rpm band, it will really work in the hills and mountains, probably have to stay in 3rd most of the time. Hope some other fellas will chime in who know this truck better.

You are absolutely right, I am just pretty shocked that the 4.8L V8 only has a towing capacity of 5,500 lbs in that configuration. I will keep searching for a decent 5.3 Sierra or Silverado. One thing for sure is that I have learnt a fair bit about how these trucks are configured from the factory. I never knew it would be so involved lol

CapitalTruck · August 2, 2018

I had an 04 4.8 2wd Ext Cab 4L60E with 3.73. It had a tow capacity of 7100. I towed a 6500 pound boat from Delaware to Corpus Christi Texas. It was third gear pretty much the whole way. Those Tennessee mountains were a 2nd gear hazard flasher operation. It made the trip with no problem (I had added an auto trans cooler before the trip). However, I would recommend a greater margin of safety than what you're mentioning. With the 3.73 you'd probably be okay, but with that 3.42, forget it. I have a 13 with 4wd ext cab 4.8, it is listed at 5500. I have come close to that and I sure wouldn't want to do it for long term.