GM 5.3 vs. 6.0 mileage?

[daveinnh]

I have a 2002 Chevy 1/2 ton extended cab w/ the 5.3 engine. It's been fine, but I now have over 160k miles and need to replace before repair bills arrive. (advice by my local mechanic)

I see GM has something called "active fuel management" - a business contact bought a 2007 Avalanche (sp?) with the 5.3 and complained that it only operated in the 4-cyl mode when going downhill. He wishes for the 6.0.

Thoughts with mileage in mind?

[asylum575]

I have a 3/4 ton with the 6.0 and 4 spd automatic. 2006 model year. I get between 10-12MPG. In 2007 they added a new 6 spd, not allison to the 6.0. Should do a little better. The 5.3 does much better. The 6.o is the best gas tower GM makes, they got rid of the 8.1/allison combo. Nobody is looking at diesels these days. Big upfront cost and more at the pump.

[JDPN]

With the AFM, as soon as you stomp the gas all 8 cylinders should engage.

[john_bud]

I didn't think that the 2500 HD was getting the active fuel management.

Could you double check that and post back (as I'm too sleepy and lazy to check myself).

jb

[asylum575]

I don't think the HDs are getting AFM, that's why they got a 6 spd.
I think by 09-10 all the 4.8s and 5.3s will be matched to a 6 spd also. I don't know if the 6 spd will have AFM those engines. The carmakers have to improve MPG across the board in the next 5-10 years by act of congress.

[zzvyb6]

My Tahoe has AFM and it runs 4 cyl on level roads even pulling the boat. You can feel it jump into 4 cyl. You need to avoid cruise control for bets economy with this system. I had a 6L Yukon XL as a company provided vehicle with the 6 speed. It did Not have AFM but it was easy to get 22-23 mpg for same loads once it gets into 6th gear. The problem I had was the fun of stomping on the pedal. With the high torque, I could dust off anything. I now have a company provided Avalanche with AFM. (I change vehicles every 3 months). This gets 22-23 with AFM on gas just like the Tahoe. Lately I've been running ethanol in it for testing and the mileage is 2/3 of that number. The only way you can tell what fuel is in it is by the idle exhaust smell. Ethanol has a sweet smell.

[john_bud]

I think the 6.0L is available with AFM in the 1500, but NOT in the 2500HD for some reason.

The 1500 has an aluminum block 6.0L where the 2500 is iron block.

[Z-Michigan]

AFM is only on the light duty ("1/2 ton" aka 1500 series) trucks. I have it in the 5.3L in my 2007 Suburban. It comes on a lot and I get good mpg for such a large vehicle; 16-17mpg in commuting, best ever tank of 20.6 on the freeway, and 18+ is reasonably common in highway travel. It is not intrusive and all 8 cylinders are there whenever you push the pedal.

All depends whether you need a heavy duty truck or if a 1/2 ton will do what you want.

[jimmysisson]

So are these AFM engines too new to have reliability records? How does it shut down the cylinders? GM has been down this road before with the Caddy with nobody too pleased, as I remember it.
Jim

[Z-Michigan]

The engines have hydraulic lifters, like most engines. The system shuts off oil flow to half those lifters, so the valves stay closed (both intake and exhaust valves on 4 cylinders). The switchover time is supposed to be 0.040 second each way.

Not sure but I think this system debuted in GM vehicles with the 2007 Suburban/Tahoe that came out originally in mid to late 2006. I have one, have 10k miles, no problems. I have not heard of any problems. Chrysler has a nearly identical system on the Hemi V8, and I think its deactivation system was introduced in 2005. Again, no problems, though that one can be damaged if you use a heavier oil than spec. Honda and Mercedes have been using somewhat similar systems for longer than that; my 2004 Honda Civic Hybrid had a full shutdown system when braking. I believe it was introduced in 2003 or so, and again I have not heard of any problems.