04 Tahoe 20mpg goal

[Andrewhans]

Originally Posted by darcane

At 285hp for the 4.8L vs 295hp for the 5.3L, I was fine with the smaller engine. They are pretty close in performance, with a slight edge in power for the 5.3 and economy for the 4.8. In spite of the high gears, it tows our 4500+ lb travel trailer just fine.

I'm probably mistaken on the cooler then. Neither my old Silverado nor the Tahoe have the other cooler you are referring to behind the emblem and neither have tranny temp sensors. As long as you are monitoring the temps, you should be fine.

From memory, both my Silverado and Tahoe have the slots completely open, with flaps behind it that deflect air towards the radiator. I'll double check on the Tahoe tonight.

I understand not wanting to alter the looks. My wife tolerates it on my Civic but will raise hell if I touch her Tahoe.

My gauge cluster does not have a trans temp gauge on it either. I use Torque for that. Both of your vehicles do have trans temp sensors from the factory, the computer will change shift patterns based on temp as you warm up the vehicle. You just need to be able to access them and monitor them.

My vehicle has the tow package as well so I have the trans/powersteering cooler. If yours doesn't have the aux cooler directly behind the emblem your trans cooler is simply part of the radiator, as is standard on these trucks.

The only thing I wanted different on mine is 2WD vs AWD. I would easily be averageing 17.5 to 18.5 per tank instead of struggleing to get 17.5.

Once winter hits and I put my grill block back on and do the belly pan I should be hitting 18 per tank... hopefully.

[darcane]

Originally Posted by Andrewhans

My gauge cluster does not have a trans temp gauge on it either. I use Torque for that. Both of your vehicles do have trans temp sensors from the factory, the computer will change shift patterns based on temp as you warm up the vehicle. You just need to be able to access them and monitor them.

My vehicle has the tow package as well so I have the trans/powersteering cooler. If yours doesn't have the aux cooler directly behind the emblem your trans cooler is simply part of the radiator, as is standard on these trucks.

The only thing I wanted different on mine is 2WD vs AWD. I would easily be averageing 17.5 to 18.5 per tank instead of struggleing to get 17.5.

Once winter hits and I put my grill block back on and do the belly pan I should be hitting 18 per tank... hopefully.

You've got me second guessing everything I thought I knew about these trucks.

My old Silverado definitely had the bumper slots open, and a coworker's truck ('06) is the same way. Our Tahoe has them covered with thin pieces of plastic. Never noticed that before.

Neither my Silverado nor my Tahoe have factory tow packages and don't have the auxiliary cooler in front of the radiator. I use an UltraGauge to display additional gauges that are not on the OEM dash, and neither displayed tranny temp. I took this to mean the sensor wasn't there...

After looking into it further, tranny temp is not a standardized output through the OBDII port, and because the output is proprietary to GM, my basic UltraGauge can't display it, I would need the programmable variety (UltraGauge MX). You use the Torque app, does it show tranny temp?

Have you figured out how you are going to construct your belly pan?

[cosmick]

The AWD must be costing you a lot more than you think.
I had an '06 GMC Sierra C1500 WT, so 4.3L, 4L60E, 3.23:1, and 245/70R17s. Even with lowering and a tonneau, nothing i tried ever got it over 20 mpg until, i stopped caring about MPG be ause i suddenly needed better towing. I swapped a 4.10:1 axle, got the PCM reflashed, and had no difficulty seeing 22 MPG. For MPG I would have tried a 3.73:1 after that. My similar 94 came with 235/75R15s and a 3.73:1 axle, and was the old TBI, so swirl-port heads rather than the Vortecs, but regularly did 23 MPG stock, and more than once hit 26.
You should actually have less aero drag than my 06, didn't read which engine you have, nor axle ratio, nor tire size, but with a 4.8 and 3.73s you should see 23 if you were 2wd, and you may want to try removing the front shafts until winter. With a 5.3 a 3.42 gear should also do 23.
Doing a cam isnt cheap, the cam alone is 400, plus gaskets, labor, and a tune, at minimum, and you should do valve seals and valvesprings, but would make a dramatic improvement, especially in low RPM torque.

[Andrewhans]

Originally Posted by cosmick

You should actually have less aero drag than my 06, didn't read which engine you have, nor axle ratio, nor tire size, but with a 4.8 and 3.73s you should see 23 if you were 2wd, and you may want to try removing the front shafts until winter. With a 5.3 a 3.42 gear should also do 23.

I think the AWD is costing me a lot but I have no way to confirm it. I can't remove the front shafts because the transfer case has a viscous coupling with a 40/60 split to it. Without the front connected the transfer case would burn up within a mile or two. I have seriously thought about buying a used 4x4 transfer case, installing it and just making it stay in 2wd.

5.3 engine, 3.73 front and rear, 275/55/20 tires. The wheels are 20x9's which is a factory tire/wheel combo on newer GMC Sierra's.

[Andrewhans]

Originally Posted by darcane

You've got me second guessing everything I thought I knew about these trucks.

My old Silverado definitely had the bumper slots open, and a coworker's truck ('06) is the same way. Our Tahoe has them covered with thin pieces of plastic. Never noticed that before.

Neither my Silverado nor my Tahoe have factory tow packages and don't have the auxiliary cooler in front of the radiator. I use an UltraGauge to display additional gauges that are not on the OEM dash, and neither displayed tranny temp. I took this to mean the sensor wasn't there...

After looking into it further, tranny temp is not a standardized output through the OBDII port, and because the output is proprietary to GM, my basic UltraGauge can't display it, I would need the programmable variety (UltraGauge MX). You use the Torque app, does it show tranny temp?

Have you figured out how you are going to construct your belly pan?

The Tourque app does display trans temp for my trans. I keep a sharp eye on it all the time since it's the main killer of the 4l60e trans.

For the belly pan I want to do either coroplast or large black abs sheet. Maybe 1/16" or 1/8". If there are ideas of materials that easy to procure locally that may work better I'm open to ideas.

The big areas I want to hit are the running boards, the front area aft of the OEM air dam, and most of the center. Leaving room for exhaust heat to escape and for servicability. I will take pics as well once I get to it.

[cosmick]

Originally Posted by Andrewhans

I think the AWD is costing me a lot but I have no way to confirm it. I can't remove the front shafts because the transfer case has a viscous coupling with a 40/60 split to it. Without the front connected the transfer case would burn up within a mile or two. I have seriously thought about buying a used 4x4 transfer case, installing it and just making it stay in 2wd.

5.3 engine, 3.73 front and rear, 275/55/20 tires. The wheels are 20x9's which is a factory tire/wheel combo on newer GMC Sierra's.

You can safely drop to 255/60R20s, without them looking stretched.
Transfer case would help, but it would still be always spinning the front shafts and front diff / gears, plus a proper transfer case gives you low range, but has no differential. If you are going off road, the low range will help on descents, and stick with 275/55s.
If you can, do the transfer case and pull the front shafts, that should get you equal to a 2wd.
If you do the tc, go ahead and upgrade to a NP241C, with a new chain and new seals, plus new synthetic lube. Then you'll never have to give it another thought.
Your tires are taller than i assumed, so the 3.73s may be about ideal.

[cosmick]

Originally Posted by darcane

At 285hp for the 4.8L vs 295hp for the 5.3L, I was fine with the smaller engine. They are pretty close in performance, with a slight edge in power for the 5.3 and economy for the 4.8. In spite of the high gears, it tows our 4500+ lb travel trailer

The 3.23s are too tall for best mpg, but they do let you shift to a lower gear at higher speeds, which can help highway towing.
When it was new, and came with 3.42s standard, GM called the 4.8 " a real sweetheart " in regard to fuel efficiency, ( stock ). Back then the standard tires were 235/75R16, which was unusual. I drove a U-haul one and was impressed, it pulled away from a Vortec 5.7L C1500.
That's part of why i have bought 2 of those engines since. That, and they can be turbocharged past 1200 horses with just porting, a cam, valvesprings, ring gapping, injectors, fuel pump, and a tune. Doesn't even need forged pistons. I still have one, not turbo'ed yet.

[Andrewhans]

I'm hoping people claiming 23 and 25 mpg are talking about flat road cruising at highway speeds. If that is the case I already can hover around those numbers according to the DIC. This is very easy to do right now.

The reason I feel this goal is so difficult is I'm looking for a normal day to day tank average of 20mpg. Not a none stop highway trip either.

If people are actually getting tank averages of 21-23mpg... then I have a long way to go or some major changes that needs to be made.

Or maybe the route I need to take to work each day simply will not allow that to happen based on traffic lights on the highway I can't help but hitting.

Or the AWD really is that draining with this drivetrain.

[cosmick]

I was talking about a steady cruise. For a commuting average, you might manage it with an S-Blazer, but not a Tahoe.

[Andrewhans]

I figured most were.

My current record for a one way trip from work parking lot to my driveway is 19.1 going off the trip average on my Torque app. If I go off my DIC its upwards of 21mpg for the same trip. My DIC reads inaccurate for the tank average compared to hand calculating it, pretty common really.

For my day to day driving it's always the Torque app that I pay attention to. It's far most accurate and reads lowered which makes me pay more attention to how I'm driving.