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Old 08-02-2015, 09:57 PM   #1 (permalink)
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good mods for a new to me gmt 800?

I just had a family member sell me his old pickup truck cheap. its a 2001 Chevy Silverado with the 4.8 liter engine 4 by 4 Short Box regular cab.I'm going to end up selling my Kia Soul in the near future because I'm sick of paying for it and I only live 2 miles from work. I do like to visit state parks from time to time however and that's where a mpg bump might make a little difference. the truck runs well for the miles it has but I'm looking for some minor increases in fuel economy it gets like 17, and it only has an 18 gal tank, so its not that bad to fill. Anyone have any proven mods for the chassis? I learned how to drive for mileage in my gf's insight, so I have that side of it covered for the most part

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Old 08-03-2015, 07:32 AM   #2 (permalink)
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I own and have driven both GMT800 and 400 series 4x4s. Here is what has worked for me in the past. Assuming your truck has the 4L60e 4 speed automatic, the best mod would be to swap it out for a stick shift, such as the NV4500. I did this in my GMT400 and picked up huge mileage gains. GMT800 trucks were available from the factory with a stick so everything should bolt up, but you would have to have your computer swapped or reprogrammed. Obviously this is not cheap.

Second, pick correct tires, with tread pattern (not size) being the most important. Stick to high quality street tires for mostly street use, I have good luck with Michelin LTX M/S2 on several 4x4 trucks. If you need an all terrain, stick to a mild all terrain, don't put aggressive mudders on a street truck they handle terribly onroad. Try to stay at stock width or less, taller is ok since you get better "rubber gearing" out of them, just remember to adjust your odometer/speedometer to compensate.

From there, make sure your truck still has the appropriate factory air dam up front since this is cheap and easy to fix. A aeroshell or some sort of bedcover would be great for aerodynamics. If you want to go hog wild swap the fleetside bed for a stepside bed and then build a custom aeroshell on that. If not a flat bedcover will help some, keep a lookout on CL for a used one cheap.

I would swap all the long term gear fluids in the truck out for a name brand synthetic, front diff, rear diff, transfer case, and transmission. You might pick up a bit of MPG, but it is just a good idea when getting a new to you vehicle to ensure you have proper lubrication.

Make sure your front radiator is not blocked or full of gunk and clean it out/replace it if it is. Your 4l60e will not like inadequate cooling and it is possible to have it constantly running hot (but not hot enough to throw a code) due to inadequate radiator airflow. Been there, done that (why I had to swap to a manual).
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Old 08-03-2015, 08:04 AM   #3 (permalink)
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I hope you're riding a bike those two miles and not driving a vehicle. Horrible death to the vehicle because of the twice-daily, short run.
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Old 08-04-2015, 04:39 PM   #4 (permalink)
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I'll add a few additional mods to the list that aardvarcus proposed.

1. Assuming that you have steel wheels, switch to stock aluminum wheels of the same size. Craigslist in my area is full of takeoffs that can be had fairly cheap. I did this with my 2007 Silverado Classic and dropped 7 pounds of unsprung weight off of each wheel.

2. In later years (I think starting in 2006) electrical cooling fans replaced engine driven fans in the Silverado lineup. Swapping your clutch and fan assembly for an electric fan would give you another little boost in MPG.

3. Aluminum drive shafts were used in some configurations of the GMT800 chassis. If yours is steel, swapping it out should remove roughly 25 pounds of rotating mass from your drive line.

Used parts are available for all of these things, and obviously they work as GM included the features in later GMT800 models of the Silverado.



Lastly, I'm a really big proponent of using a Scangauge to learn how your vehicle responds to various driving styles and mods. The biggest single thing that I ever did to improve my mileage, was to learn to stay out of the throttle in my Silverado.

Enjoy your truck!
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Old 08-11-2015, 04:42 PM   #5 (permalink)
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I know it has stock alloy rims, so not much I can do there. The tires are some Goodyear silent armor somethings and are good all around tires

I will have to look into the driveshaft, but with short box short cab the difference may not be as dramatic,
I will have to look into the fan too

Did the suburbans come with an air dam? Mine is a z71, so there was no air dam from the factory. Did they make a good difference?

I've kept it maintained well over the years for him, so the truck isn't exactly new to me,

And I know that driving the short distance is hard on it, but it can't be helped. There is 200ft of elevation change and two really busy roads to contend with. I'd rather cause a slow death to my vehicles than a fast one for me
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Old 08-11-2015, 05:05 PM   #6 (permalink)
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I'm not sure about the Silverado or Suburban air dam, but an effective air dam would help with mileage at highway speeds. You should be able to fashion one from plastic lawn edging material. There are several examples of those on ecomodder.com
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Old 08-11-2015, 06:35 PM   #7 (permalink)
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Quote:
Originally Posted by hansj3 View Post
I know it has stock alloy rims, so not much I can do there. The tires are some Goodyear silent armor somethings and are good all around tires

I will have to look into the driveshaft, but with short box short cab the difference may not be as dramatic,
I will have to look into the fan too

Did the suburbans come with an air dam? Mine is a z71, so there was no air dam from the factory. Did they make a good difference?

I've kept it maintained well over the years for him, so the truck isn't exactly new to me,

And I know that driving the short distance is hard on it, but it can't be helped. There is 200ft of elevation change and two really busy roads to contend with. I'd rather cause a slow death to my vehicles than a fast one for me
In '03, the Silverado changed it's front sheetmetal, but the Tahoe and Suburban retained it for a few more years. I'd look for a lower bumper fascia and air dam off an '05-'06 Tahoe or 'Burb since those had the largest air dam. '05-'06 also had the e-fans. Those two mods were supposed to be about a 1mpg bump over the '04 model. Note that the fans aren't quite plug-n-play. You need a tuner to modify your CPU to switch the fans on and off and a wiring harness (I had planned to use http://www.blackbearperformance.com/services.asp).

That 4.8L is a great motor, I've got one in my wife's 2wd Tahoe that we can get 25mpg hwy with, and I had one in my old Silverado. You may get some ideas from the thread in my signature for the Silverado.
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Old 08-12-2015, 02:56 PM   #8 (permalink)
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Quote:
Originally Posted by darcane View Post
In '03, the Silverado changed it's front sheetmetal, but the Tahoe and Suburban retained it for a few more years. I'd look for a lower bumper fascia and air dam off an '05-'06 Tahoe or 'Burb since those had the largest air dam. '05-'06 also had the e-fans. Those two mods were supposed to be about a 1mpg bump over the '04 model. Note that the fans aren't quite plug-n-play. You need a tuner to modify your CPU to switch the fans on and off and a wiring harness (I had planned to use Black Bear Performance :: Custom Tuning Solutions for 96 and newer GM Vehicles).

That 4.8L is a great motor, I've got one in my wife's 2wd Tahoe that we can get 25mpg hwy with, and I had one in my old Silverado. You may get some ideas from the thread in my signature for the Silverado.
I read through the post in your signature and I was just wondering how much improvements did the behind the grill block give you vs the in front grill block?
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Old 08-12-2015, 04:16 PM   #9 (permalink)
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Originally Posted by hansj3 View Post
I read through the post in your signature and I was just wondering how much improvements did the behind the grill block give you vs the in front grill block?
What was most telling was how quickly the engine warmed up in the winter months. There was a significant jump when I moved it to the front, which indicates to me that I was getting a lot of air flow going past it when it was mounted behind.

I didn't do any A-B-A testing, but looking at average mpg before and after, it was somewhere around 0.5-1mpg by having it in front and little to no gain by having it behind.

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