Sudden Mpg Loss

[adamstokes88]

I have an 04' Sierra 2500 6.0 with 72000 miles, recently I have lost some mpg's, I live around

Atlanta, GA and the lowest it has gotten is 15F. Is cold weather to blame, I don't let the

Truck warm up unless there is ice on my windows, and that has not happened this tank of gas

I track my mileage to make sure nothing is wrong with the truck, so if not the cold weather,

Should I stary by replacing the PCV valve? Thanks for any and all suggestions.

[txab]

Could be something as simple as tank of low quality fuel. It can happen even if you fill it up a the same place all the time. You might keep tracking it. I think the 6.0 has a fixed orifice in place of a PCV, the 5.3 does. No need to replace it

 

I'd check the air filter. You might clean the MAF with MAF cleaner if you haven't done so in a while.

 

Have you owned this truck for a while? It's never had this problem during winter before?

 

What type and weight of oil are you running? Synthetic or dino?

[adamstokes88]

Yea I fill up at the same place all the time. I bought the truck in April 2009 with 55,000 so this is my first winter with it. I'll try cleaning the MAF sensor and air filter. I use Mobil One 5w30 full synthetic oil. Thanks for your help.

Anything else I can check on?

[GPGuy]

I'd say the colder weather is to blame, combined with "glorious" winter gas. You could have just gotten a bad tank of gas as mentioned. I'd monitor it over the next few tanks before you start changing anything. It wouldn't hurt to check the air filter though.

[txab]

Yea I fill up at the same place all the time. I bought the truck in April 2009 with 55,000 so this is my first winter with it. I'll try cleaning the MAF sensor and air filter. I use Mobil One 5w30 full synthetic oil. Thanks for your help.

Anything else I can check on?

 

If it suddenly dropped it points more towards a possible fuel issue. As stated above, winter blends make a difference. The location where you purchase may have gottem a load of fuel from a different location. If you suspect a quality problem you might try another brand. If you have a choice, you might want to avoid the "10%" ethanol fuel. I do whenever possible

[xaugievike]

My 6.0l HATES the winter temps (different climate than yours).....I keep track and I have routinely seen 2mpg drops when the temps fall up here....

[davzog]

I agree with the winter fuel blend being an issue....I let mine idle a little to warm up before I drive off...not a lot but it accumulates for a mpg loss....

 

It takes longer for the truck to warm up in the winter....mine won't shift into overdrive until I get about 4-6 miles from home, driving 45-55 mph at 2300 rpms is not good for fuel mileage

 

I generally get in the low 14's over summer and am currently running about 12.3 mpg or so.....dammmmm cold.

[Rat4go]

I'd bet it's the cold. Engine takes longer to get to temp so it uses more fuel in the process as more of the fuel's energy is used to heat the coolant. Also, cold weather also makes axle lube and bearing grease more viscous, increasing friction. Synth products help a little, but.....

 

I used to have a 2001 6L 2500 with the 4-speed. When it got cold (below about 40f) outside, the trans never got warm and the fuel econ got quite a bit worse. These trucks have a pretty big aux trans cooler on it that's really only needed when it's warm out or when towing. In the winter time, I covered the front of trans cooler with a piece of alum sheet (flashing) using big zip-ties to hold it on and the trans ran at more 'normal' temps (150f or so instead of 100f) and fuel econ got noticably better (almost 2mpg). The trans still has the cooler in the radiator tank, so it's not like it's not being cooled....just not being cooled as much as having freezing air blowing over the aux cooler! Pretty simple to pop off the close-out above the grill to access the cooler to cover it.

[adamstokes88]

Sorry for the late response, I cleaned my MAF sensor and filter off and I plan on running it through a tank or two and see if there's any change. I'm almost certain it's the cold though as everyone has posted, thanks for all the suggestions and ideas.

[Kodiak450]

I get crappy mileage with certain gas at times, but noticed sunoco's 89 and exxon's 89, tend to give me slightly better mileage. I never use 87 nor would recommend it regardless what GM says. Run 89 or higher, after a 2-3 fill up's, you'll notice a little better power all around.

[ColoradoSkiCountry]

If I run 87 or 91 Octane up here at 5280 feet, the engines tend to ping. It's 85 that works best up here.

[Kodiak450]

You shouldn't be hearing any pinging with higher octane, if anything the lower octane would do it. GM uses a really good knock sensor control, so good that most people opt to use lower octane fuel. I also noticed that my 6.0 runs better on synthetic oil vs conventional, not sure if the SYN will give mileage a slight edge, but since switching to SYN, my engine feels like it has better performance all around. Feels quicker too , once the light turns green.

 

Also during winter, there is different additives for the fuel as oppose to warmer season. I think during colder temps, engines like to run better. Especially with this frigid artic air that has been over the area here for the last few weeks.

[deerchooper]

I also noticed that my 6.0 runs better on synthetic oil vs conventional, not sure if the SYN will give mileage a slight edge, but since switching to SYN, my engine feels like it has better performance all around.

 

 

i think different on this one. i dont know what type of oil was in the truck when i got it used but it did have an ac filter on it. but i switched from ??? to mobil1. i drive 700 miles or more a week. on my 156 mile round trip i would use 3/8 of a tank, or 3 days of driving. now im using more or close to 1/2 a tank or filling up every 2 days. i did this oil change about 4000 miles ago around turkey weekend. and i havent see it get better. i dont know if its some voodo thing, winter gas or the oil change. it very well might be all 3 as it did change when i did the oil. same roads, same cruse set and same load. i also changed the rear diff to mobil1 that weekend.

 

 

maybe its me, but my wallet isnt lying.

[Kodiak450]

I also noticed that my 6.0 runs better on synthetic oil vs conventional, not sure if the SYN will give mileage a slight edge, but since switching to SYN, my engine feels like it has better performance all around.

 

 

i think different on this one. i dont know what type of oil was in the truck when i got it used but it did have an ac filter on it. but i switched from ??? to mobil1. i drive 700 miles or more a week. on my 156 mile round trip i would use 3/8 of a tank, or 3 days of driving. now im using more or close to 1/2 a tank or filling up every 2 days. i did this oil change about 4000 miles ago around turkey weekend. and i havent see it get better. i dont know if its some voodo thing, winter gas or the oil change. it very well might be all 3 as it did change when i did the oil. same roads, same cruse set and same load. i also changed the rear diff to mobil1 that weekend.

 

 

maybe its me, but my wallet isnt lying.

 

 

How about your tire pressure? Check it lately? I noticed mine dropped a bit when the really cold temps came and had to add more. It dropped abour 10-15 psi from the normal setting. I generally think that the better mileage is sought out in colder temps. Engine doesn't have to work as hard keeping cool, but not by much at all with better mileage. Maybe 1-2 tops.

[deerchooper]

How about your tire pressure? Check it lately? I noticed mine dropped a bit when the really cold temps came and had to add more. It dropped abour 10-15 psi from the normal setting. I generally think that the better mileage is sought out in colder temps. Engine doesn't have to work as hard keeping cool, but not by much at all with better mileage. Maybe 1-2 tops.

 

checked and adjusted. had the tpms every morning for a couple miles, fixed the air pressure 3 days into that.