got my first oil change and gas milage took a nose drive

[timcrow00]

i have a 2011, scsb with 4.8. i finally got my first oil change at 5000mi. before i was getting 17 or 18mpg. i havent filled my tank to check exact milage but can tell gas milage has dropped quite a bit, so has performance. the dealership put their oil in it and i drove it home and put mobile 1 in it the next day. any ideals what could be goin on?

[bighaas79]

For model year 11 and newer, I believe all gm vehicles use gm dexos oil for best mileage and emissions. If you look in your owners manual it will tell about it. Now it will also say that if dexos is not available that 5w30 can be used as a substitute. Does this affect milleage and what not? Couldn't say. I'm gonna say they switched to this oil just like ford came up with 5w20 a while back to be able to sneak their ratings for mileage and emissions up just high enuf to get past their required govt. ratings. I'm curious as to why you let the dealership change the oil if you turned around and put your own oil in it a day later? My guess is they would have used the dexos oil. stuff isn't cheap either. You probably just drained about $50 worth of oil out of your truck.

[jeffg1010]

its the government and the oil companies... they're feedin' us a bunch of lies man. haha!

That is interesting though, I will be anxious to hear what you figure out.

[timcrow00]

Originally Posted by bighaas79

For model year 11 and newer, I believe all gm vehicles use gm dexos oil for best mileage and emissions. If you look in your owners manual it will tell about it. Now it will also say that if dexos is not available that 5w30 can be used as a substitute. Does this affect milleage and what not? Couldn't say. I'm gonna say they switched to this oil just like ford came up with 5w20 a while back to be able to sneak their ratings for mileage and emissions up just high enuf to get past their required govt. ratings. I'm curious as to why you let the dealership change the oil if you turned around and put your own oil in it a day later? My guess is they would have used the dexos oil. stuff isn't cheap either. You probably just drained about $50 worth of oil out of your truck.

I let the dealer ship change the oil first because I have free oil changes but that doesn't include synthetic. If I want that I have to pay the difference but it's still cheaper to go buy it and do it myself. I change the oil twice in one day because the in the first 5000mi oil gets pretty dirty.
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[timcrow00]

Iknow about the dexos, and it says that mobile 1 is the only substitute that doesn't void the warranty per my dealership. I've always used mobile 1 and always felt vehicles run better with it so can't figure out whats goin on
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[piecesparts]

I am running Mobil 1 in my 2011 truck with a 5.3 and a set of 3.42 gears on the rear end. I run the highways around 75 MPH and get 19.5 to 20 MPG with it regularily. I now have 18,000 miles on the truck and have changed oil in it more than once. I have not had the dealer do my oil change, because I did not want to deal with the trip to their shop. I have my own lift.

[vin63]

Originally Posted by timcrow00

Iknow about the dexos, and it says that mobile 1 is the only substitute that doesn't void the warranty per my dealership. I've always used mobile 1 and always felt vehicles run better with it so can't figure out whats goin on
Posted via Mobile Device

If you feel the mileage drop is that significant, and there was no other change (driving habits included), I would take an oil sample and send it off for analysis.

[919cw313]

Originally Posted by timcrow00

...i havent filled my tank to check exact milage but can tell gas milage has dropped quite a bit, so has performance...

Exactly how can you tell?

[piecesparts]

Originally Posted by timcrow00

I let the dealer ship change the oil first because I have free oil changes but that doesn't include synthetic. If I want that I have to pay the difference but it's still cheaper to go buy it and do it myself. I change the oil twice in one day because the in the first 5000mi oil gets pretty dirty.
Posted via Mobile Device

I'm having a little complication understanding this statement. I am also trying to understand why the change at the dealership and then the change at home. The cost of an oil change at the dealership, (IF you want the Mobil 1) is more, but then again, you paid for the oil that you brought home to put in your truck. The cost of it (even at Walmart) is somewhat significant.

I would also support that with the thought in one'sw mind that the engine is getting broke-in, that the driving style will become more aggressive.

[timcrow00]

man i wish you guys could just answer a question instead of picking it apart! i try to keep things short and not write you guys a paragraph that takes forever to read. when i bought my truck it came with free oil changes(basic oil only, synthitic is about $30 extra). so at 5000 mi i took it in for the first oil change. after i got the truck home i checked the oil and it was already dirty. i guessing the guy who changed it didnt let it drain very long. so i went ahead and put mobile 1 in it and now the oil is nice and clean but my milage and performance is reduced. i know because i used to be able to drive to my hunting area and back on 1/4 of a tank but now it takes atleast 3/8 to do the same and i can also feel the power difference is reduced. i know this is not firm evidence of a change but i know my truck and im not stupid.

[piecesparts]

Originally Posted by timcrow00

man i wish you guys could just answer a question instead of picking it apart! i try to keep things short and not write you guys a paragraph that takes forever to read. when i bought my truck it came with free oil changes(basic oil only, synthitic is about $30 extra). so at 5000 mi i took it in for the first oil change. after i got the truck home i checked the oil and it was already dirty. i guessing the guy who changed it didnt let it drain very long. so i went ahead and put mobile 1 in it and now the oil is nice and clean but my milage and performance is reduced. i know because i used to be able to drive to my hunting area and back on 1/4 of a tank but now it takes atleast 3/8 to do the same and i can also feel the power difference is reduced. i know this is not firm evidence of a change but i know my truck and im not stupid.

Define dirty..... Oil will not stay absolutely clear unless it is a synthetic.

[gmclowsierra]

boy you guys are missing the point. does it really matter what oil hr did or didnt use. its not going to change the way the engine works that much. we run 10-30 oil in every gas engine and 15-40 in diesel trucks. it doesnt change the mileage that much if any. my question is did they do anything else. rotate the tires adjust the air pressure. anything like that?

[timcrow00]

thanks for getting to the point, i dont think they would of rotated the tires at 5000mi and i have checked my air pressure and no change there

[piecesparts]

Apparently the air in Mulvane got really thick just after your oil change. More wind resistance. Just to cap what we know or want to know

So to date:

oil change----twice @ 5000 miles (first them and then you) How many quarts did you put in???
MPG decreased significantly
no tire rotation (as far as you know---I would have just to keep the tires balanced)
tire pressures are all the same
performance on the engine has dropped off
Does the dealer know anything about an engine problem---have they put it on a computer to test
You are using the same fuel as before
Have you changed your driving habits in any way---driving more city than before etc...
Is oil pressure still good
no check engine lights
Does the engine run hot?
do all of the wheels rotate freely---no brakes hanging up etc...
Does the exhaust smell funny (cats working too hard or getting hot???)