# fuel mileage dropped



## Detroitdan (Aug 15, 2005)

Wife tells me her fuel mileage is down, I drove it and noticed the same thing lately. I recently changed the oil and I checked the air filter, looked fine but I blew it out anyway. I'm thinking maybe we're starting to get the E-85 blend fuel that I heard about a few months back. No signs on the pump, but that stuff is supposed to kill gas mileage. Only other thing I can think of is the fuel filter, it hasn't been changed yet but I don't see how it could hurt, not like an old low pressure carb system, these have high pressure fuel pumps, would probably start running poorly if filter was plugged wouldn't it? It's an 04 Chevy Avalanche 1500 with a 5.3 and 36000 miles.


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## bryanj23 (Nov 17, 2006)

Detroitdan;342238 said:


> Wife tells me her fuel mileage is down, I drove it and noticed the same thing lately. I recently changed the oil and I checked the air filter, looked fine but I blew it out anyway. I'm thinking maybe we're starting to get the E-85 blend fuel that I heard about a few months back. No signs on the pump, but that stuff is supposed to kill gas mileage. Only other thing I can think of is the fuel filter, it hasn't been changed yet but I don't see how it could hurt, not like an old low pressure carb system, these have high pressure fuel pumps, would probably start running poorly if filter was plugged wouldn't it? It's an 04 Chevy Avalanche 1500 with a 5.3 and 36000 miles.


E-85 is from a seperate pump because not all vehicles can run on it, it HAS to be posted. Could it be because it is winter and she is warming up the vehicle? I know it is a dumb question, but I had to ask. I'm not a mechanic and when it comes to car engines I'm an idiot so that's all the farther I can go with this.


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## SnoFarmer (Oct 15, 2004)

What weight of oil did you use?

A heaver motor oil will cut into your millage.


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## Northland (Oct 1, 2006)

NOt only what weight did you use but did you switch from synthetic to regular oil. I brought my p/u in for a recall once and they had to drain the oil and change a part. Well...instead of putting Mobil 1 in like I had...the dealer pt pennzoil in. I noticed it as soon as I left the lot. I thought they flashed the computer and changed something. Well my mileage dropped 3mpg.. After a few days I thought about it and I called and asked them what kind of oil they used... Reserviced it and right back up to my old mileage.


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## Detroitdan (Aug 15, 2005)

No, I stayed at 5w30, there is no winter recommendation for these engines anymore, not like the old days. And the oil change had nothing to do with it, I just mentioned that because that was when I checked the air filter. She said it had been noticeable for a little while. And as far as 3 mpg drop from synthetic oil, no offense but I just don't believe that. I've tried synthetic oils before, I worked for AC Delco and for a Pennzoil affiliate so I know just a tad about oil, and I know that's BS. Oil has absolutely nothing to do with fuel efficiency. Unless it is low or wasted and the engine begins to fail, or if you run some ridiulously heavy oil, then you may see a little trouble but probably only when cold anyway, which is about 3 minutes. I got nearly 300,000 out of a 6.0 Chevy using the cheapest recycled 10w40 on the parts store shelf. And that's also with irregular oil changes, had 19,000 miles on the oil when I got the truck. The guy before me was using 15w40 in the winter because he thought that was winter oil. Didn't hurt it but it wasn't right. And, that truck was beaten like a rented mule every day of it's life. That being said, I do agree that synthetic is slightly better, but since conventional oil is more than good enough, the synthetic is just a waste of money spent on peace of mind. But if you believe it, good for you, I hope you are happy with your extra 3 mpgs.


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## SnoFarmer (Oct 15, 2004)

Use the Recommended Grade of Motor Oil 
You can improve your gas mileage by 1-2 percent by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1-2 percent. Using 5W-30 in an engine designed for 5W-20 can lower your gas mileage by 1-1.5 percent. 


Have you checked the psi in the tires, now that it is cold outside?


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## Detroitdan (Aug 15, 2005)

See, I've always said SnoFarmer is smart. 1 or 2% does not 3 mpg make. I am a believer in using what the factory recommends. These guys designing the engines did not go to school for engineering without learning something more than Joe Jiffylube. I have used QS 5w30 since it was new, and I change it based on the oil change interval timer, which works out to about 4-5000 miles. 3000 mile intervals is way too often, conventional oil doesnt break down until 6000 miles. On my old truck I change it every 5000 on the 5000s (150k, 155k, etc) makes it easy to remember. The 3000 mile interval was pushed hard by the quick oil change shops in the late eighties to sell more oil. Not because you need to. Look at Europe, they do their service on the metric equivalent of 6000 miles. Think of how much oil we could save every year as a country of Jiffy Lube and all those other guys weren't out to make the biggest profit they can by lying to you.

Where am I? Oh yeah, tire pressure. An excellent point. I actually just took the summer wheels and tires off a couple weeks ago, they are 305/45/22s, one would think the stock tires and wheels would be better if anything. I checked the pressure on the stock tires, they were all at 32 cold, door tag recommends 30 cold. Was thinking about raising it a little to make them harder and taller, but they have been wearing well so I think I will leave them alone. 

Other than that, don't know what it could be. No SES lights or anything, no rough running, no excessive idling. I'm the one warming my truck up for 15 minutes everyday. I bought her a remote starter so she wouldn't beat on it with cold starts, but who knows how long she really lets it warm up. I just got a remote starter on mine which is good because I won't drive it until it's warm, so I'm in the habit of firing it up then getting sidetracked and leaving it running for 30-45 minutes. Now it can only run 15, so I'm probably saving money!

I thought the E-85 was supposed to be getting added as a blend a little at a time, not straight whatever it is, I didn't mean we were getting pure E-85. I read about someone using a 15% blend on a new Tahoe and losing 4 mpg.


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## ThisIsMe (Oct 31, 2006)

Dan,
Pretty sure NH does not have the mix yet. Down here in MA we have it and it is causing havoc in anything but newer cars (read closed fuel system). It is a 10% blend that most states are going to. 

Seems it likes to suck up moisture and the moisture is dispersed in the fuel. I have been getting fuel in NH for gear besides the vehicle and up to last week did not see the sticker stating such on the pumps yet.

Boat dealer says they have had some many issues with the new 10% mix that they are putting water separators in the boats they sell now. I had to get one in mine. Heard from a few other people as well, let the fuel sit for a few and it soaks up the moisture, thus needing to dump the fuel.

I wonder of all the people dumping the old / bad fuel from chainsaws or such on the ground was ever figured into the reasonings for this new fuel?


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## Detroitdan (Aug 15, 2005)

I heard that a lot of cars, VWs in particular, are having a hard time with the fuel, destroying o-rings and gaskets and so-forth, and eating tank lining then sending it through the system. It's always something, isn't it?


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## ThisIsMe (Oct 31, 2006)

Detroitdan;342323 said:


> I heard that a lot of cars, VWs in particular, are having a hard time with the fuel, destroying o-rings and gaskets and so-forth, and eating tank lining then sending it through the system. It's always something, isn't it?


True. We need to start importing cars from Brazil now.

Was Brazil not a third world country a few decades back? Now they are down there running their cars off of corn at like 78 cents a gallon.

We really have come far here in the US


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## mayhem (Aug 25, 2006)

Detroitdan;342305 said:


> Where am I? Oh yeah, tire pressure. An excellent point. I actually just took the summer wheels and tires off a couple weeks ago, they are 305/45/22s, one would think the stock tires and wheels would be better if anything. I checked the pressure on the stock tires, they were all at 32 cold, door tag recommends 30 cold. Was thinking about raising it a little to make them harder and taller, but they have been wearing well so I think I will leave them alone.
> 
> Other than that, don't know what it could be. No SES lights or anything, no rough running, no excessive idling. I'm the one warming my truck up for 15 minutes everyday. I bought her a remote starter so she wouldn't beat on it with cold starts, but who knows how long she really lets it warm up. I just got a remote starter on mine which is good because I won't drive it until it's warm, so I'm in the habit of firing it up then getting sidetracked and leaving it running for 30-45 minutes. Now it can only run 15, so I'm probably saving money!
> .


Well the warm ups are just wasting gas, so thats not helping your fuel economy. Not sure how much fuel is conumed while idling a 5.3 for 10 minutes, but wased fuel is wasted fuel. I have a remote starter but it only gets used when we have a heavy frost, snow or if its single digits or below in the morning...other times I just start it and drive gently.

What about the OD difference between the summer and winter tires throwing the odometer off? Did you adjust the computer for the replacement tires and then back for the stockers?

As regards oil making a difference in fuel economy, my 2002 Altima gained about 2mpg when I switched from 5w-30 dino oil to 5w-30 Mobil1...2000 Silverado ecsb with the 6.0 I picked up roughly 1mpg, which percentagewise is inline with the gains in the Altima. On top of that I pushed my change intervals up from 5000 to 10000 miles with a filter change at 5000. I totally agree that any decent motor oil will do a good job of protecting an engine over a long lifetime and that switching to synthetic because its "better for your engine" is a point of diminishing returns is specious logic at best, but if you reduce the friction between mechanical parts then you will reduce the amount of energy it takes to make them move.


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## Joe D (Oct 2, 2005)

Most winter milage drops have to do with idle time and just running the defroster.
You didn't post how much milage you have dropped if so I missed it but how much we talking? Are you going by the milage display or going old school and doing the math?
As far as synthetic oils, I never noticed a differenc in using them as far as milage is concerned. It does offer better engine protection, heat breakdown, sludge, and deposits. I like that it flows better when cold and allows longer drain times. I keep my vehicles for the long haul so synthetic is a good choice for me but for someone who trades in all the time and never sees the high milage the only benifit will be the extended drain.


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## Dogbonz (Aug 11, 2005)

Gas pumps in Michigan have had the octane rating stickers in yellow on each pump for years,, and most if not all of the stations, have had 10% ethanol blend for years now. At 10% there are no adverse affects on drivability or mileage. They just put up a new Ethanol plant bout 3 miles from me,,, all the farmers are happy! If we could switch 50% of the cars on the road to E85 (85%Ethanol and 15% 115 Octane gas mix) We could tell all of the arab world to blow on the big one!!!!! And by cuttin the use of pure gas,, oil supplys would in crease and fuel prices would Decrease,,, Same with Bio Diesel.

E85 does not have the same BTU properties as Gasoline,, there for you will have a 10 to 15% decrease in fuel economy. But if we could do it for .75 a gallon,, who would really care?

As to your post,, Change the fuel filter,, check tires,, adn wifes driving style (lol) then if no change take it to dealer and have them trouble check the ecm. Maybe you have a Oxcy sensor going bad. I would dare say that you do have some sort of sensor going bad, and its telling you ecm to go to a rich mode. Good Luck


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## Detroitdan (Aug 15, 2005)

The summer tires are the closest possible size to the stock tires diameter, I researched it and found that any difference would be negligible to both speed and ecm calibration. I was told that if I went with the 295/45s I would have to have the ecm fixed, but with 305/40s at most my speedo might be off by a hair at highway speed. So it could be different enough to change the mileage, but if there is actually a noticeable difference between the two sizes, how come we didn't get more mileage when we put the 22s on last spring? 
She has been checking the mileage on the DIC computer, which I know isn't as accurate as doing the math, but it should be consistent. She claims she has gotten an average of 18 since she got it, now its only averaging 14-15. I'm going to throw a fuel filter in it just for fun, but I'm starting to suspect the fuel itself, I think the methanol is creeping into the area. I suspect they are allowed to blend a certain percentage before they advertise it. I already had the ecm reflashed once, went back to the dealer over the summer because it was lacking power and they said it had to be done. I have used QS 5w30 since new, so regardless there has been no change there.
As for her driving habits, you try to tell her that. I won't, I'm scared of her. I'm just glad she finally stopped wrecking cars and getting pulled over a few years ago.


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## Joe D (Oct 2, 2005)

Jack up each wheel and give it a spin just to see if any drag is there. Do you know anyone with a GPS? They display speed on them just to check your speedo. Has the DIC been reset?


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## Dogbonz (Aug 11, 2005)

> you try to tell her that. I won't, I'm scared of her I'm just glad she finally stopped wrecking cars and getting pulled over a few years ago.


 thats sad!
Funny but Sad


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## Sydenstricker Landscaping (Dec 17, 2006)

I do hope that everyone realizes that the quality of gasoline in the winter is less par than summer fuels. It has some kind of additive or something to keep it from freezing or going bad due to the low temps. Every year both my car and truck get worse mileage than the summer. Even my grandfather's saturn gets worse in the winter and he gets lik 35-37 mpg in the summer. That is just some food for thought.


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## Detroitdan (Aug 15, 2005)

next time I get to use it I'm going to measure it the old fashioned way.


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## Joe D (Oct 2, 2005)

Detroitdan;343246 said:


> next time I get to use it I'm going to measure it the old fashioned way.


Will she let you use it for a full tank?


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## timm9 (Dec 19, 2001)

I'm far from a mechanic but I did (stay in a holiday in last night? just kidding) experience a big drop in gas milage on one of my trucks with very low miles. My gas milage dropped 4 to 5 miles per gallon. It turned out that the oxygen sensor/optical eye was dirty and after cleaning it with a spray electrical cleaner the gas milage jumped back up to what it had been. Just my .02 worth.


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## Detroitdan (Aug 15, 2005)

good one, thanks for the input. I'll have to look into that.


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## timm9 (Dec 19, 2001)

I would love to sit back and look "smart", but the credit goes to my father in law. He had just read about it in a magazine.


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## REAPER (Nov 23, 2004)

Cleaning the O2 sensor is a good way to make sure it is working and should be done in routine maintenance if you own your own garage.

No one mentioned it so i will.

Change your spark plugs and cap and rotor 1st and if you have not done so yet I would replace the plug wires as well.


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## NorthernILPlwr (Oct 20, 2006)

REAPER;344463 said:


> Change your spark plugs and cap and rotor 1st and if you have not done so yet I would replace the plug wires as well.


actually the tune up on these trucks isnt due until 100,000 miles.....and there is no distributor cap and rotor.....its a DIS (distributorless ignition system). That being said you should not be having problems with tune up parts for a while.

Driving habits can play a part in fuel mileage. In addition to letting it warm up..... Maybe consider getting a K&N Filter or even a full intake kit. You can pick up as much as 3-6 mpg just by installing them.

As far as the O2 sensor is concerned, if you are going to remove it to "clean" it you may as well just replace it. Keep in mind on these newer vehicles the computer usually can sense the slightest of problems with vehicle sensors. They even keep track of misfires from the ignition system. If there was a problem that even you did not notice the computer will. Check to make sure the Service Engine Soon light is working. Just turn the key to Run without starting it and the light will illuminate for a few seconds.

just my .02

-NIP


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