Help with Yukon gas milage

I have a 2001 Yukon. From the day I bought it until November '05, it got 18 mpg. I was pretty happy with that, and it did so city or highway. The worst I ever got (without my trailer) was 17.5 and the best was 18.8.

Suddenly...I mean really suddenly, in November I started getting 15mpg. Since Nov. it has ranged from 14.9 to 15.6.


The 60,000 mile service was due, so I told the dealer about it. They did everything they could think of: changed oil and fuel filters, tranny service, front and rear differential service, air filter, cleaned the injectors, rotated tires and checked inflation, and more.

I got it home, filled it, drove the tank down and filled it again. 15.2mpg
:mecry:

Anyone have any ideas besides what I've tried? The only other suggestion is that that state switched to the "winter recipe" gas with ethanol in November, but I can't verify that.

Thanks!

Did you change the spark plugs? Have you had the brakes checked? It's possible that one could be sticking a little, causing lots of extra drag. I gained 3hp on the dyno with my '04 Tahoe when I switched to Amsoil synthetic oil in the differentials and transfer case. I don't know exactly how much my MPG increased, but it had to have gone up some. I'd kill for 18mpg, I only get about 12-13...but that's probably because I have a supercharged 6.0L and a lead foot. :naughty:

Barring some mechanical problem that was missed by the mechanics, I would say it probably is a different gas mixture. I've been reading in the paper reciently that more and more gas stations are selling mixed gas and a product called E85 which is something like 12% gasoline and the rest ethanol. The majority of the gas stations that are doing this are in the Midwestern to Western US, so it is possible that the stations in Washington are taking part in the experiment.

Same thing happens to me during winter driving. My milage drops about 2 to 3 mpg starting in October or November-on short trips especially. I think it has to do with a combination of factors. Winter fuel blend, longer warm up time with auto choke on, thicker oil with the cold, tires very cold and greater resistance to easy rolling, slower driving(under 55 much more)and probably numerous other winter related reasons. Just my opinion.

bexteck said:

Barring some mechanical problem that was missed by the mechanics, I would say it probably is a different gas mixture. I've been reading in the paper reciently that more and more gas stations are selling mixed gas and a product called E85 which is something like 12% gasoline and the rest ethanol. The majority of the gas stations that are doing this are in the Midwestern to Western US, so it is possible that the stations in Washington are taking part in the experiment.

Click to expand...

E85 is well labeled as such, and only comes from a special pump because it will not work in the majority of vehicles on the road today. If the OP was using it, he would know about it.

Thanks for the suggestions folks.

My boss threw out another one: catalytic converter. As soon as he mentioned it I recalled smelling "hot" when I pull in the garage sometimes. I'll have to climb under and take a whiff to see if that's the source.

They did change the plugs, and I think (have to check the receipt) maybe wires too.

Another coincidence (?) was I had the brakes done last fall...maybe it WAS coincident with the drop in milage.

I can see your fine suggestions will keep me busy Saturday!

I would jump all over winter blend as being the problem but!

My Dad has reported better mileage for his last three tanks. And I can hardly believe he changed his driving habits THAT much!

I have been getting slightly less mileage with my Ram 2500 Cummins and I suspect winter blend.

I plan to try acetone on a 500+ mile epic tomorrow...

I hope to report good news!

its winter fuel.all my cars/trucks suffer from it.
i had to rejet a step richer in a 70 elcamino due to the winter gas.it was leaning out and pinging.
so its not your truck.
i can see it with the scantool on a van i use daily.change in long term trim that coincides with the formula change.