Fuel economy getting worse

[jambo101]

Started the big trip to Fla and after the first days driving my Scanguage read average fuel economy for the day as 42.5mpg..great
Second day of driving and that 42.5mpg reading slowly dropped to 35.4mpg:eek::confused:

Only thing that changed that i could see was the outside air temperature which went from 25 degrees on day 1 to 80 degrees at the end of day 2.Only possible theory for the poor fuel economy i could think of was poorer rolling resistance of the winter tires as the weather got warmer.
Any one have any other ideas?
Guess i'll have to break out the old pencil and paper system on the way back just to make sure this electronic gizmo is working correctly.

My other electronic problem was with the Garmin Nuvi 255 GPS unit which inexplicably wont turn on any more:iono:
I've had it for about a year and a half and its worked well on the half dozen times i've used it.It worked for 15 hours on day 1 of the trip but wont turn on on day
2 of the trip :iono:
Any ideas to get it working again?
Thanks..

[R2D2]

Is your cig lighter socket working, jambo? If the fuse popped and ran down your GPS batt it may be why it won't turn on. If it's ok plug in the GPS and wiggle the power cord to see if there's a break causing an intermittent condition.

As for your FE, see how it calculates at the pump. That's a big drop when if anything I would expect an increase due to warmer weather. Was there a headwind for the second tank that may have gone unnoticed or more AC use? Big terrain change? It seems there would have to be multiple factors contributing to a drop that big.

[jambo101]

Took the gps unit to Bestbuys where the geek squad diagnosed defective power cord, $13 later with new power cord unit works fine.
The low mileage problem is a head scratcher as last summer i got as high as 49.9mpg while crossing the prairies. wonder if the scanguage unit is defective or has had a parameter adjustment.but on the first leg of the trip it acted normal and i watched the gauge climb slowly for 15 hours, then on the second 15 hours its like it was going slowly backwards:iono:

[Lil Abner]

I took off my snow tires over the weekend, and put my summer tires back on, and my mileage instantly went up. On a day that it's above 40-degrees ambient temp, I'm back to my 50mpg. But when it's around freezing, it drops down to low 40's. With my snows, I was lucky to touch 40 mpg. So the cold temps and snow tires is probably what's killing it.

[Yaristeve]

...i watched the gauge climb slowly for 15 hours, then on the second 15 hours its like it was going slowly backwards:iono:

What goes up must come down...

Since nothing is perfectly flat, maybe you're on a slight downgrade the first half and a slight upgrade on the second half?

[TLyttle]

"Nothing is perfectly flat", but until one has driven the Prairies, that is questionable. Saskatchewan is where one can spend 3 days watching their dog run away. I think it is a slope of 900' over 1200 miles...

The only variance out there is wind: headwind going west, tailwind going east. Otherwise, see paragraph one!

[the_boss]

i can do max 350kms on the highway at 110km/h, when im in town, i can reach 550kms. When the weather is warmer, i can do more mileage with the car. I drive 1200kms each week end since 13 months and i can confirm that the temperature have a LOT to play with mpg!

[Cosworth]

It's gotta be your snow tires. Most snow tires are designed for temperature range up to ~45degC. After that point, your tires are just like soft rubber. You should check and see if you have any tread left after the trip in the warm weather. I can't imagine there's must left of the winter rubber compound.

I don't drive w/ my snow tires when temp approaches ~40degC.

[JDfan33]

I'd put my money on the snow tires too... do you run both sets of tires at the same psi?

[jambo101]

My brother brought up an interesting point as i told him my best mileage for the trip was from Montreal to NYC which was done entirely on fuel purchased in Montreal,for the rest of the trip i've been subjected to fuel containing at least 10% ethanol, i'm wondering if that plus the ties and the newly added 10w-40 oil arent all conspiring to give me crappy mileage..if so its amazing that such small changes from my last trip with summer tires and mostly done in Canada could reduce my mpg to 30 from 45:eek:
I may redo the oil change to 5w-20 for the return trip..

[jambo101]

Problem solved, seems my Scangauge needed to be reset,just did a run up Floridas west coast at 45.1mpg:biggrin: