2 weeks ago i took my first long trip with the civic hybrid (automatic transmission). i was driving from san jose,ca to los angeles the first day, and then on to san diego the second. LA is around 400 miles or so from san jose. i only got my car in march and with each tank of gas my mpg has increased steadily from around 42 to about 48 currently. i had just filled the tank the nite before i set off on my trip and cleared the trip odometer. when i started driving for about the first 1 1/2 hours or so i was pegged at 48.1 mpg. i was crusing about 70 miles per hour the whole time. then, my mpg slowly started to drop a little about every 5 minutes or so until i was at 45.7 mpg. Hwy 101 is fairly flat where i was at the time, which was south of salinas. i pulled over at a gas station thinking maybe i had a flat tire. but all was well. my "hot" tire pressure was in the high 30s. the rest of the trip progressed with the mpg staying at 45.7 and occasionaly hitting 46.1. the entire time i was in LA and san diego doing a "normal" type commute to a class i never went above 46.1 and ocassionally went down to 45.7. granted, 46 mpg is still good but i figured once i finished the long trip and wound up at my destination and got back to regular driving my mpg would go back up to where i thought it would be, around 48 or so. the next time i go to get gas i will reset my trip odometer which is what i normally do when i get gas. i didn't reset it the whole 1 week i was in southern cal since out of curiosity i wanted to see how many total miles i drove on the trip.
on my drive back up from LA to san jose i got 45.7 almost the entire way, going about 70mph.
does any of this seem strange? thanks for any information!

To me it seems pretty normal at 70mph.

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

Your mileage doesn't sound that bad. Were you using cruise control/air conditioning?

If you took I-5 and drove through the grapevine before Castaic Lake at 70MPH heading south, that would have caused a major MPG hit. If you took the windy roads of SR-101, I'm surprised your mileage wasn't worse.

If you stuck to 65MPH and increased your cold tire pressure to the high 30s, you would have probably been closer to 48-50mpg. But I know that Bay Area-L.A. drive pretty well. I drive it every few months. Its tough to stay at 65 with everyone else driving 80-90.

thanks for the replies! i wasn't using air conditioning or cruise control by the way. maybe the drop in mpg over the san jose to LA part wasn't strange then. but how about the fact that my mileage never went back up once i got to my destination and then settled in over the week taking regular commute style trips?

any difference in elevation?

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

I would expect that your mileage would have become worse once you got to your destination because you would have been doing more sidestreet/short distance trips vs. a long highway trip. That might explain the flat MPG once you arrived.

I notice that my tank average goes up to 50-52MPG during a 100-150 mile highway trip w/ minimal traffic, but once I get back home and drive locally (to work/errands/etc.) my mileage indicator "normalizes" and reverts back to 47-50MPG.

When I travel from Sacramento to the Bay Area on I-80 at 65mph, going a little up and down, surrounded by cars, trees, hills, etc., I get over 50mpg.

When I travel from Sacramento to LA on I-5, going 70mph, out in the barren open flat land, surrounded by nothing, I get around 45mpg.

I think your numbers are pretty reasonable. As has been mentioned, if you were able to go 65mph on that stretch of 101 (that's usually the speed limit), you'd probably get closer to 50mpg. That's why I personally prefer to take 101 rather than I-5 (not to mention the more pleasant scenery on 101).

i guess one thing i still find strange is that my mpg still has not strayed from 45.7. before i took my trip i was getting close to 48 mpg doing my regular everyday things. when i commute to work on the 280 towards palo alto i drive about 70mph for 20 minutes. if i wind up in stop and go it changes a little but not much. so i guess i'm just surprised that my mpg hasn't gone back up yet after the long trip. basically i'm getting the same mileage doing everyday commute things as i got doing a 6 hour 70 miles per hour trip, which is 45.7. whereas before i was steadily getting better and better mpg until i got to 48.

Did you fill up after the trip yet?

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

I guess I'll just ask the obvious. Have you reset your odometer?


Also, have you checked the pressure on your tires? A long trip like the one you've taken might have reduced your tire pressure a bit. As we all know, our cars are much more sensitive to tire pressure variations.