Quick update:

I am now getting 48mpg - much higher than 44-45 I've been averaging (and 46 I was working on) before my oil change - 160miles into 1st full tank after oil change. I am still not sure what happened to the 1/2 tank after oil change but everything is better now.

 

i just got my first oil change done yesterday. i immediately noticed a marked decrease in FE on the iMPG guage as well as on the MPG readout.

i usually average over 50 MPG quite easily...now i'm down to about 44. not quite sure who/what is to blame.

it was a dealer service. i suspect they put in 10w30? regardless, the mediocrity and idiocity of the southern california workforce comes under suspicion. even the service writer initally wrote the car up for a 26.99 oil change rather than the 39.99 for hybrids.

 

update: i've contacted the dealer with little success. apparently they don't make mistakes.

i've driven the car almost 200 miles with little resolution. i have noticed that at lower rpm/speeds the iMPG gauge is severely affected. whereas, at higher rpm's/speeds the fuel economy seems more inline with what the car was getting.
this leads me to believe that perhaps a more viscous oil would have a greater affect at lower speeds and perhaps the oil is not 0w20.

regardless, i just purchased mobil1 0w20, filter and a crush washer. i will redo the oil change myself.

 

Man you guys are scaring me about getting an oil change. I still have another 5000 miles though.

 

I've had my dealer change my oil in my 2006 HCH 3 times now. (I drive about 800 miles to work each week and now have around 21,000 miles on my odometer.) I have experienced a slight decrease in MPG's but it wasn't due to new oil. My dealer readjusts my tire pressure back to "factory specs" (around 35 PSI). I have to remember to pump them back up to 44 PSI (stock Dunlops).

 

OK, PROBLEM SOLVED!

i put my car on ramps, drained the oil, replaced the oil filter, plugged the oil pan, flushed a quart of 0w20, ran the engine for 20 seconds, redrained the flush oil until dripped dry. filled with mobil one 0w20, 3.4 quarts.

i just came back from a 20 mile round trip test drive and averaged 53.3 MPG at 62mph. the iMPG gauge dances like it used to and my mileage seems to agree. the car just feels right.

this was clearly the dealer putting in oil other than the manufacturer's recommended 0w20. i would love to get the drained oil analyzed just to neutralize the arrogance of my service writer at the dealership. what a jerk he was.

it is funny how we get to know the characteristics of our cars, i knew immediately that something was wrong when i was driving it home from the oil change. (9k plus miles of familiarity).

for the benefit of others...symptoms to look for:

the iMPG gauge doesn't move up as dynamically when letting off the gas.
notice that <35 mph driving (engine pulling) reads only 2-3 iMPG bars
yet at higher speeds you are able to max out the iMPG albeit with greater
difficulty.
200 plus miles of driving since oil change with no improvement of FE.

 

I'l bet it's the AC. Think about it. For most of you the last time you changed your oil was in the spring. Now it's summer and your AC is working harder to keep the inside of your car cool. Just my humble opinion. :-)

Kelly