In Southern California with all the fuel additives my '05 HCH averages about 41 mpg, 38 with AC on.

Just recently I saw a 25% drop in mileage overnight (30 mpg). For a hybrid, this kind of mileage in lousy and unacceptable.

I do all my own maintenance and keep the car in top shape. I just ran an OBD II scan and all systems are well within acceptable parameters, no error codes.

I suspected bad or diluted gas. My conspiratorial mind was wondering if this might actually be a conspiracy by the big oil companies to counter everyones revulsion to high gas prices and their decision to drive less, thus consuming fewer gallons overall. It seems as if they're saying to the mass populace..."So, you don't want to by gas? Well, we'll just make it so you have to buy it more often, and we'll still get your money! (muhahahaha...evil laugh)."

More than likely, it's just one station. I tested the theory and at about 1/2 tank put in premium from a different station. Ah Ha! There was my old reliable 41 mpg...at least for the first 50 miles...then whamo!, right back to 30 mpg. With more fill ups using premium from the other station, I'm hoping to purge the old gas and replace with new good gas, If this fixes the problem, then great, no worries.

I have also noticed that my IMA batt seems to always be in charge mode. I've not documented it, but it seems to always be on. My wife drives the car, about 50 miles/day in town. Here in San Diego, it's hard to go anywhere without getting on a highway for 10-15 miles, so there's a mix in driving. We've been thinking of taking a long roadtrip to get the IMA batt good and charged to see if all the local driving is the promlem. Seems like it could be tiring out some of the IMA cells, causing a disproportionate amount of recharging and a constant load on the engine causing poor gas mileage. However, if this was actually the case, I think I'd see an IMA error light.

After this long-winded ramble...my question is...Has anyone else seen a drop in mpg that could be attributed to a weakening IMA batt (no error light yet)?

Can this situation occur without the IMA sensors reporting an error light...i.e. Check IMA?

I'd appreciate any thoughts and experience on the issue.

Thanks,

Trebor33

Wow, that sure is a sudden change. I would suspect bad gas also. Was it an ethanol blend or something?
Your idea of taking a long road trip sounds good; at the very least it would use up any suspected bad gas. I agree the worst mileage would occur in stop & go driving, but if that's what you've been doing before, something else must be causing the sudden drop in mpg's.
The fuel door has a locking mechanism, so it's unlikely that anyone could have siphoned out any gas. Maybe check your tire pressures. One time I found one of my tires was very underinflated compared to the others.

http://www.greenhybrid.com/compare/m.../car/5679.html

It could be a combination of both fuel and battery. If the battery is not charged sufficiently or not holding a charge (constant charging) that means the ICE is being used more and more to get you going, thus using more fuel. I also have an 05HCH and the battery seems to be doing fine so far. It always charges back up to full. What I have noticed is my mpg's are better when I use 89 midgrade fuel from a brand name company. with reg 87 I get about 45-48mpg but with 89 it averages around 50-52. Tried a discount brand 89 and it was the same as using reg 87....Hmmmmm, sounds like that station had a "bad" mixing valve, or were they just charging more for regular when you pumped 89??? Very fishy to me.. needless to say, I don't go there anymore...

Just wanted to expand and thank those that responded.

I concur, gas could be a problem, a tank or two from another station will sort that out.

My real concern is for the constantly charging IMA battery. If I'm always running with a charging load on the engine, this would bring my mpg down drastically, wouldn't it?

However, my hope is that if this is the case, the computer is smart enough to recognize and announce a weak or failing battery with an IMA failure light.

So far, no IMA light.

Therefore, I'm asking others to see if anyone else has seen a similar drop in overall mpg.

BTW, I mentioned CA gas additives. I purchased my HCH in Indiana and there consistently got 45-48 mpg. I saw 54 mpg once while driving cross country. However, when we got to San Diego, the mileage took a big hit. What gave me a clue that it may be gas additives was my BMW motorcycle, which I purchased in San Diego and took with me for my two-year hiatus in Indiana. In CA, my Beemer got a steady 42mpg. In Indiana, it suddenly jumped to 50mpg. This was about a 20% increase. The only explanation I could think of was the MTBE (or similar) additive that suddenly wasn't in my Indiana gasoline.

Taking my Indiana HCH and my Beemer back to CA seemed to confirm my theory, My Beemer dropped right back to 42mpg, and my HCH mileage dropped to 41mpg. Not quite as big a change as my Beemer, but significant enough to notice. Granted, the highway speeds in Indiana were 55-65 miles per hour (strictly enforced), whereas in San Diego, the highways speeds are 65-80 miles per hour. The overall faster speeds play havoc with fuel efficiency, especially since the HCH sweet spot is around 52 miles per hour. I'd expect some mpg drop for the faster highways speeds, but not for local, non-highway driving where the HCH is touted as performing better than highway. I was never able to prove Honda right on that one.

Seems criminal for the state to steal that much potential energy savings from its citizens through a mandated gas additive.

My battery seems to like staying at around 75-85% of what it shows on the display. Other times, even if it is half, it is charging. For it to ever get that high though, the weather cant be too warm and I need to drive on fairly level road for about 5-6 miles. The difference you are seeing could be due to bad roads in CA. I live in the bay area and the few really nice roads that we have give me a good increase in FE.

Faster speeds ruin MPG. Period. Hondas also do NOT do better in heavy stop-n-go driving than on the highway. I get under 40 in heavy stop-n-go, yet near 50 (or sometimes over) on the highway. On that same highway, if I zip along at 70+ MPH (instead of 60), my MPG drops to low 40s.
Yes, a constant charging situation will hurt your MPG. That sounds like a problem to me. It could be a sensor or something. You're probably going to have to get it looked at, unless this "bad gas" scenario clears it up somehow - which I doubt.

Steve

STOP terrorism - Drive a HYBRID

Vehicles:
350 miles a week ------------ 2006 HCH II, Magnetic Pearl, w/NAVI (born on May 25, 2006)
350 miles a month ---------- 2003 Mazda Tribute ES-V6
350 miles a year (for now) - 1986 Mercedes 560SL