Odyssey owners... HELP!!!!

[Brian B-P]

...Could it be where the Odyssey was built?

The assembly plant is likely relevant to quality control, but to me that just means a vehicle coming out of the less-desirable factory is more likely to have a fault; the extremely poor mileage of this vehicle seems like a fault, rather than an expected characteristic which varies by assembly location.

The Japanese manufacturers have been very careful to avoid wrecking their reputations for quality by falling to standards of their additional assembly locations (such as those in North America), but they have also been careful to avoid placing products from different countries side by side. At one point, Honda assembled Accords for the U.S. in both Japan and the U.S., but only supplied areas east of the Mississippi with U.S. product, and areas west of the Mississippi only with Japanese product: no one was likely to put them side-by-side and point out detail differences.

Anyway, if one source tends to produce a particular defect, that might be a good thing to check for on a specific vehicle. The origin should be on a placard, which I think is likely on the door jamb.

[Kurt & Ann K.]

RogerH,
Is it possible that the two vehicles' have different differential ratios? That can make an enormous difference in fuel consumption.
Kurt & Ann K.

[Brian B-P]

Final drive ratios are still an optional choice on trucks, but rarely in other types of vehicles - the design is too highly integrated to allow the buyer to change just one component. With a pickup (or some SUVs), I think this would be a good thing to consider.

The effect of a very low (numerically high, lots of reduction...) final drive would be similar to driving in a lower gear, which seems to be the common guess for the source of the problem

So, Roger, it's been a month... any progress?

[Roger H]

Well interestingly, I just spoke with my folks about this today and I hadn't seen the new posts here!

Apparently with this last tank of gas, the mileage jumped up to 27mpg where it ought to be. Honda is still looking into figuring out what's going on. This is turning into a really bizarre kind of problem. I'm beginning to wonder if it's a programming issue and the computer is only working part-time and goes back to it's defaults when it doesn't work. In other words, it runs ok, but not optimally when the system is goofy. Just a thought...

Regarding the final drive ratio, you can specify your ratios in a conventional rear-wheel drive vehicle. For example, my Excursion has 3.73 gearing. A friend here in town had one with a 4.10 ratio and his gas mileage was half what I get with the same engine, the V10. Anyway, I don't think you can change the gear ratios in a transaxle; at least I've never heard anyone discuss it in those terms.

Thanks again everyone for your great suggestions! I've passed them all along to my Dad to explore with the dealer.

Roger

[Frederick L. Simson]

Apparently with this last tank of gas, the mileage jumped up to 27mpg where it ought to be.

I just did a round trip from Palm Springs, CA to Lake Havasu City, AZ today. My Odyssey went about 450 miles on one tank of gas (not towing), a little less than 17 gallons. (The yellow fuel idiot light was on for about the last 50 miles.) It figured out to be 27 mpg also. Mine is California emission equipped.

[Brian B-P]

A variety of final drive ratios are often available in the same transaxle, to suit the needs of different models, engines, or option packages; however, the choice is rarely offered to the retail customer. There is less room (literally) to arrange a different ratio in a transverse transaxle than typical separate differential housing so the ratio choice isn't as wide, but in both cases there is a small driving gear and a larger driven gear (these are the pinion and ring in the regular diff) and the relative sizes determine the ratio.

In a combination which I find interesting, according to the Honda Canada website the Ridgeline has a 4.533 ratio final drive in the front, a 0.537 transfer gear, and 3.384 final drive in the rear. The front and rear axles would need to go at different speeds, which I assume is required for Honda's slip-clutch power distribution scheme (VTM-4®) to work. The Pilot is allegedly built of the same family of components, and the Odyssey certainly uses the same engine (and likely a variation of the same transaxle) but we can only guess at the gear ratios, because Honda only shows the ratios for the pickup truck; truck buyers apparently care about gear ratios.

In passenger cars, even ones with "conventional" rear-wheel drive, choices in final drive ratio are much less likely to available than with trucks and SUVs.

Anyway, Roger's parents' Odyssey certainly didn't grow a new gearset by itself, so that isn't the cause...