Dropping Mileage/Battery Damage?

<div class='quotetop'>QUOTE(Popeye @ Sep 7 2006, 12:13 AM) [snapback]315587[/snapback]</div>

On reflection, I only have several negatives and just one positive thought to offer, but I'll offer them all anyway.

Other threads on this board have discussed significant mileage drops after memory re-flash, presumed to be due to loss of data tables that the on-board computer cumulates and then uses to optimize the running of the ICE, for the particular circumstances under which the car is being driven (age, fuel, air density, temp, etc.) This is not unique to the Prius but will affect almost all modern cars to some degree. My Ford, for example, loses its memory whenever the 12 volt battery is disconnected, and has to fumble around a bit for the next few starts until it learns how to idle smoothly again. I don't know whether or not a simple 12-volt disconnect will force the Prius to lose that accumulated data, and 5k miles is plenty of time to re-aquire it. So, loss of "memory" might have occurred and might have depressed city mileage for a tank or two, but would not explain extended mileage losses.

On the concept of a gas leak, I think you can rule that right out, if you are reading the mileage off the MFD and not calculating it based on fillups. My understanding is that the gas guage and the gas mileage are separate concepts on the Prius, e.g., if someone siphoned gas out of your car, the gauge would drop (measured by tank sender) but mileage would not (calculated by computer based on amount of fuel that has been injected into the engine). I could be wrong about that, but that's my impression.

If the frame is bent enough to give significantly higher rolling resistance, you ought to see unusual wear on your tires by now, e.g., if you're grinding down the tread on the left rear tire enough to drop your mileage this much, that tire ought to look noticeably different by now. Measure tread depth on the two rear wheels to put this issue to rest, I think.

I can only think of one redneck (non-shop) battery load test that might be repeatable across cars, which would be to get two '05s warmed up, leave all accessories off, count the battery bars, flip the AC to max cool with recirculate, and see how long it takes before the ICE comes on. Repeat a few times to get an average. I don't think that would be terribly temperature dependent (because you're asking for max AC output regardless of temp), but I'm not sure of that. In any event, you can see what I'm after -- using the max AC as a standard battery load, getting several '05 owners to try this to see whether ICE-restart times appear consistent, and if so, to proceed.

That'll only test battery capacity at slow drawdown, not maximum discharge rate, but it's something. But if we could get a half-dozen '05 owners to play along, and if the time-to-ICE-restart were reasonably consistent (conditional on battery SOC), and if yours were the clear low outlier, you'd have a case for taking the car back for a systematic battery load test. You have a case for taking it back for an evalulation of the battery now, but this might provide enough to get the dealer to take the issue seriously. I mean, I have to assume that the Prius can accommodate reduced battery capacity as the battery ages, so a "prematurely aged" battery wouldn't necessarily raise red flags, would it?

Ah, actually, arguably the better test, less dependendent on original SOC, is to turn on the radio first (because this test is going to take a while), turn on max AC recirculate, ignore the first ICE startup, then track the 2nd through Nth intervals between ICE run times. Might as well track ICE run times as well. A combination of short ICE runtimes and short inter-ICE-run intervals would both suggest reduced battery capacity.

In a nutshell, I'm suggesting that you get the car thoroughly warmed up, then sit in your car for an hour with the AC on, and track the times at which the ICE turns on and off, with max AC on recirculate, and radio playing. Toss out the first startup: so, start the one-hour clock from the moment that the ICE shuts down the first time. Then, calculate mean ICE run time and mean inter-run-time interval. Record the exterior temp while you're at it, I guess. Get half a dozen other '05 owners to do the same. See if your run times and inter-run-time intervals are noticeably shorter than others'.

In an even smaller nutshell, if your battery is really hosed, it ought to be enough merely to count the number of ICE restarts in an hour. Shorter invervals = more restarts in a hour. That signficantly reduces the data reporting burden, if we can get someother owners to cooperate.

So, drive 10 minutes, then sit in your car, listening to the radio, with max AC recirculate on, start the clock after the first ICE startup/shutdown, and count the number of ICE startups that occur in the next hour. Oh, make a note of the tempeature, too. That's not a big strain. Then, e.g., if everybody else says 7-9 per hour, and you say 15, then yeah, that's your problem right there. (And if everybody else is all over the map, the test is useless. )

If the technical experts on this board think the max-ac battery load test is plausible, then I can at least see if I get consistent ICE restart times, running max ac recirculate, in my '05 this weekend, and report back to you. If there's a lot of variance for an individual car, I'm less convinced that this is a useful test. I'm hoping that a knowledgeable reader will chime in here with further advice.

 

Well, chogan gave you a lot of work to do there, and I agree that these are good ways to confirm that the HV battery is still happy. But for all that, you could just go to a Toyota shop and ask them to measure the internal resistance of each module with the THHT. If all modules are close and like 30 milliohms each (I am stealing Hobbit's data there), no worries. They might want to charge money for this, but you could try to bribe the mechanic with a bag of cookies. I have had good luck with that approach.

Not quite ready to abandon the 'bent-frame' idea though. One would hope that checking for this would be an integral part of the rebuilding process, but one never knows... It could certainly be more noticeable at low-speed driving than on the highway, because rolling resistance is a bigger slice of the 'energy pie' at low speeds. It is not hard to measure frame skew to within 1/8 inch yourself, if you have a nice flat smooth floor and are willing to get on your knees and measure the diagonals very carefully. Wanna know how?

 

<div class='quotetop'>QUOTE(tochatihu @ Sep 7 2006, 05:09 PM) [snapback]315948[/snapback]</div>

Agreed. Far better to get the shop to test it properly. I only suggested counting recharge cycles /hour under AC load as a plausible (but clearly inferior) do-it-yourself test.

 

That sucks, that would really piss me off. If you need any data I can get from my 06 (I can do the AC thing or whatever) let me know, i'm more than willing to help.