Prius gen 3 help

Yeah it could be related to declining ICE power with age, but I think even more so it's declining battery power that exacerbates it. My 2005 gen 2 is at 210,000 km (130000 miles) and to be honest the engine stills feels really good. Very little oil consumption and I can't say I've really noticed any decline in power over the years. In contrast however, I have clearly noticed a decline in the battery's capability over that time. I particularly notice that it reaches full charge much sooner on descents, and it also sometimes unexpectedly "drops bars" abruptly - as if the battery ECU suddenly realizes it has the SOC wrong and readjust to a lower level.

Even so I've only had this situation a couple of times. The most recent was ascending a large mountain pass, only about 80 km/h speed limit and with sharp 20 km/hr "switchback" type bends. I got the sudden unexpected drop of SOC thing happen and suddenly I'm trying to pull out of these 20 km/hr bends and accelerate back to 80 (km/h) with the SOC on about 1 or 2 bars. Trying to accelerate hard from low speed without electric assistance is really sluggish on the gen2. Normally the electric motor kicks in quite a lot of torque at low speed, and you really don't notice how much it does until it's not there. I was seriously struggling to get back to about 60 km/h before the next bend, while other cars were passing me pretty easily at the roads posted speed limit.

 

I have the same experience whenever I travel to Las Vegas from Los Angeles. There are a few 10 mile stretches of uphill climbs, followed by 10 mile downhill grades. The uphill will drain all of your battery power and it's very difficult to maintain going 65mph or higher. It just seems the engine is really struggling to maintain that speed. The downhill part that follows will charge the battery all the way up to 100% and then some.

Often on the uphill stretch, I would take it off cruise control (which is set at 73) and just manually go around 65 up the hill. I feel it's very hard on both the engine and transmission when the car has to work that hard going uphill (without much power).

 

I read about this issue in gen 2 in many reviews and made sure gen3 was improved in this regard before buying my 2010 one.

To me it sounds like poor programing logic for the ECU to let highly depleted battery while going up steep grade at hwy speeds. When battery is depleted, the ICE power is then diverted to charge the battery causing the OP's problem.

But, I do little high elevation/steep hill driving to test the limits of my 2010 prius.

Last time I drove in Rockies it was a nearly fully loaded mazda protege with 108 HP engine and it struggled a lot to keep speed at 70 mph IIRC. Eventually, the tranny overheated and I was stranded. It took more than $3000 to fix the car. It was a memorable trip.

 

Can you source that? I've never seen any credible information that suggests that there's an appreciable loss of power as an engine ages. I'm highly skeptical that it's anything meaningful, especially as much as 50%.

Something I forgot about before is how much power is lost at altitude due to decreased air density. Rule of thumb I've read was somewhere around 3% per thousand feet. So if you're at 10,000 feet high pulling up to the Eisenhower tunnel on I-70 you would be down 30% of rated power. It now makes sense how the ICE wouldn't have enough power to pull up a grade if it were significantly above sea level.

 

Yeah, you might expect some amount of power loss in an older engine if the compression was down a little, but I'd be thinking more like 5 to 10 percent rather than 50. To get something like 50% loss you'd need something drastic like loss of firing on a cylinder or two. Very unlikely in an engine that's anything close to a roadworthy (passes state inspection) operating condition.

Yeah, that's part of the problem for sure. The ECU does a good job of looking after the battery when it's new, but a degraded battery does seem to confuse the ECU sometimes.

Several gen2 owners (myself included) sometimes get an "undershoot" type condition with their SOC now that their batteries are aging. This behavior typically occurs after the SOC has been relatively high (7 or 8 green bars) and is on it's way back down. Frequently under these conditions there is an abrupt (almost instantaneous) loss of SOC, for example from 6 bars to 3 or 4, for no apparent reason. It appears that the state of charge management simply starts falling over once the HV battery is a bit degraded.

By way of analogy, it's a bit like the reported SOC that you might get on an aging laptop. You know the one that reports 100% SOC and 180 minutes estimated run time straight after a charge. It then run flawlessly for the first 90 of those minutes, but then at about 90 minutes the SOC takes a sudden dive from 50% to 5% in a couple of minutes. I'm sure many of us have seen that type of behavior in a laptop with an aging battery.

 

I guess I would be really surprised to see 50% power loss in an ICE assuming it has been maintained appropriately for its age/mileage. Pretty much everything I can think of that would lead to significant power loss is meant to be cleaned / tuned / replaced. Don't have a lot of data, but my '05 Prius with 100k miles still does the drive above just fine, and my previous '89 Saab 900 turbo at 20 y/o w/200k miles still did 0-60 in about spec time....

IMHO battery aging may be part of it, but this operating condition has existed since new. Its always been my experience that good sustained performance on long steep grades does require active engagement of the drivers brain, relying solely on the ECU will often get you into trouble. Poor programming is a little harsh, bearing in mind that the Gen 2 Prius was being developed in 2002-3 when hybrid technology was much less mature, but the net effect is the same. As far as I know this was typical of most if not all hybrids of the day.

Even with an older battery / engine / vehicle, the best advice I can give is pay attention to what the battery is doing and keep yourself from getting into that low power state. That should not require having to slow down, you just need to keep the battery either doing nothing or charging.

 

Mine feels like it struggles to go up long hill climbs. I drop down to 50 going up what's called the Sunol Grade here in the Bay Area. Haven't tried pushing it to see how fast it can stay (still < 800 mi on the odo at the time) or seeing if it would drop down to an even slower max speed on a longer climb of the same grade. My feeling was it'd be the latter..

 

Maybe you haven't spent much time in areas where they run their cars until they are 40 years old and HAVE over 200,000 miles.

You can usually spot them in the mountains.
They struggle to go 40 MPH uphill and have a fair amount of smoke pouring out the back.

My source........having been alive for 67 years.......and driving and wrenching most of them.

What do you really THINK is going to happen when the valves don't seat good anymore AND the rings are shot so that half the compression (or more) is gone and the plugs are oil fouled ?????
Doesn't common sense account for anything anymore ??

(Maybe 50% wasn't a good example but it is not unheard of.)