I thought I'd read somewhere that the ICE will turn on at 40mph, but for my 2008 FEH it generally turns on at around 23-25 mph on a flat road. And I usually press the gas pedal super lightly, and avoid quick acceleration. Is 23-25mph about par?

 

If I am super gentle, I might get it to 29-30MPH on my 2007. I might get it going a little faster, but I need a little coasting downhill for that.

I think the only reference to 40MPH is that one can get the ICE to shut off at 40MPH as long as the engine temperature is at at least 155*F and by using the brake with a light stab.

 

my 2008 usually trips at 20 mph, unless I'm super patient and conditions are perfect. Most I have seen is 25 mph on EV.

 

FWIW, forced EV operation does 2 things:

1) creates the illusion of efficiency
2) Accelerates wear of the hybrid battery

Note that every joule of propulsive energy ultimately comes from gas. Extended EV operation generally necessitates additional ICE operation to compensate.

 

Interesting points!

You are right that the battery energy ultimately comes from the ICE. Nothing changes that. But it seems to me that if your batteries are fully charged, then it cannot be charged any more, and regen braking won't recoup any energy and will be wasted. So when the battery is fully charged, it's better to use up that energy than to burn gas.

So, I've read the advice "park the car with as little charge as possible" (by using up the charge). That makes sense to me to a certain extent. Because the next time you start the car the ICE will automatically run, and you don't want your batteries to be fully charged at that point (because there would be no "room" to take on and store the charge). But maybe saying "leave it with as little charge" is misleading and/or goes overboard. As long as you use up enough of the charge on the batteries so that on your drive your batteries don't get fully charged, you're not wasting any of the energy that ultimately comes from gas. Maybe the motto should be, "always use enough of the battery charge so that your batteries dont stay at 100%". Would you agree?

And re: wearing out the battery-- I believe there can be wear on the batteries and they become less efficient over time. But in the long term, they seem to hold up quite well (per all those NYC taxi stories), and it's probably not worth worrying about, for the average driver?

 

Batteries are never fully charged even when shown that way on the gauge. The scenario you describe is rarely achieved unless at the end of a long downhill run. The car automatically adjusts its operating profile to more heavily utilize the battery until the target level is attained. This automatically saves fuel by favoring EV over gas.

The advice you read is nonsense. The gas engine needs to run to heat the coolant, so it can operate efficiently, and it is ultimately required for anything but residential or parking lot driving. You are only going to run it harder to charge a depleted battery when the ICE is colder and less efficient - burning MORE gas than if the battery was at the target SoC.

What I don't think you understand is that the car using a very small percentage of the available capacity of the battery. The car attempts to maintain a target SoC for optimal efficiency. When the battery gets high, it utilizes the EV more. When it gets low, it utilizes the ICE more. The target SoC ensures that there is sufficient reserve for both regenerative braking and EV assist for efficiency.

The bottom line is that the car will manage the battery better than you. Conservative driving with the goal of optimal efficiency gets the best results as the car utilizes the hybrid system accordingly.

Re: wearing out the battery, as one who has seen well over 125 hybrid battery failures and have personally owned 8 hybrid vehicles, all of which have experienced hybrid battery failures, I can tell you the "taxi stories" are the outliers and the exceptions, not the rule. Taxis last a long time because they are driven for 8+ hours a day, rack up their mileage in a short period of time and have their A/C run whenever needed.

Note that one of the 8 is a 2005 FEH with 170K. Battery is dead.

Lastly, the usable energy stored in the hybrid battery is typically on the scale of the 12V battery under the hood. Try to imagine using the under-hood battery to propel the vehicle - this will give you a good perspective on the effectiveness of EV-only operation, and it's strain on the battery.

 

S. Keith--

Thanks for all your wrote. I remain open minded about all of this, and am interested in learning how to get the best MPG.

So, you're saying don't worry, just let the car manage EV vs. ICE, and drive normally. So all of those out there who are using various techniques (like "fake shifting") ... you're saying they might see temporary gains in MPG but when you average over a few hundred miles, it still comes out to be around the 30-32 MPG? They're getting the same miles out of a tank of gas, as those of us driving it normally?

 

If you want better mileage, accelerate at a low rate and drive slower.

 

Just to reply to various comments here.

My 2009 FEH will reach 40mph in EV mode on a flat road with light throttle.

It has 120,000+ miles on it and is 8 years old. This summer I have gotten the best mileage ever, typically 35mpg US. (and it's an AWD) This is inconsistent with battery degradation, which would show up as slightly diminishing mileage.

Battery replacements are so uncommon that supply of used batteries from wrecks exceeds demand. Thus, asking prices for used batteries are as low as $400-$700 on Ebay.

The hybrid battery is only used between 40% and 63% of its capacity. Charge and discharge rates are carefully computer controlled to avoid damage to the system. Thus, I don't see any way a driver could cause harm to the battery.

Most attempts to achieve extended EV mode will be defeated by the system's software programming to stay above 40% charge. The best mileage will be achieved with driving slow enough to eliminate most wind resistance, and by giving it enough throttle that when the gas engine is running, it is running in the sweet spot of efficient rpms, which I understand is something like 2600rpm.

Driving too slow in an attempt to maximize EV mode will result in the gas engine running more to keep things such as the exhaust hot, rather than to keep the battery charged. This is why, if I'm stopped too much in traffic jams, mileage will start to suffer because the engine has to run a certain amount just to keep things warm even if I'm not moving.

If you have any choice in the matter, it is best to be moving continuously on the level, or even better, uphill, while the engine etc. warm up. This way the fuel used by the engine warmup is also moving and, maybe, lifting the vehicle. The worst thing to do is to be stopped during warmup, such as at a traffic light. This is why I release the parking brake and put my seatbelt on before starting the engine. I drive off immediately, since sitting warming up wastes fuel, and initial startoff is with the battery providing propulsion and the engine acting as a generator. Regeneration also will not happen if the hybrid battery is not warm enough.

One very interesting thing is that if you run out of gas, and still have available charge in the battery, you can drive slowly on just the EV system until the battery is below the low charge limit.

 

Wow, loads of great info. Thanks!

I wish I could get 35 MPG!

I drive/accelerate slowly, yet the best I do is 31 MPG on highway, and 30 in-town.

Kind of a relief to know that you can't outsmart the battery system software. So I can just drive w/o trying to over-think everything.

But then ... all these hypermilers ... how are they squeezing out > 40 MPG that they show off on w/ photos/videos of their Scangauge?