MPG down/SOC Up?

I have noticed the exact same thing. I used to only get grren bars when going down a long hill. On our recent trip to Florida I'd say I saw green bars except the last one for about 80 percent of the time and this is all flat highway driving with no hills. Lately it seems like the car wants to charge the battery all the time and doesn't use the battery for power as much. I was going to ask the Prius tech about this the next time it goes in for oil change.

 

I noticed this too. I was wondering if the engine MUST run to stay warm, so additional energy is going to the battery. Not as efficient, but still an improvement over non-hybrid.

Nate

 

I have of 45 km (30 mi) commute each way, Mon-Fri. I am averaging 50+ mpg, even with cold temperatures. In the morning (temperatures currently at -3 to 0°C) I drive at 65 mph using cruise control. In the evening one-half of the distance is at 41 mph. I drive at 41 mph because that is the "sweet spot" where a green arrow constantly recharges the battery.

In both directions I end up with all green bars at the end of the trip. The full green usually appears on surface streets at ca. 25-35 mph and always "feathering" the pedal - allowing the vehicle to roll on its own insofar as safe and appropriate and not impeding other vehicles. In effect, not accelerating toward red lights.

Pay attention to what the Prius is doing - the balance between the ICE and battery. Try to strike a balance with a green arrow going toward the battery. This is similar to watching a vacuum gauge on a large diesel truck - if you pay attention, the vehicle teaches you how to drive in the frugal mode.

 

I guess I'm dense LOL If the battery is constantly being recharged, wouldn't that be less effecient since no battery power is being used to propel the car? I'm sure I'm missing something............

 

The answer's easy as 1-2-3-4:

1. cold weather = cold engine
2. cold engine = ICE runs more
3a. ICE runs more = less MPG
3b. ICE runs more = more charge to battery
4. more charge to battery = higher SOC

Not surprising, but disappointing. I can't seem to get over 50 MPG anymore with the cold weather. Driving home today I had a difficult time going into electric mode only. The ICE wanted to turn the wheels. Temps 29F this morning, 34F this evening.

In the old carburated days, I used to stick cardboard in front of my radiator to help warm the engine faster and keep it warmer. I wonder if this old trick will help the Prius keep warmer and improve MPG.

 

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Be thankful you don't get to practice that skill as much as I do. (Though IL does get pretty cold at times.) Here in MN, we see sub-freezing temperatures for pretty much 3 months straight. And there's always a sub-zero week too...

Last year, I was cruising around in stealth taking action photos of the Multi-Display at -13F.

Pretty "cool" eh?

 

What has been happening to me, now with 6600 miles on the car, it is being green 4/10 of my drives now. Just regular driving and green SOC. Another plus, is my mileage is climbing at a nice steady rate, so I like this green SOC thing thats going on.

 

full green is only 80% charged and I suspect that the culpret is the cat not staying warm and if your splashing slush and water on the underside of the car it'll take a lot, read a lot, longer to warm up and tell the computer to trim the fuel to the engine. A bus scanner would tell for sure and on the 2k3 the output from the O2 sensors say's it takes a lot longer to read in the normal range. Another thing that I noticed last saturday was on returning from a trip to the library as I pulled down the alley the temp finally reached 70C and went into stealth and stopped and dropped off the books for the wife and went back to the car and fired it up and the temp was down to 57C, total time perhaps 4 minutes. 70C is the start of S4 if the BSOC is over 55%. It took an additional 6 blocks for the temp to hit 70C again. OAT was 5C. I assume the quick drop was do to heat transfer to the motor housings and PSD.

 

My problem is, when we were in Florida at above 50 F the car acted the same. Just seem like the ICE was running needslessly to just charge the battery or better statement would be the battery wasn't being used enough to help propel the car, it just seemed to me in the warm temp. the battery should have been staying somewhere near the middle and the arrow's should have been showing the battery being used to help prople the car more instead of the battery being charged so much.

 

I think the heater has a large part to play. When I shut off my heater the ICE stops more often for longer times and my mileage goes back up past 50. Then I can't feel my toes and fingers any more and turn the heat back on. If I forget to turn off the AC then the mileage REALLY goes down. It is too bad the car doesn't have a humidity sensor so that the AC only comes on with the heater when it needs to dry out the air.

Is the electric heater powered from the 12V or HV batteries? It seems to me that the heater messed up MPG more than AC, so I wonder. It seems to me that it would be less efficient if powered from the 12V battery.

 

one thought is, how many of you use the heater in the Auto mode? I try to avoid running the A/C compressor anymore than I have to. Even the electric driven one's get all their energy from gasoline, and how it uses that, is entirely up to the temp sensors in the car. I did notice last winter that the heater took a big toll on gas mileage. When the BSOC hits 80% full charge the main computer say's to the MG's don't send any more charge to the HV battery. Not sure exactly on the regulation circut that limits the charge but I found that out on a long hill, when it hits 80% it wouldn't accept a charge of more than about 1.8 amps. Putting it in B resulted in a 18-20 amp draw which quickly took the BSOC down to the low 70's. It's impossible to damage the battery as the comp won't let it get out of the 40-80% range. One day I'll drag it down till it's off the scale and see what the % is.

 

On the PTC heaters I can't find if their 12V or HV. Their location would say 12 as they are intergral with the heater core, and I doubt that Toyota's lawyers would allow HV in the presence of any liquid.

 

The best way to keep heat in the car while keeping the fan off, is to set the temp to where you want it, then set the register to the floor. Shut off the fan, and you'll have ram air heat while you are moving. This works down to the low to mid 20's for me.

 

The way I understand it, is the ICE is running more to keep engine temperature up, not the SOC in cold weather. In hot weather, ICE runs more to keep SOC up, not engine temp. So in cold weather along with coasting and braking regeneration, the SOC can really get up there.

experiment result - 1 day:
after my collision with the dog, I don't have a grill, so I found it easy to put cardboard in front of my radiator to try to keep the engine temperature up. I blocked off about half of the fins. After 1 day, I have to say I am disappointed. 105 miles today and I got 49.7 mpg. Absolutely no change from the day before. same temperatures. I thought if there was some improvement I could try to block off maybe 2/3. But this isn't promising. My 51.4 LTA has already dropped to 51.0 in two weeks. By Christmas I'll be below 50 again.

 

There are two PTC heaters driven by 12V line. They are 300W each.

Regards,
Ken@Japan