How To Do A Steep Uphill When The Engine Is Cold

that is correct, but only under extreme circumstances where the ECU decides if it does need ICE torque.

 

I face this issue when I visit my parent's house. I've opted to "force" the car out of battery only mode into the gas engine mode by accelerating well into the power band. Otherwise, I'll drain my battery down to 2-3 bars just climbing the stupid hill.

 

I'm at the bottom of a very steep driveway - about 50 metres to reach the street; short but steep enough that a =<1.3L sedan with 4 adults in it probably couldn't climb it.

Is there a way of forcing the ICE to idle on startup (does putting it in 'N' with the handbrake on work)? It doesn't get too cold where I live so a minute or so of combustion would probably suffice. I doubt the battery alone would get me even ten metres up the slope.

 

On a cold start, if you put the Prius into Neutral mode instead of Drive mode you can delay the Prius turning on the ICE to warm up the car - if the Prius' parking brakes are not on and you are not pressing the brakes - the Prius can be pushed out...

On a cold start, the Prius will always start the ICE in Drive mode but it will automatically turn the ICE off after the coolant gets to 103 degrees Fahrenheit. Should the coolant temperature drop below 100 degree fahrenheit afterwards the ICE will automatically restart just to keep the coolant warm.

For steep hills, setting the "Power" mode should help with throttle response time.

 

The first warm-up begins when the engine first runs and the two oxygen sensors are too cold to operate. It lasts about 45-55 seconds until the oxygen sensors, one in front and the other behind the catalytic converter, return voltages needed to adjust the fuel trim (i.e., the mixture.) During this time, the engine operates in "open loop" mode using stored injector settings . . . inefficient settings. Oxygen sensor temperature, not time, defines this interval.

Once the oxygen sensors begin working, they are used to adjust the fuel trim, the mixture, in "closed loop" mode. Based upon the coolant temperature, the engine will operate fairly efficiently until about 60C. Thereafter, the fuel trim stays in the optimum range for the catalytic converter. If the engine cools to the lower 60C range, it will start to keep the coolant warm, typically 70C. Again, no time but temperature defines the limits of this warm-up.

Bob Wilson

 

Interesting fact, Bob!
Seems like a potential DIY oxygen sensor induction heater project/experiment!

 

yes, you press gas pedal while in park.

 

Simple, I like it

 

I have no advice here.
Just would like to say, one reason I like Prius Chat, is I've seen less analysis of how to best reach a summit employed by teams trying to reach the top of Everest.
You guys are amazing.

 

Start the car, put in power mode and drive up the hill and go to work. If the engine blows, I'm sure Toyota would likely exchange it. Otherwise it temp wont make that big a difference over the long haul.

 

I have a short, winding pinch of a hill to climb in the mornings.
Even with an Engine Block Heater, the engine will go through the open loop-closed loop/ negative timing-positive timing rituals mentioned by Jon and Bob. (Unless you've cooked it to over 60°c!)
So unless the engine is warm from a previous run, there will be a period of up to 55s where the engine is trying to warm up as cleanly as possible at the expense of fuel economy. During that time, you can't ask much of the engine and the HV battery will just drain. Oh, and keep the heater switched off.
(Before you wonder why the Prius imposes such limits, try driving a standard ICE car at that temperature up that hill without any system limits and see how much metal is in the next oil change!)

Driving up the hill is a good way to get heat into the engine to reach the next stages.

BTW, Jon and I live in Australia where you can't even buy an engine block heater and we've had no problems with Toyota. Australia doesn't have an equivalent to the Magnuson-Moss laws, but Toyota is still OK with an EBH.

 

I second the block heater! I think all comments so far ignore the elephant in the "room" - cold motor oil does not lubricate sufficiently to avoid unnecessary engine wear, especially if the engine is put under significant load like hill climbing. In my mind, that far outweighs theoretical best gas mileage for that short time. A warm block will help warm the oil more quickly. In these circumstances, I would hold the pedal down far enough after start-up to prevent auto shut-off and allow the engine to idle for a couple of minutes, and then climb the hill as slowly as practical to minimize ICE RPMs. The little bit of extra fuel consumed is worth the kindness to your engine IMO.

 

Do you see low speeds / power trying to climb a hill on a cold battery?

 

I have a 550 feet at 1.8 miles climb up to my house. I have a gate and speed bumps which cause lots of slow down and speed up scenarios. The climb is on the way home so my car is warm and therefore the situation is different.... but I have made some basic efficiency observations which may be helpful. First off, my Prius III is only 1,400 miles old and hasn't fully broken in, winter weather has created lots of temperature fluctuations and I'm still learning how to drive a hybrid. But I have noticed the following patterns.

No matter what, I'm going to get dinged for 5-15mpg on this final uphill climb of my 38 mile round trip. I typically average 62-66mpg driving to and from work just before the hill and pull into the garage with 54-58mpg. It's a big let down to put in the effort to go over 60mpg and have a steep hill ruin my work, but anything close to 60mpg is gravy so I'm still happy. See below for different techniques I've tried.

1. 75% to 100% throttle (always in power) is absolutely the most inefficient technique. I'll get hit with a 12-15mpg penalty if I gun it after the gate and speed bumps and try to maintain 25-30mph. Note these are rolling speed bumps that you can go over as fast as 15mph before getting back on the throttle.

2. Barely any throttle (trying to keep it in lower half of eco) and climbing the hill at a 15mph snail pace so I can maintain a constant speed while rolling over speed bumps and thru my gate yield the second worst efficiency results. This technique results in a solid 12mpg hit. It's almost as bad as full throttling it. I've determined because of the steepness and distance, that it spends way to much time bogged down in ICE mode at this slow speed straining the engine and burning fuel.

3. I've tried EV mode only. The battery runs out very fast, within the first half mile of the climb. Then ICE kicks in to recharge the battery while also working to pull the car up the hill. It's a double whammy, very inefficient, just as bad as full throttle and I've also wasted my battery charge.

4. A combination of technique 1 at the very steepest parts and technique 2 at the least sleep parts seems to get me an 8-10mpg hit. Powering through the very steepest parts seems to be the most effective way. At 3000lbs, this car is obviously too heavy to efficiently crawl up hills at lower rpms.

5. Doing my absolute best to have close to a full charge before starting up the hill, I've developed a technique I call, "uphill pulsing". I try to maintain a speed of 25mph on the least steep stretches, which places me in the middle to upper half of the eco gauge. I try to stay out of the red power. Then I let off the throttle and coast up to the speed bumps, and as I roll over the bump the car gets slow enough (8mph) to where it allows me to engage EV mode. Then I 75% throttle it in EV until it kicks me out of EV which is at about 12mph. I repeat this step at the gate. At the very steepest part of the hill, I 75% throttle it in ICE which puts me in full power at about 20mph but this is necessary to get thru the very steepest part quickly. I need to do more experimentation with short bursts of 100% throttle at the very steepest parts. I think this could be slightly more efficient. Then, finally, when I reach the top of the hill, I lift the throttle to allow gravity to let the car slow down on its own again enough to allow EV mode engagement. Then I let EV mode pull me over the last steep little bit before it levels out. Then I coast to my garage, usually with a drained battery at 3 bars. The key for me is to use up as much battery as possible without getting so low that the engine wants to turn on and recharge it. It recharges completely when I drive back down the hill the next morning so this is part of the technique. This method will result in a 5-7mpg loss, and therefore the most efficient way I've yet to discover. Having said that, this technique is almost too difficult to do consistently, it requires a level of concentration I can barely tolerate after a long day at work, and nobody can be behind me.


I plan on trying different variations of the 4th technique but the weather is too wintery right now for consistent results.

 

Not just different, the opposite different. But thanks for chiming in.

 

The techniques I've described should be beneficial none-the-less... that's why I chimed in