Gen3 warming up stages

Looking over the warm up stages for the GenIII and how they differ from the GenII I cannot determine whether it would be beneficial for me to allow my car to warm up in the garage before leaving on my morning commute or not. I know the usual answer to this is no. But because I live less than 1/2 mile from the freeway the engine coolant is usually below 130F upon entering the freeway. I the speed up to 60-65mph.dropping back down to below 45mph to enable the idle check ceremony would be difficult if not dangerous. So due to my proximity to the freeway and the low engine temperature upon entering the freeway, would it be better for me to prewarm the car and try to enter S4 before entering the freeway?

My commute is 47 miles long and all but about 1 mile of that is freeway driving at 60-65mph with no stops.

 

I think some of our Japanese posters have said warming the car up for the first 50 seconds or so before driving might actually save fuel. The reasoning is if you take to the road without warm up time the ICE supplies no power to anything because it is running with retarded timing to warm up the converters and the ICE itself. Therefore if you are driving you are running on the battery until the ICE has run long enough to get out of stage 1a. That power has to be put back in the battery and due to conversion losses you use a little more fuel.

If you put your foot down far enough the ICE will supply power to propel the car even in stage 1a but this is not good for the engine.

This makes good sense to me but I suppose it may depend on where you live in relation the highway also. For example I live about a mile from the nearest main road so I can creep along until I'm out of stage 1a with no problem, but I'm probably using extra fuel when I do.

 

As long as your up past 103F, you are good to go Justin. The question is how fast do you drive before you get on the freeway?

 

This morning I allowed the car to warm up a bit before leaving the house. I started it and went back inside the house for coffee. By the time I came back out the car had cycled the ICE once and the engine was off when I got inside to leave. Total warmup time of less than 2min. The ICE coolant temperature was at 103F (outside temp of 37F) as I started driving down the road. My speed is approx. 35mph for a little more than 1/8th of a mile. The other 1/8th mile is residential so I am doing about 20mph at most. From there I jump directly on the freeway at hit 65mph.

 

Even if you defer stage 4 until slowing on the exit ramp, I think you will be just as well in stage 3 on the freeway. If traffic backs up you'd get stage 4 sooner. I suspect it is about a breakeven on fuel economy, though Ken1784's advice to let it idle likely has a slight edge.

A block heater would be great, but unlikely to make financial sense, and possibly not convenient for you.

Note that the gen3's do not need to stop to get stage 4, just a prolonged glide below 45 mph iirc. Not that you should hold up traffic. Stage 4 really is == stage 3 on the freeway. Even Stage 2 will suffice on the freeway absent stop & crawl, in which event you'll get to 4.

 

I agree with spiderman, getting to 103F and 50 seconds of 1a time before the on ramp is key. Even 1b is fine for freeway. Its really the ~50 seconds that gets you out of 1a, even if still under 104F.

 

Yeah, assuming you live on a little-traveled residential road, the best tactic is to use minimal propulsion during the first 50 seconds while the engine is running, accelerating ridiculously slowly, only using the 1.5 kW or so that the engine provides during S1a, no more or less. After that point, just get on the highway. The only thing S4 really buys you, as far as I'm aware, is being able to stop the engine more easily when you let off the throttle; since you can't do that anyway on the freeway, there's not much point to getting to S4 beforehand.

On the other hand, maybe we're all wrong - so feel free to experiment a bit, and see if the GPH changes when you're cruising on the same chunk of road depending on whether you're in S3 or S4.

 

I'll start experimenting once the weather clears up. We are in for a week or so worth of rain which sort of ruins my plan.

Thank you guys for all of the information.

 

I use the Scangauge IGN to monitor the change from Stage 1a to 1b. The ignition timings go from negative to positive, typically from -5 moving up to -1. Once positive, you are in 1b and probably good to go without waiting for 1b to complete at 103F (40C). I have seen 1a complete at under 90F (32C) and in less than 50 seconds. You can also hear a slight change in the engine sound when this happens.

From the description of your commute, this short wait (or no wait at all, but just go really slow keeping RPM at 1280 and BTA under 30 or as little as possible) is probably going to give you all the measurable gains that you are likely to achieve.

 

I have seen the change in timing and the change in engine sound you mentioned, also slight change in RPM and if you monitor high voltage battery current it will usually switch to charge at this time.

 

Does anybody have any information about whether the described stages are different for the plug-in?

 

Yes. They've changed the units on S0; it now ends after 12 miles, not 12 seconds.

 

Heh.

Well, unless you want to start the engine early because you have a lot of hills near your house and want to get that first minute of lower power/more engine wear out of the way... or you want heat... or ...

 

As a new Prius owner (2010 III), this is really intriguing to me.

The morning temps where I am average about 40-50 F during the summer.

Should I wait until the engine shut's itself off during the initial start up? Or can i just drive it right after I start it?

Looking for the least long term wear on the components...

 

Just drive off if you want to, but don't use to much throttle. If you push the pedal down to far it will start using the engine for power and may rev to high for a cold engine. If you watch the HSI keep it out of the power zone to the far right until it warms up a little and you should be OK. If you have a ScanGage you can watch RPM and hi voltage amps and have a better idea of what is happening.

 

Thanks Tom. Can you explain the high voltage amps a bit? Is that when the HSI is at the peak of the battery section (pretty much right at the middle line)?

 

No, high voltage amperage is simply a measurement of how much current is going into or out of the HV (traction) battery. Before the car gets out of stage 1a it uses the battery even thought the engine is running, this allows retarded timing and the engine warms up faster. But if you put your foot down to far it will require more current from the battery than can be provided and the engine will provide the extra, even before it is warm enough to do so. This may not hurt anything but I don't like to do it because it probably puts extra strain on a cold engine.

I mentioned the HSI above because it does give some indication of how much current you are asking for, i.e. if you stay out of the power zone in stage 1a you will normally not require power from the engine until you are out of stage 1a. The HSI is primarily an indication of how much power you are asking for or how much you are putting back into the battery with the regenerative brakes. Here is a good writeup by Hobbit on the HSI: HSI

 

+1 to just drive it. Keeping the throttle very low (e.g. ~1/6th of the wide part of the HSI) during the first minute of engine operation will use about the amount of power that the engine is producing, but gives you very limited acceleration. This may slightly improve your mpg, and will reduce the load on the battery (but probably not by an amount that would make a noticeable difference in wear and tear on the battery).

Personally, I use that first minute to slowly exit my (longish) driveway and get onto the slow residential roads; about the first time that I really need to accelerate (from a stop sign just past the end of the driveway), I can hear the engine change pitch a bit, and the engine will rev higher to provide most of the power. (I can also see the change on the ScanGauge via RPMs and battery amps.)

But just driving it won't cause any undue wear on the car, so don't fret.

 

I just drive my Prius very slowly while it's warming up, like I would do on any regular car. With the added plus that the HV battery doesn't really need a warm up like a conventional engine, just to push a car out of a driveway and onto residential streets, so there is absolutely no stain on any mechanics or electronics (they, really don't need warm up a all).

After 50 secs the engine noise changes and I take that as a sign that I can accelerate just a tad more if necessary. I usually wait (and I can do it most of the time) a couple of minutes before accelerating more decidedly. But like on all cars, I wait that a few mins have passed before pushing it further, so that te ICE is properly warmed up, and on the Prius, if the heater is off, it is usually really fast (1-3 mins) compared to a regular car. Since there is no "cold" light, I usually use a stop to see if the ICE turns off. If it does, it means that it is warm enough.

I can understand though that those living really close to a highway would need to warm the car from a stand still before driving off elsewhere on it.
I have noticed that if I let the car sit (for any reason) while it warms up, the fuel consumption on my regular 10mi commute is higher, especially at my "check point" after 3km. If at 3km the average fuel consumption is at 7L/100km, it means it is going to be a good day... if at 8 or higher... not good
So for me, letting the car sit while doing a warm up cycle, is not only prohibited by law, but it does not bring any FE benefit at all, as otherwise suggested by others on these forums and also as common sense would indicate.