What is the fuel consumption of the Gen 3 when the ICE idles?

I haven't watched this on the Prius, but suspect that it will be quite variable during the warmup cycle. Will have to remember to check it sometime.

For reference, my 2.5L Subaru starts at 0.8 gallon/hour, declining to 0.3 gal/hr when fully warmed.

 

You might consider parking the car with something on the trip meter and calculate the fuel burn. The next day, start the car and wait for the idle warm-up to complete. Use the updated reading to calculate the fuel burn. Subtract the two.

Bob Wilson

 

You are correct, Sir.

I have GPH (gal per hour) as one of my Scangauge choices and the rate varies drastically during the warmup period. It also varies depending upon how you drive away during the warmup period (I typically start to move before the ICE fires up).

 

Some Prius numbers this morning:
At startup, 39F, 0.68-0.72 gal/hr (it actually started at about 0.62, then rose after moving out of the parking space);
80F, 0.44 gal/hr
100F, 0.35 gal/hr
130F, 0.30 gal/hr just before the first AutoStop. Hitting the defrost button forced it back on at 0.31-0.32.

After that, AutoStop prevented any more idle measurements.

I was surprised to not see any smaller numbers than my larger non-Atkinson Subaru.

 

Of course, in the real world, an idling Prius would not be idling 100% of the time like the ICE only Subaru. So the actual consumption per hour should be less.

 

Yes, my Prius is a GenIII.

My Subaru burns more fuel in a fully warm idle than your Polo burns during a cold starup.

The Subaru burns about an extra 0.2 gal/hr when the AC compressor clutch kicks in, but I have never measured its duty cycle to learn what fraction of the time it runs.

 

I guess you should put the car in neutral (N) before making the measurement. When the car is in D, B or P and the ICE is "idleing" (not powering the wheels, car stopped), the ICE is not idle at all: it recharges the battery. And while it does so, it provide lots of power to MG1. Thus, the ICE is using more gas than a normal car would use when stopped in D, B or P. But it does not waste it, as compared to other cars.

 

For some reason I hadn't previously thought to check in N, but it does lower consumption when this prevents battery charging.

Today I didn't try N on the dead cold engine. At room temperature, it pulled 0.50 GPH. Then it fell to 0.33-36 over a wide range of different partially warm temps, and 0.20-22 when fully warmed. There could be an offset in there, as my Scangauge sometimes displays a 0.02 GPH during autostop, instead of 0.00.

I'll have to watch several more warmup cycles to see if there is more detail to be recorded.

 

hmm, i can see why the prius can be used as an emergency fuel generator now. could last a good while with the engine turning on and off

 

I agree. It is stupid to fall at 0L/100km when we are at infinite L/100km. But I guess some people would complain to Toyota that their car is inefficient when it is stopped at a red light when they would see their IFC topped at 10L/100km. It would be cool to switch to L/hr when we are below a given speed (5 km/h or so), like some cars do.

 

In the evening it is a low speed run through the parking lot to a traffic light. Waiting at the light I've seen up to .7gph (2.6 lph) but it is not constant. Generally I'd say the range is mostly .5-.7gph (depending on the OAT) but it swings up & down every few seconds.

 

If I just compare effective intake displacement against my Subaru, this Prius does seem to burn a lot of fuel while idling.

But others have pointed out that during cold idle, it is configured to produce extra heat, so this would consume extra fuel. And I find it doesn't idle for long, certainly not 5 or 10 minutes.

I have two choices for the start of my commute route. On the steep descent route, down a 130 meter hill, the last idle occurs at the 2nd stop light at about 4 km. The other route has much less descent, so the last idle occurs at the 5th light, at about 2 km. Beyond those points, the engine has been warm enough to go into AutoStop, so it burns no more idle fuel.

 

This is not correct. While standing still, if you are burning any fuel the L/100km rate is infinite. This is because you could idle there forever at zero speed without ever covering the 100km. Another way to look at it is the distance traveled is zero, so the denominator is zero. If the numerator is non-zero, which it is with the ICE running, then you have a finite number divided by zero, which yields infinity.

If the ICE is off, then the fuel burn is zero. Standing still with without burning fuel yields zero divided by zero, which is indeterminate.

Tom