My ICE gets bad mpg going under 40 mph?

What has been done to the car lately ? What's your oil level at ? What's your tire pressures at ?

 

Is this over the same route or different ones?

If different, can you confirm the absence of elevation changes via Google Earth can give you an elevation profile of a route between 2 points! | PriusChat

 

I've noticed the same thing but really haven't paid much attention to it. I just assume it has to do with the recharging of the battery and how and when torque assist is applied, (i.e ICE while recharging vs. ICE alone vs. ICE with battery assist vs. EV mode) and that charging at higher speeds is probably more efficient. Try driving with the energy monitor on the display so you can see what the ICE and the battery are doing.

 

When the car is still warming up, it is the most efficient ~50 mph. After the warm up it is better to run the battery at the slower speeds*.

*Note: This is dependent on many factors, including length of battery usage, size of hills, speed of battery usage, etc...

 

At 35 mph on level ground you can hold your speed steady in stealth EV mode. You should also be able to do a bit of coasting, depending on traffic.

On 35 mph speed limit roads I swap back and forth between very slowly accelerating in the lower end of the ICE range and holding steady at about 1/2 EV output. Overall efficiency is solid, but I do agree that when running purely on ICE the car prefers 45ish mph speed limits.

 

This is all true... once the car is warmed up. But for his short route, the ICE doesn't have time to do so.

 

My route to work is 7.5 miles, mostly 35 mph zones, some 25, and mostly flat. In anything but very cold weather, I'm warmed up in about a mile and get 60-70 mpg there, and 65-75 mpg on the way home.

 

All things being equal, it's easier on the ICE to maintain the momentum above 40mph (up to point) than at 30-35mph. Since you already have a good momentum going above 40mph, the ICE is likely to shut down more often (vs 30mph) and let the momentum be handled by the traction battery. Thus, you're able to glide a longer distance coming from a higher speed. That's why you're seeing better mpg at higher speeds in your 8-mile commute. I guess you've nailed the ideal technique and speed for your particular commute.

 

Lucky... my first 3 miles is all uphill. It's great coming home though.

 

Similar here, the engine warm up only takes a mile or so. I usually display around 50 mpg on my 6 mile trip to work, which is the more uphill route, I do much better on the return trip, occasionally topping it out at 99.9.

Make sure to use the ICE during the warm up cycle, that way you aren't wasting too much of that excess power.

 

Now there's a term you never hear on a hybrid forum Especially in the C section

 

Heh yeah, but if you aren't using the power then it become excess power. With the ICE revving itself to warm up it's generating power that could be used to propel the car forward, and is also generating electrical energy that can be stored into the battery. So one should be using those RPMs to drive somewhere to prevent waste, and having some room left over in the battery will help catch even more power before it's lost.

If, while the ICE is warming up, you aren't moving the car, and the battery is not be able to accept any more ICE power input (6 bars), then you're doubly losing out on power that your car is being forced to generate...in other words, your gas mileage will be not be as good as a driver who is able to make full use of the power being generated.

 

actually, during warm up (stage1), the ICE only does just that (warm up). it only does a little bit of generation. at least 95% of that power to move forward comes from the traction battery. it's only when you reach stage 2 that normal ICE operation will start. so it's really better to just stay put for less than a minute for it to warm up properly. it's not bad if you start from a hill going down, but really bad when your going uphill like in my case. do read up on the prius stage operation for more info. : )

 

It acts this way if you have high HV/traction battery power and don't demand much from the engine. If you demand more and there isn't battery power there to handle it then clearly the ICE reacts differently. From my experience it seems to go to normal, or close to normal, output.

I did find this in one of the Prius warm up stage threads to back up what I've noticed:

S1a is Stage 1 A, which is the initial warm up stage we are talking about, clearly the engine is able to provide normal power and charge the battery in this stage under the right circumstances. I'm not usually causing this effect from heavy acceleration, but rather from lack of battery power. I'm glad you brought this up, because normal S1a behavior has confused me a couple of times, being very different from my more common apparently abnormal S1a behavior.

Clearly the vehicle can react very differently depending on the circumstances. Understanding what it is doing helps to know how to act and react.

 

Interesting! Thanks for bringing that up. I'm curious to try it but afraid of any increase in wear and tear of gunning it right away.

 

I assume in more cold weather you'll want some warm up before asking much from the engine, lubricants tend to not work quite as well at low temperatures. I'm not sure what the ramifications are of asking for moderate RPMs from the ICE before warm up is complete in the middle of summer. I'm not gunning it, usually I try stay around 25% into the ICE range of the HSI, except when more is needed for merging or similar. During a regular warm up cycle the C is capable of handling that power request purely with EV propulsion, but only if there is enough of a charge on the battery. Without a decent charge on the battery the vehicle seems to go almost straight to normal ICE functionality, with stealth EV not being available until the warm up cycle is complete.

Reiterating some of that for my own good as well. I'm also a learner here.

 

I also find that driving too long at speeds under 40 MPH results in worse MPG than driving at faster speeds. I think it is because the HV battery gets drained and has to be recharged by the ICE, so gas mileage suffers because of it. I've found the best mileage for me occurs if I drive at speeds closer to 45-60 MPH and average between 60-70 MPG. At 65+ MPH, gas mileage drops to around 55 MPG and lower. I wonder if P&G would help in those low speed routes so that the HV battery doesn't get drained as much...I tend to use CC to hold my speed constant (I know this is bad when traversing hills and such, but I would rather hold a steady speed and sacrifice a few MPG's than piss off people behind me).

 

P&G is most effective at the lower speeds, where wind resistance is less of an issue. In very low speed limit areas I use P&G while staying in stealth EV mode, the reduced drain on the battery and increased total distance on battery alone is immediately noticeable. In 35 mph speed limit areas P&G is also very effective, using slow ICE acceleration up around 40 mph and then gliding until you feel the need to accelerate again, usually in the 20-25 mph range, traffic permitting of course. With no traffic (lone stretch of road in the dead of night) I'll sometimes glide down to under 10 mph, the mpg gain is significant, but at some point you feel like you could just get out and push your car faster than it's going.