Getting great gas millage now i cant get above 45 computer

Good deal,

What speed?
Does it include the turnaround?
Temperature at the time?

Bob wilson

 

Did the mileage drop occur about the time the alignment was performed? I wonder if something might have been messed up during/right after the alignment.

There are threads discussing A/C usage. One interesting thing was the use of A/C and controlling the fan and the impact it has on mileage. Long and short, it was determined to be more efficient to use the Auto for A/C. What I typically do is adjust the temperature such that the A/C is blowing 2 - 4 bars. Thus, if my car is very warm (sitting in the sun), I may set the temperature to 82F and the fan will run with 4 bars. When it slows down to 2 bars, I'll drop to 78 - 80F, such that the fan increases to 3 - 4 bars. When it drops, I'll drop the temperature another couple of degrees until I hit a temperature I'm comfortable with.

For what it's worth, your mileage is right near the middle of the bell curve for Prius V.

Toyota Prius v MPG Reports | Fuelly

 

What we need are a series of mph vs MPG data points so we can chart the effect of speed on your mileage:


Our Prius have these drag forces:

• rolling - tends to be constant force regardless of velocity
• stirring - tends to be proportionate to the velocity
• aerodynamic - tends to be proportionate to the square of the velocity

So using cruise control, we like to have at least three different speed points, the average of two passes in opposite directions at a constant speed. Three points are enough to verify your car is performing or not performance per the expected drag curve:

1. 30 mph - cruise control set, two passes, opposite directions
2. 45 mph - cruise control set, two passes, opposite directions
3. 65 mph - ""

Thanks,
Bob Wilson

 

Good luck!

Quantify the Problem

On the way home with the new 2010 Prius, we ran benchmarks to generate this chart:

To get 45 MPG, I would expect your speed to be between 75-80 mph. But apparently your speed varies between 45-50 mph so I'm not really sure how your speed was managed.

Divide the Problem

The car has major subsystems that contribute to fuel efficiency:

• Engine - when in hybrid mode, speed under 42-46 mph, warmed up, does the engine turn itself off? Is the engine running in a fuel-efficient mode when the engine coolant is equal or above 70C?
• Rolling drag - is there evidence that the tires, wheels and/or transmission are running hot?
• Aerodynamic - unless something is hanging down under the car, say one of the panels flopping down to be a parachute, not very likely but it is under the car, a place hard to see. But a missing, underbody panel might have a similar symptom.

To diagnose this problem further requires more detailed observations. Your mph vs MPG chart on 'flat' using cruise control to manage the speed is key to starting to fault-isolate.

Bob Wilson

 

Temperature changed. We have summer now. Drive one day without AC (windows fully open) and report back.

BTW, when my significant others drive my car (AC full blast, mashing gas and brake pedals to the max) they get 40 MPG, I get 60 MPG (indicated, city).

 

OK, I just tried to help, but it seems you know better, so I'll shot up.

 

It is unusual to have your actual mileage be greater than your "displayed" mileage, especially for more than a single tank (where you might get an incomplete fill up). Has your displayed tank mileage been constant, but your hand calculated value decreasing? In other words, you had displayed 45 mpg before and calculated it to be 50 mpg, and now you have 45 mpg displayed and calculating it to be in the low 40's?

 

One of the first things I do with new tires (or Prius,) is measure the error between the indicated speed and miles. What happens is a slightly smaller diameter tire causes the wheels to turn faster so it appears you are going faster and further. A 2 mph difference at 50 mph is a 4% error.

The problem is a faster spinning wheel means a faster spinning transmission, increasing the transaxle drag . . . not good. One of the reasons our 2003 has over-diameter tires is to achieve a 6% decrease in transmission drag. But in your case, the problem is complicated as the indicated MPG is worse. So if your odometer is say 4% off, take the indicated:

MPG * (1.00-0.04) = MPG * .96 ​

Bob Wilson

 

I start with Tire Rack and lookup the tire specs. But after mounting tires, I then confirm what is going on by comparing the indicated to GPS or mile-marker distances.

So if I read this correctly:

41.5 MPG @50 mph :: your metric​

Something is dreadfully wrong. This will take some work but our 2010 is currently in another experiment. Let's go down the list:

1. Are the tires or wheel hubs warm or hot? - From a constant speed, say 50 mph for 5-10 minutes, come to a stop and walk around the car quickly feeling the tread and hub of each wheel. Heat is the signature that something is wrong with a tire or brakes. So we want to eliminate a dragging brake.
2. Engine oil? - Could someone have used something other than a 0W-20 ? A heavier grade oil would make the engine work much, much harder.

Let's survey your Prius instrumentation:

• GPS that records the route (aka., Garmin nuvi but others may too) - a recording GPS can be used for a series 'roll-down' test. Once our 2010 Prius finishes the current marathon drive, I'll do that and post the results.
• Prius-aware scanner - Scangauge II or miniVCI and laptop or AutoEnginuity . . . something that will let us read out what is going on in the engine, transaxle, traction battery, and other loads. Do you have any of these?

Excellent! We'll do a Google Earth analysis and post it later.

Download the KSbench.kmz.txt file and take off the ".txt". Use this file with Google Earth and you'll see the part of the path usable for benchmarking. However, W. 175th (Rt 56) looks to be a better road for benchmarks because of fewer intersection and turns. But you know the traffic better than I do.

Bob Wilson

 

• miniVCI ($40) - XHorse software hacked Techstream but it only runs under Windows
• AutoEnginuity ($500) - unhacked, it also runs only under Windows
• Scangauge II ($150) - various sources

Engine oil - Do you change your own or take it some place? How many miles ago? What does the current oil look like on the dip stick, post a photo? Put a drop on a piece of paper, white coffee filter paper is best, and post a photo after 30 minutes?

Transaxle oil - We recommend it be changed fairly soon with a one cup sample saved in a clean, dry water bottle. It does not have to be analyzed but if not captured, it can never be analyzed. Toyota will change the oil and save a sample, you bring the clean, dry, container, for a reasonable price.

This is why benchmarks are so important, to make reproducible numbers:

• warm the car up - drive for a 3-5 miles just to let the engine reach operating range
• set cruise control to a given speed - 25, 40, 65 mph
• reset a trip meter
• run ~10 miles without stopping or significant speed changes, use cruise control - ensures the MPG has reached a steady value
• read-out the MPG
• turn around and repeat - mostly removes altitude and wind effects
• repeat in opposite direction

This tests everything from the engine through the transmission and tires. But to draw any useful conclusions, we need at least three data points, slow, medium, and highway speeds.

A "roll down" test is shifting from "D" into "N" at a given speed on a flat section and recording the speed as it falls off. This is repeated in opposite directions, three to five times, a total of six to ten passes. The results are averaged to remove uncontrollable variables. The velocity decrease is a function of vehicle drive, the transmission and wheels, so the engine is NOT part of this test.

Roll down tests are used to figure out the drag forces for a quadratic equation (aka., Ax**2 + Bx + C) to determine how close your car is performing to the new values. The EPA has these values on their web page from the vendor.

A Garmin nuvi GPS records these data in an "*.xml" file. A GPS mouse, most are 'bluetooth', can connect to an iPad or iPhone. These also have built-in GPS and you would need a recording app.

We have not identified any failed part so let's not "set our hair on fire" yet. <grins>

Bob Wilson