Prius Hates Being Below Sea Level ! (Extreme Prius Driving Part 2)

i've never taken the pri to fl, but have been there many times in our hycam. mpg's never changed from virginia to fort myers and back. 40-45 all the way.

 

If you are going to repeat it, I'd also suggest trying it in cooler conditions. The heat triggering some sort of battery protection would seem like a much more likely cause of low mpg than would low altitude.

 

If you get a chance to repeat the test:

• run 10 mile segments at different speeds - this will give a clue as to whether it is overhead, rolling, or aerodynamic
• make sure you have a reference to compare

Now in a perfect world, you would have an OBD recording system to measure ICE rpm, mass-air flow, MG1 torque and other metrics. We do not have enough information to tell if is engine, transaxle, tire, or other.

Bob Wilson

 

Just a minor technical point about the "10 mile" segments. I've found over the years that the indicated MPG achieves a steady-state over the same route, direction, and temperature. Anything less and there can be too much variability. Longer is better but I don't have the time to waste.

Also, the reason for different speeds, especially if we can get two extremes:

• high-speed - predominated by aerodynamic drag, the rolling resistance remains constant
• low-speed - predominated by rolling resistance with less aerodynamic drag

We know the drag force is proportional to (from memory so I may get some wrong)

1. drag ~= air_density * cross_section * coefficient_of_drag * (velocity ** 2)
2. rolling drag ~= coefficient_of_friction * weight
3. transmission loss ~= constant_per_transmission * viscosity * velocity

In the past, many used just the first two terms. However, the EPA/DOE uses the three parameter formula. Regardless, the old-school, two term is good enough. Two data points are generally enough, if accurate, to derives the coefficients for the two parameter formula. But usually an instrumented roll-down test is used (which can be done using a recording GPS such as a Garmin) because it gives data points for the car drag without the engine. . . . now I'm techno-babbling.

What ever data you can provide will be appreciated and give insights as to what is going on. The more data, the better, but we'll survive. <grins>

Bob Wilson

 

If you have a GPS or topo map available, please note the elevation of the start and end points of each measured segment, not just the average or typical elevation along each segment. Prius mpg is very sensitive to even small climbs or descents, so we will need to make some adjustments.

 

Strange, nobody ever mentioned using the AC ?