Cruise Control MPG at 31 MPH - bwilson4web
 

Bob,

As a disbeleiver, I went out the other day and set the cruise control to 31 MPH and sat back to watch the fun on the consumption screen. I was not able to acheive an average of 90-95 mpg as your speed vs. mph chart shows (I have seen it in your responses to others who post good FE numbers using the P&G technique). I had to try it, becuase life would be a lot easier by just setting the cruise control and watching the world go by rather than concentrating on P&G techniques.

I had two 5 minutes segments in the 60ish mpg range. I was on mostly flat roads (<20 feet elevation change), no traffic, light winds, 70F, no AC, windows up, 50/48 psi, full conventional oil, etc. Any thoughts? I believe I have 6 bars of SOC. I have about 2300 miles on the car. Could it be that I needed a higher SOC?

Thanks,

Chris

However, I have been P&Ging like a fool. I am at 601 miles at 74.4 MPG so far this tank. Maybe 900 miles is in the future. It will be very close. I may have to wait until next year for warmer weather.

Re: Cruise Control MPG at 31 MPH - bwilson4web
 

Excellent! This is how we find out what works and doesn't work by having independent replication of results and when there is a difference, understand what happened.

The only differences:

1) methodology - upon reaching 30 mph and setting the cruise control, I reset the MFD. The mileage was recorded from the MFD calculated display at the end of each 2.5 mile run. I made sure it did not include the accelleration or decelleration to 30 mph but covered ONLY the steady-state mileage.

I don't use the 'mileage bars' since on my NHW11, I have to turn off the vehicle to reset them. Worse, they don't give exact mileage to the nearest 10th of mile per gallon like the calcualted MPG value at the bottom.

2) oil - I run at 3/4ths of full, using Mobil 1. When I returned from Texas, it was one of the earliest modifications, to reduce an overfilled tank to 3/4ths, and it had a measurable impact.

3) fully warmed up - an oil pan temperature probe confirmed that the transaxle oil in my NHW11 is not fully warmed up until at least 30 minutes at speed. Since all power, including the EV mode, has to flow from and through the transaxle, it is important to make sure this part is also at operating temperature.

To minimize the effect of SOC, I put the car in "neutral" at the end of each run and used mechanical braking to stop for the turn around. This avoided any regeneration effects. Also, I mixed up the different speeds for each run.

Of all of these effect, the methodology, using the MFD calculated display value, is the one that I suspect will have the greatest effect. If you have occasion to repeat the test, do follow this approach:

1) fully warmed up - at least 20-30 minutes of normal driving
2) set cruise control at target speed
3) reset MFD mileage and one of the trip meters
4) at end, quickly note the trip meter miles and MFD mileage

My test runs were over a 2.5 mile, flat section, sheltered from a cross-wind by trees on both sides.

BTW, I recently got one of Graham's OBD mini-scanners. Last night, I was able to work up the fuel consumption as a function of injector timing. Later this evening, I'll find some recorded segments at 30 mph to calculate the mileage at this speed using injector timing. The big advantage is I'll be able to document the EV vs. ICE assisted durations.

Bob Wilson

Re: Cruise Control MPG at 31 MPH - bwilson4web
 

Thank you for your response. From the last few months (since I joined), it is clear who is taking the majority of data around here. Thank you for your efforts.

I have decided to change to Mobil1 0w-20 at 2500 miles so that I can provide a sample to Blackstone Laboratories for baseline data. It seems like a good number. I will resume the 5000, 10000, 15000 mile oil change intervals after that. The dealer will change the oil for free as long as I take it to them (part of the deal for buying a car there).

What safety factor do you think tire manufactures place on their max sidewall pressure? 1.5? 2?

Weather has turned colder, 45F instead of 65F in the mornings. This is my first winter with the car and temperature is having it hand reducing my FE; I was only able to get about 68 mpg on the way to work instead of about 80 mpg. :D

I am very hung up on keeping the mfd numbers as well as the calculated numbers for my records. I think I might have a heart attack if I reset the MFD midtank. Silly how this matters to me. When I find a more isolated area, I will attempt another run with a fully warmed car in warmer weather at least 70F; as that is what I believe where your data was taken. I might be able to give you crude feedback when it gets warmer next week.

Thanks,

Chris

Re: Cruise Control MPG at 31 MPH - bwilson4web
 

Hi Chris,

Actually, I'm just following the same footpaths laid down by the YahooGroup, "Prius_technical_stuff." I'm just a student to the wealth of information and technical papers published over the years.

Sounds like a good plan. I've bought some Fumoto valves to make it easier to take samples without having to change the whole tank. Right now, I'm waiting to get 15,000 miles on my current transaxle oil before the making the changes.

I don't worry about it. I've got my cold pressure set to the max, 51 psi, with 50 psi pressure sensor caps on all four tires.

I earned my hypermiler star the end of January of this year. You can exceed EPA numbers even in the cold. BTW, I have an experiment going on to look at warm-up strategies and will be adding block and transaxle pan heaters on the next change.

No problem. I had bought a used 03 Prius with 49,300 miles on the odometer so I soon adopted the following:

1) calculate MPG for database - I use the gas recepts and a trip meter for the official vehicle mileage.

2) MFD display for tests - when I need to try one approach versus another. It is how I had been measuring warm-up consumption.

Bob Wilson

Re: Cruise Control MPG at 31 MPH - bwilson4web
 

One technique useful if you don't want to reset your MFD is 'differential' measurement:

1) start of test, record tripmeter mileage and MDF MPG display
2) end of test, record new tripmeter mileage and MFD MPG display

Use #1 to calculate the fuel burned pre-test and #2 to calculate the fuel burned post-test. Take the difference, the fuel burned during the test. For mileage, just use the difference in trip meter mileage. Then calculate the MPG for the test interval.

Bob Wilson