Understanding the mileage in my commute

Thanks! By accident I reset my odometer after warmup had occured, and my mileage for the day was noticeably higher than normal. So now I've started doing some experiments, but none as elaborate as yours. Very interesting, and it may have some bearing when people talk about their terrible mileage.

I'm interested in what will happen in the winter. We park in an underground garage, so the ambient temperature is always 50 degrees F, or higher, so it'll be interesting to see if that helps in the winter. The two variables, in my mind, would be: 1) that will make the car 20-30 degrees warmer than outside temperatures, but obviously the engine needs to warm up way more than that anyhow, and 2) what happens when I exit the garage and hit the cold outside air?

 

Excellent!

I have another set of instrumentation so in my NHW11 (2003 Prius,) I can record the data in a laptop. So I was wondering if you used an audio recorder, voice recorder or other means? Does your route include speed changes, stops and altitude changes? Temperatures? Were these from several runs averaged together? Average speed?

When the local temperature are in the middle 80s, I typically see ~52 MPG on the route to work and ~60 MPG on the route to home. But my route includes speed changes, stops and an altitude change.

As a tip on how to do tables:

• use "table" between "[" and "]"
• use "|" on the first row to separate column headers
• use "|" between each data item on each row
• use "/table" between the "[" and "]" to end the table

I often cut-and-paste spreadsheet data into a text editor and then replace the <TAB> with "|". Then I insert the "TABLE" and "/TABLE" tags at the front and back. Finally, I paste it into the web entry text area.

BTW, this is the type of data recording criticial to mastering our rides. My curiosity about your technique is to help everyone understand how easy it is to record useful, detailed data. Well done!

Thanks,
Bob Wilson

 

All cars suffer a fuel economy hit from frequent short trips. All is relative.

 

Time for an engine block heater.

Wayne

 

Do you have a ScanGage to record fuel used?

Wayne

 

At 30 mph, use the EPA Jetta TDI City and 2010 Prius City mileage numbers. You will find the Prius beats the TDI and your own data shows that after warm-up, the Prius gives excellent mileage. But there is another way to understand why the Jetta TDI in City mileage has relatively poor performance:

• engine running cars - a TDI will keep the engine running all of the time. It does this to keep the accessories working including power steering and brakes. During this time, the engine has to overcome its own internal friction, the minimum amount of energy that has to be consumed to turn over the engine. This is about the same amount of energy as the starter uses.
• engine off/on hybrid cars - the Toyota, Ford and to a lessor extent, Honda, hybrids all turn off the engine every chance they get. This means the engine 'keep idle' energy is not spent.
• at 30 mph - the power needed to keep a vehicle rolling is about 5 hp, about the size of the TDI starter, about the amount of energy needed just to keep it idling. The Prius has the same 5 hp requirement to sustain 30 mph BUT the Prius turns off the engine every chance it gets. When it does run the engine, it runs it at a high enough power level so the engine overhead is a fraction of the fuel burn. This is why it works so well.

One of these days I may get a chance to rent a Jetta TDI and if I do, I'll take time to plot the MPG vs MPH so we can compare it to the 2010 Prius.

Bob Wilson

 

Right, all ICEs are least efficient when they are cold. I believe we will take a double hit in the winter because I believe the traction battery will not be as efficient when cold either. But we will just have to see. In the end, we still will likely get better mileage than in our previous cars.

Peter

 

Japanese folks are seeing huge mileage improvement using the EBH even in 95F summer.

Ken@Japan

 

Makes sense: I believe that the engine runs until the coolant is about 150 degrees F, so even at 95F, you've got another 60F of warmup to go.

 

Yup! I use mine every single day, 365 days a week!

About 3 hours pre-warming on my 2G having a garage temperature of about 21ºC is enough to prevent the ICE from starting up to run the warm up sequence.

 

I don't know about the Jetta's technology, but I know that diesel trucks take a considerably longer time to warm up than do the gasoline versions. Does the Jetta have a coolant heating system by the exhaust like the 2010 Prius does? If not, this could also negatively affect the short trip efficiency of the Jetta in cooler weather.

 

The Jetta has an EGR cooler which sucks some heat from that stream. But it will still take it longer to warm up than the Prius, because of the Prius' dedicated exhaust coolant heater and the naturally efficient diesel combustion. For anyone looking for a vehicle for 1-2 mile trips, my recommendation is a bicycle or some comfortable shoes. The TDI and the Prius will both guzzle for short trips from cold starts.

I can't speak much for the 2009 TDI, but from reading online, I find with my 2001 that I can do a little better in short city trips from a cold start than a 2G Prius in the same situation. Both cars are sucking fuel down at an alarming rate, but I may do slightly better because the Prius is also restricted from doing some of its magic until it warms up.

 

How much power does the EBH draw?