MPG Observation

[Richard L]

Good point Yardsale !! LOL



That's what I have been trying to say...too many people have preconceived notions as to what their mileage should be and that tends to creep into their testing.



Much better to go into it with and open mind, with a determination to be as accurate as possible, and knowing that there are variables that you cannot control...like traffic, construction, accidents traffic lights, weather, wind, temperature, etc. All of them can have an impact on your mileage.



....Rich

 

[Peter V]

Yardsale, perhaps I did not clearly explain my original observation. It's not a comparison on city/highway driving affecting MPGs. My observation was about the difference in my MPGs when I had a decent load weight compared to no load whatsoever (19-20 compared to 16-17, respectively).



The observation I made was over a 20-30 mile stretch. Most factors being similar, IE, route, traffic flow, speed, etc. I noticed that when I had several hundred lbs of weight, my ST got higher MPGs compared to when there was no load. This I could not explain.



With today's experiment, I am driving a route of roughly 100+ miles with no load. The return trip on the same route, will have roughly 300-400lbs.

 

[swshawaii]

MPGs calculated using the computer's system. (I know it could be off +/- MPGs)



I plan to "RESET" my MPG calculator once I've passed traffic and will see how my MPGs look for the trek down. Keeping all things as close to constant as possible (IE, speed) on my way up and loaded with 4 rims/tires (I would guess about 300+lbs) I will once again, "RESET" my MPG calculator to see what MPGs I'll average.

Knowing that, what's the point of only using the MPG calculator? Would be interesting also using the proven top off method during the second test, and comparing the two.

 

[Yardsale]

But it is a comparison between city and highway driving and affects of weight. The element of weight is negligible - 100(300/4500)~6%. That's about two additional tanks of fuel. Another consideration is terrain - gross and net elevation gain and loss (this is partly why an out vs back comparison isn't accurate). Let us not neglect head vs tail wind; temperature and humidity (these are also typically negligible).



This is why most here have gravitated toward the driving characteristics as the difference in mileage. The point is that driving characteristics have greater potential to affect mileage than the weight differences proposed (300 to 700 lbs).



You have a single experiment with two variables (weight and driving characteristics) and you will never determine which made the difference without isolating them (two sets of experiments - one for weight difference and one for driving characteristics difference - and compare the percentage difference). If you want a pseudo-scientific experiment, try this:



1) Drive some route, out and back, however you want. This is your "control" experiment.

2) Drive the same route the same way (same driving characteristics) with added weight.

3) Drive the same route (without added weight) like a maniac.



In other terms ...



1) Walk some block, out and back, however you want. This is your "control" experiment.

2) Walk the same block the same way (same walking characteristics) with an added 12 lbs (6% of 200 lbs).

3) Sprint the same block (without added weight) in 10 yard intervals.



"Your mileage may vary."



Out.

 

[Richard L]

zcspec,

To simplify your two scenarios.....they are not the same.



1. Two short trips to work and back of 30 miles each way is not the same as a long trip of 140 miles each way.



Cold engines require more gas. When you start your vehicle cold and drive, you are not getting anywhere near maximum gas mileage until the vehicle warms up. That may take up to 10 miles depending upon the ambient temperature outside, engine load, etc. The longer you drive at a constant speed after the vehicle is warmed up, the better your overall gas mileage will be for that trip....



When you first started your 30 mile trip to work, you may have only only averaged 14-15 MPG for the first 10 miles while the engine warmed up...the remaining 20 miles of your trip you may have gotten about 21-22 miles per gallon, but your overall trip mileage was about 17-18 MPG. The time you drove with your best gas mileage was too short to compensate for the first ten miles of poor gas mileage while the engine was warming up.



When you started on your 140 mile trip, we can assume you got the same 14-15 mpg until the engine warmed up completely. But then you drove the remaining 130 miles getting 22+ miles per gallon. Your average MPG for the whole 140 mile trip was much better because you drove much further while getting the better MPG which averaged out the poor mileage while the engine was warming up. That's why they always say to avoid making short trips (less than 5 miles) because your engine does not get a chance to warm up and you will get terrible gas mileage on a cold engine.



I notice the same thing with my UltraGauge. When I first start to drive the mileage is not that great, but the longer I drive the better the average MPG gets.



My UltraGauge displays water temperature and when the engine is fully warmed up it reads 185 degrees. Until it says 185 degrees I don't get the my best gas mileage.



....Rich

 

[Duane Foster]

Excellent explanation Rich.

 

[Peter V]

Let me first start off by saying, we have some pretty damn smart or logically members here.



My little "experiment" concluded last night and it should not come to a surprise, but pretty much all the feedback I receive was correct. In short, the first leg of my 130+ mile trip down to Portland, OR netted me about 21-22MPGs. The trip back to Seattle with the 4 rims I picked up netted me about 18-19MPGs.



Like what many of you stated, when you first drive your vehicle for a limited amount of miles, MPGs suffer. Once that vehicle gets warmed up to proper homeostasis state, MPGs improve drastically. I was truly impressed with how well the V8 did, consistently into 21's and sometimes 22's. Now I completely understand why a 20-30mile drive is so vastly different than a 140+ mile trek in terms of MPGs.



Thanks for all the input!

 

[Richard L]

zcspec,

I'm glad you understand. and hope that you will pass this on to others....that way everyone learns a little something. :supercool:



...Rich