So, How Fuel Efficient is This TSX? Test Results & Data *Long Read*

[sauceman]

As mentionned in a thread about a month and half ago, I took a day off during my business trip in Northern Quebec to test away at different fuel ratings and speeds to see what was the optimal way of attaining the best fuel economy. I've tried to be as precise and meticulous as possible with the details and will try to do so in my analysis as well. I was expecting the optimal speed for best mileage to be around 80kph (50mph), to attain a best mpg at around 40mpg US and probably be able to demonstrate that there was no difference in mileage between 87 and 91 octane. Well, as you will see in my results, I was in for a few surprises. I can truely say I have learned a few things along the way as well. What may seem like a patience trial (and maybe was to some point) was in fact pretty interesting for an experiment. I drove to places I had never been before, and that alone was enough for me to make things interesting. Preparation for the Test Recap: The test consisted of 4 cans of 20 litres of gas: 3 of 91 octane, and 1 of 87 octane. The 87 octane was to be driven at 90 kph, and the three 91 octanes were to be driven at 80, 90 and 100kph. I had also brought along an extra gallon of gas to make it back home after the test. The tire pressures were adjusted at 38PSI cold for the rears, and 36PSI cold for the fronts. During June 28th, the day before the test, I also drove in order to be as efficient on gas as possible. This was in order to let the ECU learn to use the leanest fuel maps as possible. Just like when I go to the drag strips, I make sure to do a series of WOT runs to let the ECU adopt a more aggressive fuel map. This is because of the ECU's constant data accumulation capacity. Testing When I left home at 4:20 AM, it was cloudy and foggy with a slight haze. Not looking good, except in my natal region that could well mean it was going to be the weather conditions I was exactly hoping for. It was, however, pretty cool: 13°C. Sure enough, at 7:30AM the clouds all disappeared, leaving myself alone with the sun and the cool temperatures, result of the previous day's heavy, hot and humid weather being pushed away by a cold front accompanied with thunderstorms and showers. Clean and dry air then. So I started the test just after the last traffic light in Amos, Qc. I had to wait until the car sputtered out before I poured in my first 20L to be able to take accurate measures. I would drive until the car sputtered out. And so on for all of the 4 phases of testing. Phase #1: 87 octane at 90kph This test was penalized by 2 factors: slight front wind, and the coldest tempratures of the day. Also, there were more hillclimbs and descents than during phases #2 and 3. I would like to point out that at a constant 90kph cruise, I could not feel the effects of ignition being retarded due to pinging. I did, however feel the car somewhat more lazy during a climb or two. I had to slow down twice: once for a moose, and another time for a check-in gate after Matagami. (see thread about trip and pictures in Photo Gallery, coming up soon) Otherwise, in constant conditions with the rest of the day's conditions, I could add maybe 2 mpg by being generous. Result: 323.7km (201.1 miles). Good for 45.7mpg imp. (38.1 mpg US) Phase #2: 91 octane at 80kph This phase was also penalised by two factors: Rising headwinds really hindered my ability to coast down slopes in neutral. Also, the weather was comparatively cooler than during phase #3. What really surprised me during this phase was the ability to just coast down in neutral (when the wind was low) on ridiculously minor grades. On just about any slopes I could slap it in neutral and let it roll while remaining at 80kph or even gaining momentum. It seems as though the wind resistance factor dramatically diminishes below 90kph. If only the headwind wasn't so strong, I would have been able to add easily another 1-2 mpg there again. Otherwise, no slowing down anywhere, the road was absolutely trafficless. Result: 355.5km (220.9 miles). Good for 50.2mpg imp. (41.8 mpg US) Phase #3: 91 octane at 90kph This phase was advantaged by comparison to the first two phases. Having burned two of my four cans, it was time to turn around, and so the wind had become a tailwind of 30kph decreasing to 10kph. Also, being at the height of the day, I was benefitting from the warmest temperatures at around 21°C. I could coast down slopes a lot easier now and took full advantage of it on my way to my best mpg of the day (and ever, might I add). If the wind was down, I would have had to subtract about 1 mpg (my estimate). Result: 364.0km (226.2 miles). Good for an amazing 51.4 mpg imp. (42.8 mpg US) Phase #4: 91 octane at 100kph As a consequence of my unexpected success at 90kph, I ended up covering more distance during phases 3 and 4 than during 1 and 2. Which means I drove back into Amos, though 3 traffic lights and 2 roundabouts, and obviously at lower speeds than expected. The temperature was also down and back into a hillier region, so these factors somewhat hindered the mpg results. It may be somewhat irrelevant though, as it was clear that 100kph would be far from leading to the best mpg. Still, for comparison, the numbers are worthy, so I gave it my best then too. I think backwind cancelled the cooler temperature factor, so crossing Amos would have penalised me by only a fraction of an mpg, so this phase seems reasonnably representative. Result: 329.1km (204.5miles). Good for 46.5 mpg imp. (38.7 mpg US) Data Analysis 87 Octane vs 91 Octane Who wins? When comparing both phases (#1 and #3, both at 90kph), if we take into account penalizing and helping factors, I would estimate that there would be a discrepancy of at least 3 mpg, and I believe I'm being generous here. This means that 91 octane gas would normally lead to a 6% better fuel economy. On a 60 litres fill at 99.9/L, this means $3.60. So, in Canada, if you fill in gas stations where it costs you 6 cents more per litre for premium (Ultramar, CTC), you have an exact tradeoff, as regular would cost you $56.34 for regular (at 93.9) and 59.94 for premium at 99.9. Optimal speed for optimal gas mileage Well, the wind factor is the main wild card here during my tests. But if you brought down the wind conditions to 0, my estimate is that 90kph would have yielded an inferior gas mileage of close to approximately 1 and half mpg compared to 80 kph. Saintor mentionned in that other thread that Transport Canada was turning the best mpgs at an average speed of 77kph, and I would tend to think this is spot on for the TSX. That would mean an optimal rpm of 2000. I am not sure if the numbers would reveal so favorable for an AT though. I have the feeling at that speed (75-80kph), the AT would be constantly moving the torque lock-up on and off, and even downshifting frequently to 4th going uphill. Km/Litre I added this calculation to give an idea of how far the TSX could travel at those kinds of mileages with any given volume of gas. I use this calculation very often when travelling, and it helps me from getting into trouble, as well as plan my gas purchases in order to find the best prices. Distance travelled with gas light on I was amazed. The variations in distance is very constant with the mileages. This means that the fuel gauge is VERY precise. By doing the math, you can see how much gas was left in the tank during each phase when the light came on: Phase 1: 14.7 litres Phase 2: 14.3 litres Phase 3: 13.9 litres Phase 4: 14.6 litres The variation is of 8/10ths of a litre. Pretty good. Tire PSI Well it seems as though upping the PSI can do nothing but good if you want to get good mileages. But that was to be expected. I was surprised at how little variation in PSI there was from cold conditions to full running temperatures: Only 2 PSI both front and rear. Also, the rear tires seemed to move into temperature quicker than the fronts. I'm curious to know whether this could be linked somehow with the way the back brake pads wear slightly faster than the front pads... Effects of air temperature It was pretty obvious that, the warmer the air, the easier the TSX could take advantage of slopes to coast down on longer distances. I could also compare it to the previous day when, alhough very humid, the air was 10°C warmer, and the car would roll forever in neutral too. Wind resistance at 80 kph vs 90kph If it is true that the engine revs 250rpms less at 80kph than at 90 and that it has a beneficial influence, it is equally as true that the wind resistance is dramatically decreased, and really helps with the mileage too. What is the ratio of each factor in the equation, I really don't know. But my butt guess would be 60% of the improvement attributable to decreased wind resistance compared to 40% for the decreased rpms. Conclusions I've reached 51.4 mpg imperial, or 42.8 mpg US. Still, these numbers were not under the most ideal conditions, but close. So you guys know the TSX 6MT can do at least that much. We also now know that the TSX is most fuel efficient with 91 octane. Now whether the gain in economy offsets the price depends on your local gas station.

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[Dan Martin]

Wow great writeup Jeff!

I'm also very impressed with the results.

[Dan Martin]

I'd also like to add that you have the neatest handwriting of any male I've ever seen.

[Belzebutt]

Originally Posted by Dan Martin

I'd also like to add that you have the neatest handwriting of any male I've ever seen.

Maybe he got his wife to fill out the paperwork.

Great report! I'd love to have the stamina to be able to drive like that... The best city milage I got so far was about 25 mpg US, but I think I must have been super-careful.

[SSN_FT1(SS/DV)]

That is just outstanding work! Good job man

[sauceman]

Thanks guys! Yes, that was my own handwriting. I tried to be neat to be readable, heh.

[Dan Martin]

I once had someone mistake my "7" for a "P" so I'm jealous.

[mg7726]

nice write up!!

REP POINTS!! (Oops, we don't have any)

[ostrich]

Wow! Jeff, I just simply could not believe that you went through all that trouble to get the results - thank you! That was just amazing!!!

I have a 2004 5AT. During summer, I consistently get about 28mph with mixed local/freeway driving (about 50/50 but usually only for about 10-15 miles each trip, even for freeway). I get about 24-26 during winter. If it's all freeway, I get way more than 30mpg!!! I am pretty happy about this car's fuel economy!

[curls]

I find highway mileage a LOT better than city, although I tend to have a heavy foot around town off of stop lights and signs...

But WOW, great write-up! And I assume by "doing the math" you mean that there is an average of 6 liters LEFT IN THE TANK when the light comes on?

Thanks for the wonderful information. Now go change your sig!

~Eric

[Tsx536]

Awesome writeup Sauceman

Thanks for talking the time and effort to perform the tests and also for writing everything up so meticulously!

Can I get a

[sauceman]

Originally Posted by curls

I find highway mileage a LOT better than city, although I tend to have a heavy foot around town off of stop lights and signs...

But WOW, great write-up! And I assume by "doing the math" you mean that there is an average of 6 liters LEFT IN THE TANK when the light comes on?

Thanks for the wonderful information. Now go change your sig!

~Eric

Right, I forgot about that!

When the light came on, I actually had 14ish litres left in the tank. I actually drove the majorit of my testing with the fuel light on.

Thanks again guys.

[curls]

Originally Posted by sauceman

Right, I forgot about that!

When the light came on, I actually had 14ish litres left in the tank. I actually drove the majorit of my testing with the fuel light on.

Thanks again guys.

HOOOOOOLY CRAP!! That rocks! 14 Liter reserve is at LEAST 140km... 200 if I baby it.

Insane!

~Eric

[kyotousa]

No one drive that slow in states.....=_=||
90kph is like 50mph rite XD ahha

[Alin10123]

Sauce, thanks for taking the time to experiment for us!

[BlackAc036]

Once again, very impressive stuff sauce, you never cease to amaze me!

[TSX Cman]

That was a great writeup. Sometimes i got single gastanks of 91 octane and only get as many kilometers as you did with the highest rated test subject (20 L of it vs a whole tank).

nice efficient drivin

[yfin]

The most well written post I have seen in a very long time.

[GreenMonster]

Nice... 42.8 miles per gallons sounds great !!

[dom]

At the effort, time taken and the results.

[joerockt]

Very impressive...Good job Sauce!

Man, I need to learn to stop flooring it everywhere I go

[CGTSX2004]

Wow! Nice work, Jeff. I gotta figure out how you're driving to get these numbers. I don't think I've even come close to numbers that good yet...

[youngTL]

Thanks for the write up. It's great to finally have the most scientific amateur test (although can you even be called amateur anymore ) out there. I hope this puts all those 87 octane people to rest. As the price of gas increases, the relative cost for 91 decreases.

[sauceman]

Originally Posted by youngTL

As the price of gas increases, the relative cost for 91 decreases.

[Superb0o]

I don't know if you've seen Mythbusters on the Discovery channel... But I remember a somewhat recent episode where they wanted to find out if A/C would do anything to MPG. They used appoximitely 5 gallons of gas with the same SUVs (which were both Explorers) and they were both to weigh the exact same including food and body weight. They then drove the cars around an oval track untill they run out of gas at the same speed... One car had the AC on with the windows rolled up. The other had the AC off with the windows rolled down and both had radios going. It turned out that after the first car stopped, (the car with the AC on) the car without the AC lasted 85 laps (i think around there) more. Unfortunately... I forgot how many miles 85 laps actually is... But still an amazing fact.

[sauceman]

Originally Posted by Superb0o

I don't know if you've seen Mythbusters on the Discovery channel... But I remember a somewhat recent episode where they wanted to find out if A/C would do anything to MPG. They used appoximitely 5 gallons of gas with the same SUVs (which were both Explorers) and they were both to weigh the exact same including food and body weight. They then drove the cars around an oval track untill they run out of gas at the same speed... One car had the AC on with the windows rolled up. The other had the AC off with the windows rolled down and both had radios going. It turned out that after the first car stopped, (the car with the AC on) the car without the AC lasted 85 laps (i think around there) more. Unfortunately... I forgot how many miles 85 laps actually is... But still an amazing fact.

Interesting! I thought both would cancel each other out...

[vwong]

Damn, sauceman. That was very impressive. Great writeup.

Can I point out one more thing that you missed in your writeup? Weight. I don't know if you added any weight back when you did the Phases #2 to #4, because the weight also plays a role in gas mileage. When you were in Phase #1, you had 3 20-liters (excluding the extra gallon) of gas in the trunk. If you didn't add any weight back, during your Phase #2, you only had 2 20-liters of gas; and Phase #3, you had 1; and so on. Since 20-liters of gas weighs roughly 13.6kg (30 lbs), the weight of your car during Phase #4 was 40.8kg (90 lbs) lighter than Phase #1.

Anyway, just my .

[psteng19]

Not to doubt you but 40+ US mpg sounds TOO good to be true, even if it's all highway in ideal conditions.
That's near hybrid (Prius) gas mileage.

Also, I've read that if you coast in gear, the engine actually consumes NO fuel at all (downhill/gravity and inertia keep the wheels turning which then turns the crank).
Putting it in neutral will cause some fuel to be injected to keep the engine turning,

So you could've had better results by not coasting in neutral.
The flip side is that you can coast farther in neutral than you can in gear, so...

All in all, good test but there are too many uncontrollable factors (temperature, hills, weight) to make it 100% accurate.

[psteng19]

Originally Posted by Superb0o

I don't know if you've seen Mythbusters on the Discovery channel... But I remember a somewhat recent episode where they wanted to find out if A/C would do anything to MPG. They used appoximitely 5 gallons of gas with the same SUVs (which were both Explorers) and they were both to weigh the exact same including food and body weight. They then drove the cars around an oval track untill they run out of gas at the same speed... One car had the AC on with the windows rolled up. The other had the AC off with the windows rolled down and both had radios going. It turned out that after the first car stopped, (the car with the AC on) the car without the AC lasted 85 laps (i think around there) more. Unfortunately... I forgot how many miles 85 laps actually is... But still an amazing fact.

No 2 cars are created equal. Even within the same make/model there will be slight differences.
Did they re-test the Explorer's but reverse the roles (i.e. car with windows down uses AC and vice versa)?

[Dan Martin]

Originally Posted by psteng19

Not to doubt you but 40+ US mpg sounds TOO good to be true, even if it's all highway in ideal conditions.
That's near hybrid (Prius) gas mileage.

Also, I've read that if you coast in gear, the engine actually consumes NO fuel at all (downhill/gravity and inertia keep the wheels turning which then turns the crank).
Putting it in neutral will cause some fuel to be injected to keep the engine turning,

So you could've had better results by not coasting in neutral.
The flip side is that you can coast farther in neutral than you can in gear, so...

All in all, good test but there are too many uncontrollable factors (temperature, hills, weight) to make it 100% accurate.

Sauceman has achieved similar results before. Even I have achieved high 30's without really trying.

[Motohip]

Originally Posted by Belzebutt

I'd love to have the stamina to be able to drive like that...

If you don't have enough stamina to write nicely, then I feel sorry for your wife or girlfriend.

[sauceman]

Originally Posted by vwong

Damn, sauceman. That was very impressive. Great writeup.

Can I point out one more thing that you missed in your writeup? Weight. I don't know if you added any weight back when you did the Phases #2 to #4, because the weight also plays a role in gas mileage. When you were in Phase #1, you had 3 20-liters (excluding the extra gallon) of gas in the trunk. If you didn't add any weight back, during your Phase #2, you only had 2 20-liters of gas; and Phase #3, you had 1; and so on. Since 20-liters of gas weighs roughly 13.6kg (30 lbs), the weight of your car during Phase #4 was 40.8kg (90 lbs) lighter than Phase #1.

Anyway, just my .

Good point vwong. I forgot to point that out. Since I was in a remote area, there really was no way for me to compensate for the weight unless I added rocks along the way, but that would have been pretty inaccurate as well. So you're right it might throw the numbers off a little. But not to a great extent.

For gas mileage performance, weight is only a minor factor compared to the car's Cd and the speed. Reason why: Although it will require more energy to move an added mass up a hill, what goes up must come back down, and so you can recuperate much of that momentum coasting back down. The heavier the car is, the longer it will stay at speed.

Still though, weight compensation would have shown in my numbers.

This brings out another point I forgot to mention: Weight distribution: I didn't leave all those cans in the trunk during the test. They were all on the floor in the cabin. 1 up front on the passenger floor, and the three others behind the two front seats. The first can to be emptied right at the start was the one sitting directly behind me. Then the center back, then the passenger back, then finally the front passenger can.

This was for one good reason. A good weight distribution will help ensure that you disturb the car's aerodynamics as little as possible. If all the cans had remained in the trunk, the front end would have swallowed more air by the car's undercarriage, not as smoothly profiled as the rest of the body. It would also have diminished the rear difuser's benefits.

I will need to add these two principles to my fuel economy thread (weight distribution and wind resistance vs speed). I believe I had overlooked these factors back then.

[sauceman]

Originally Posted by psteng19

Not to doubt you but 40+ US mpg sounds TOO good to be true, even if it's all highway in ideal conditions.

I didn't expect to get any better than 40mpg either, but I was in for a good surprise.

Also realise that James Bay isn't remotely what Arizona can be. If I had the chance (or maybe the curse because of the heat) to do this same test in AZ, I wouldn't be surprised now to have been able to even reach 45mpg.

[Arcticcl9]

Great writeup, sauce!

like someone else mention, we do not go 80km/h here in the states...we go 80mph regularly on the freeways! But interesting to see what the TSX is capable of, doing 40+mpg.

[Belzebutt]

Originally Posted by Motohip

If you don't have enough stamina to write nicely, then I feel sorry for your wife or girlfriend.

I said drive like that, not write like that.

And yes, it's easier for me to have patience doing that than while driving behind an old fart blocking the left lane.

[TinkyWinky]

Wow! Great report man.

A little comment, if I may.

As you mentioned in your reply to VWONG, constant highway driving should not significantly affect mpg. However, if you used cruise control, you would not actually be getting back lost energy (e.g., on downhills) as the engine brake would be used to maintain a constant speed.

Maybe next time you could fold the side mirrors to see if they make any difference.

[Dan Martin]

Originally Posted by TinkyWinky

Wow! Great report man.

A little comment, if I may.

As you mentioned in your reply to VWONG, constant highway driving should not significantly affect mpg. However, if you used cruise control, you would not actually be getting back lost energy (e.g., on downhills) as the engine brake would be used to maintain a constant speed.

Maybe next time you could fold the side mirrors to see if they make any difference.

Engine braking doesn't give you any extra energy. We don't drive hybrids.

[TinkyWinky]

Originally Posted by Dan Martin

Engine braking doesn't give you any extra energy. We don't drive hybrids.

[sauceman]

Originally Posted by TinkyWinky

Wow! Great report man.

A little comment, if I may.

As you mentioned in your reply to VWONG, constant highway driving should not significantly affect mpg. However, if you used cruise control, you would not actually be getting back lost energy (e.g., on downhills) as the engine brake would be used to maintain a constant speed.

Maybe next time you could fold the side mirrors to see if they make any difference.

I was using inertia by coasting down the hills in neutral. No engine braking at any time.

[TinkyWinky]

Originally Posted by sauceman

I was using inertia by coasting down the hills in neutral. No engine braking at any time.

6MT >> *