evolving_machine

I have a new Scion tC 2015, and I have read that others have been experiencing the low gas mileage for the Scion tC, and especially for those that have the manual transmission. I have a few theories as to why that would be and would like to share them.

I was unaware of the difference with the gear ratios of the manual vs. the automatic, as noted below, before I bought the car. The torque converter being less efficient than the clutch I would have to assume that there would be a bigger difference
with the mileage on the two transmissions.
The car seems to be designed to be an aerodynamic drag instead of being slippery in the air. It has that large flat area in the front below the bumper, that Toyota is selling as a means to control the car.

And then I have this idea that I would like to run by others in this forum and I hope it does not sound to radical.

The car has many systems that use the braking system to control traction, cornering,and braking. The quick reference guide says there is a "Star safety system," "Vehicle stability control," "Traction control," "Brake assist," Electronic Brake force distribution,"
and "Anti-lock brake." All are just modifications to the braking system.

The following is what I have been able to figure out, yet I have not read how this is done, so it is pure speculation. If I am driving on a slippery road due to ice, the computer will know that the steering wheel is pointed in a straight line direction,
the computer will sense the speed of the car, and know the rpm of each of wheels. So if the car is pointed straight, and the front left tire is rotating 1.5 times as fast as the other tires the computer will brake the front left tire because it will assume it looses traction due to slip.
How much faster or slower does a wheel have to turn in order for the computer to adjust the wheels? I can only assume that it is not much of a difference between the one wheel and the others.

If I am driving on a bumpy road, and then go over a pot hole or two, one of the wheels will be rotating faster when that wheel is over the hole in the road because it temporarily looses traction.
Will the computer make another assumption and adjustment that wheel by breaking it in order to control traction?

If I am driving over a bridge, and it is a windy day, will the computer adjust the car and brake certain wheels in order to control the car in a condition the computer senses as a cornering issue?

How often do the brakes engage when I am driving because the computer thinks the car needs assistance in controlling the car?

With the four wheel disc brakes, how long after the brakes are engaged will it take before the calipers free up? If the car is constantly applying the breaks will that effect the gas mileage? Will the lower gear ratio effect the gas mileage?
Will the Chicago Cubs ever win the World Series?

If I am correct, then it is all the controls over the braking system, and the gear ratio that is causing the Scion tC to have poor gas mileage. It is either that, or Toyota just wants to sell more Prius' (hehehe).


6-speed manual w/OD

Transmission gear ratio (1st) 3.54 Transmission gear ratio (2nd) 2.05 Transmission gear ratio (3rd) 1.38 Transmission gear ratio (4th) 1.03 Transmission gear ratio (5th) .88 Transmission gear ratio (6th) .73 Transmission gear ratio (reverse) 3.55


6-speed automatic w/OD and auto-manual

Transmission gear ratio (1st) 3.30 Transmission gear ratio (2nd) 1.90 Transmission gear ratio (3rd) 1.42 Transmission gear ratio (4th) 1.00 Transmission gear ratio (5th) .71 Transmission gear ratio (6th) .61 Transmission gear ratio (reverse) 4.15

____

Locke

What exactly are you considering "poor gas mileage?" I don't have a 2015, but I do have a 2013 6 spd Manual and I average 30.9mpg which exceeds the expectations I had when I purchased the car.

evolving_machine

I am traveling from NJ to DC and back twice a month. This is highway miles. The best mileage so far, is 27 mpg.

Locke

That does seem a little low. My daily commute isnt city or highway, more inbetween both and my mpg reading is always 30.6 - 30.9. I also recall seeing someone post a picture on here of them achieving 37 on a 2nd gen.

stenger

Are you running 0w-20 full synthetic oil?
Have you changed the oil yet? (your first few thousand miles may not get the best mpg until the motor has broken in. Typically after 1rst oil change the MPG will improve)
Are your tires properly inflated.
Are you driving with the windows down/roof open?
Are you obese? Or carrying extra weight?
Are you running heavier wheels than factory?
There are a crap ton of variables to consider here.

But the main one is MPG ratings are based on the speed of 55mph. So if you are doing 70-75mph on the interstate (as most at least around me are 70mph limits) you are exceeding the tested limits of MPG rating.

This all being said I still average 28-29mpg city, 30-32mpg hwy. I have under sized tires on MB Battle wheels (weight is a tad less, but RPM is now higher at 70mph). I have a K&N drop in filter. I use 0W-20 Mobile 1 Full Syn oil. I check my PSI every 2 months *unless weather drastically changes*. I use 92/93 pump gas only. And I have a 6spd manual and mine is a 2014. 2014/15 shouldn't have any major changes other than a few lbs in weight from chassis brace improvements.

evolving_machine

The car is a 2015 with less then 1500 miles so far. No modifications, I keep the tires as hard as I can with the pressure, and am trying to drive very conservative.
The windows are shut, will probably never open the moon roof, and other than a GPS, phone, computer, and travel baggage the car is stock.

Well at least, from what I am seeing here, it is unusual. At first I thought this was typical of every tC. I'll wait it out, and hope it improves with age.

___

Xversa

Don't forget, cold weather adversely affects your mileage. I regularly got 30-33 mpg in mixed driving. 37K on the clock.

evolving_machine

Of course, I understand that the engine has to break-in a little. However, it is not like the olden days where you had to do an oil change before the first thousand miles. Although, I want to get what ever gunk is in there out before I reach 5000 miles.

I have heard that many factories also break-in the engines and let them run a bit before they put them in the cars, makes sense, saves a lot of time and money later if there are problems. Now the engines have a higher tolerance between the bearings and the journals. I also read that when they switched from the flat head to the overhead valve heads they saw an increase in horse power, compression, efficiency and gas mileage because carbon built up on the top of the pistons and the bottom of the heads.

Time will tell, I hope it does increase. However, I am still curious if the breaks are engaging as I indicated above, under normal driving on rough roads and windy conditions, or just when the computer senses a situation that it may think is a handling issue.

Red2014tC

My millage did improve slightly after the 10K miles mark, but it is a large 4cyl engine. you are not going to get 40+ mpg out of a 2.5L period. It is listed as 22mpg city/33hwy iirc. pretty much what I expected tbh.

evolving_machine

Thanks, I am looking forward to the 33 Mpg. Right now I am driving around trying to put it into the highest gear possible as soon as I can. Yeah, I realize it is a big 4 cyl. with a 2.5 liter. I had a ford truck with a 2.9 liter V6, and on that truck I was getting about 26 miles per gallon overall.

stenger

I skip first gear ofter. Too short to need it for anything but hill starts.

evolving_machine

hehehe, I had a GTO (Pontiac) many years ago. I used to go from 1st to 4th all the time.
One time the cars clutch linkage broke and I was only able to shift when the engine was shut off,
so for a little while I just started that car in 4th. But, the tC does not have the horse power and torque of a GTO.

I have to try skipping 1st next time.

____

disaster06

Can't trust the computer, it will say one thing and the numbers never are accurate. I usually get about 350 miles to the tank and when I fill up I had about a gallon left, so that means I get about 27.7 mpg + or -.

I have had the occasional where I got 425 miles to the tank, with a gallon left at fill up (about 31.5 mpg) but I can't imagine much more from the car than what your getting now.

Mine is a 2011 stick. I have slightly wider tires, but got the same with the stock tires.

You could always try the new crawford eco block. Thats supposed to lean out the car and improve mileage. I haven't gotten too much more since buying it though.

rnaz1017

I have a 2012 Automatic, I usually always get 28-30MPG in mixed driving. Open highway best i've ever gotten was 32-34 which is pretty good since the car is only rated at 26 combined. Stock tires, only thing I do different is use 94 octane.

Which is alright for this weight, engine, power etc. We won't be able to match the MPG of newer cars with direct injection, on top of that the drag 0.325 is higher than most cars. Guess that flat helmet like roofline really messes up the drag, the price of rear seat headroom.

KKWL

Mines a 2014 tC manual.

When I drove this car it very rarely went on the highways so avg for me was 8.9L/KM but now that I work at a different job I drive a ton on the highway so my avg is now 8.3 L/KM

In terms of fuel usage I generally fill up at half tank or 25% of my tank left.

Tricky85

I've noticed on my 05 tC automatic that when on a slight downhill it activates braking to reduce speeds as to mimic gearing down for a manual and it seems to be burning fuel faster. Avg. 22-24 but also has 160k miles.

___

Chazman

It's definitely not braking downhill, its just natural off-throttle engine braking, which is reducing the fuel being burnt during that state. Much more pronounced than the Corolla I had, and I prefer it stronger.
To chime in on mileage, I'm getting roughly 8L/100km (29mpg) combined in the summer, 9L/100km(26mpg) in the winter (+winter tires). Stock everything with the RS10 body.

__________________

BurgunScion13

My 2013 is averaging just shy of 30 mpg in (mostly) city driving. The previous owner was getting around 25. I used to own a 944 where I learned that the bigger 4 banger has enough torque to allow RPM's to be as low as 1500 on flat ground or minimal grades. It has the torque unlike my previous vehicles with 1.8 and 2.0L where I had to keep at least 2000rpm or it would bog. Of course a downshift is required to accelerate. In my manual Scion TC that means 5th gear at speeds as low as 30mph (50kph). Driving style can make a huge difference.

I live near sea level in a smaller city without many freeways but, thankfully, not as much start/stop traffic and endless lights. When I am driving in busy places like that, the mileage drops to around 28 which, is still great for city driving in a car with a "big" 4 banger. If you want hyper mileage, by a car that is post 2019 where tiny turbocharged engines like the Honda will get much better mileage but get used to the sound of a sewing machine.