Having MPG issues, whats wrong?

What makes you say 1900 is the sweet spot?

 

And for those non-haters. Here's a side view pic to show off the tires. My daughter is in the pic for size reference and to keep her occupied (she said cheese, kinda).

 

From what I've read 1900 is the optimum rpm at highest gear before the engine peaks over and starts sacrificing energy to heat. Although each engine type is different it gives a good reference point (+ or - 10%).

 

Okay great. Good to know.

 

Hey, I'm really glad you eventually figured out the problem has to do with aero and force balance and not just kinetic energy. That was my original point, you through out an equation for kinetic energy which has little if anything to do with the problem of highway mileage. It is all about force balance, specifically aero drag and rolling resistance. The former becoming the dominant effect at higher speeds, the later at lower. Kinetic energy really only comes into play in acceleration and deceleration as one would consider in city mileage.

Take the time to think through problems before just throwing out an equation that seems to have the right relationship and you'll do fine as an engineer.

 

Simply put, if you want better mpg, go easy on the skinny pedal. Or as OZ said buy a Prius. I get 17-18 but I drive like a bitch. Engineers...

 

MPGs don't have be that bad. I have a mostly "stock" truck with a 6-speed manual, about 250 lbs of gear in the box and BFG KO2s at 45 psi and have managed up to 9.5 l/100 km, 25 mpg (US) highway. You need to drive carefully and try not to go too fast, drafting a semi doesn't hurt either. Driving aggressively can cut mileage by 50% easily. I use a scangauge with one display set to monitor average l/100 km and one set to instantaneous l/100 km.

Empirically, the best speeds for my truck seem to be in the range from 75 - 90 km/h, with speeds faster or slower being worse. Stop and go traffic is a killer.

 

She looks PISSED!

 

I realize the point you were trying to make but simple KE equations are used all the time to compare moving objects. IE: energy it takes to move from 0-40 mph vs 0-70 mph. That's the point I was making, just like comparing a handgun bullet to a rifle bullet, the handgun bullet has more mass but the rifle bullet has more velocity and thus more energy, thus takes more energy to get it moving that fast (hence larger casing with more powder).

 

Yeah, she gets that from her mother.

 

Absolutely agree. Just didn't see much relevance to the question of speed vs. fuel efficiency unless of course talking about stop and go traffic where it becomes really important. For highway it really is almost entirely about force balancing of drag and friction against the output of the engine and drive train.

Anywho, sorry to get off on the wrong foot about fundamentally rather pedantic things and dragging your thread off topic My fault for nit picking.

Oh - and as I mentioned earlier definitely verify the right tire pressure if you haven't already. The LT vs P load curves are very different resulting in roughly 45 psi on our trucks for most LT tire sizes and 30 psi for most of the stock P tires. Worth updating your door tag if you ever take your vehicle places for service or you may find someone "fixes" your pressure for you back down to 30 psi.

Cheers.

 

So... About those MPGs......

 

Although it seems you have improved your mpg via driving style, here are a few other ideas for potentially more improvement. I'm not sure how many miles you have, so some of these may not be as relevant to you as they were for me:

1. Use 91 octane fuel- From my experience and some others on here it will give you about 1 mpg boost (whether that is worth it or not at current fuel prices is up to you). But I have also noticed the truck just runs better on 91 vs lower octanes. Edit:DVexile also pointed out the ethanol content is what affects mpg between octanes, if your lower octanes do not have ethanol then 91 may not be helpful for mpg.
2. Clean your throttle body and MAF sensor - Super easy to do (remember to be careful with the MAF sensor).
3. Clean or change your air filter - pending how dirty it is this could potentially help mpg, but it is a good thing to do regardless. I think Toyota recommends changing it every 30k.

Here are a few things I did recently with my 60k (and 30k) maintenance, which I noticed a boost afterward. Obviously follow the maintenance schedule, but if you are due for 30k or 60k maintenance, these may help too.
1. Change spark plugs
2. Change differential fluids
3. Change motor oil (full syn) & filter (toyota oem) - every 5k

Hope some of these may help you too!

 

So the octane itself really doesn't improve mileage at all. BUT, in many places the 91 octane fuel has less ethanol in it than the 87. And it is that lower ethanol content that can improve the MPG. If, however, you live someplace where the ethanol content is the same for all octane ratings then running a higher octane won't actually help your MPG.

 

Congrats. That's not a simple thing to do.

 

Good point! I forgot to mention that the lower octane fuels where I live have 10% ethanol. So 91 gives me better mpg, but may not for you pending the fuel options where you live. Thanks DVexile for catching that.

 

Once you factor in the increased cost for premium you are probably losing money by running 91 vs what regular.

 

Thanks, that was a tough test (8 hours).

 

I would like to say Thank you. That is great website.
Does anybody know what is out our Truck Cd - Coefficient of drag?

My Golf had 0.29 I never found that for Tacoma. On the Wiki leaks they only have Toyota Truck at 0.44 and there is no way 2gen is that bad. Sequoia is 0.31. So our truck has to be similar to it.

 

Right you are. Hence my original statement "(whether that is worth it or not at current fuel prices is up to you)"
However, I don't personally run 91 for increased mpg. I use 91 because its the only fuel around here that doesn't have ethanol and for the noticeable improvement of how my truck runs on 91 vs the lower octane fuels in my area.