Does shifting at low RPMs really hurt the engine?
 

Hi guys, i have an AT and my daily drive is PURE traffic. My "average speed" reading on the gauge is usually just around 20kph.

So i tried experimenting on different shift styles, shift points, sport mode D on off etc, and such and the most significantly economical fuel saving i get is driving this way -

(1) featherlight throttle - never past 1600 rpm (unless uphill i let it go 2000, you can feel it anyway when the car needs more)
(2) driven in M mode - I shift when the arrow comes up which i recorded to be at 13kph to 2nd, 27.5kph to 3rd, 38kph to 4th, and 52kph to 5th. (i never reach 6th because of traffic)

Result, I normally get 15L/100km instead of the usual 18. So i get to travel about 260km before fuellin up rather than 215km.

Q.. i dont really "feel" the engine lugging, and if it DOES lug, like when going uphill, i give it more gas and let it hit 2k rpm. Point is i just accelerate really slow since its traffic anyway.

Is this in anyway "bad" for the engine or transmission long-term? Because i noticed my manual shift points are even earlier than D with sport mode off and an eased throttle.

Why is your fuel consumption so high? My BRZ is manual, but my Forester is auto and I usually get 11-11.5L/100km in PURE traffic.

About shifting points, I would just leave it in the D mode.

Shifting at low RPM in and of itself isn't bad for anything. The only thing bad in what you describe would be if you are lugging the engine at low RPM (basically below 2k). However, if you're very gentle on the throttle at those low RPMs, then that isn't an issue either. In heavy traffic, I often keep the car in 2nd, which has the engine well below 2k RPM, but it is either just idling along, or I'm using light throttle, so it doesn't matter.

Low RPMs aren't bad for anything. Lugging the engine at low RPMs is.

Also does 15L/100km really translate to 15 MPG (US)? If so, something is horribly wrong with your car. I can't even get that low mileage in a day of autocrossing and towing a tire trailer. You should be getting closer to 25 MPG (10L/100km) in traffic, especially in how you're trying to drive efficiently.

How are you calculating that mileage? I can not imagine any possible way to get that bad even in traffic. Fuel would almost have to be pissing out.

I get 28.3mpg (according to the gauge) in stop and go. Takes 1 hour to go 22 miles to work and an hour to go 22 miles home. That translates to 8.311469 L/100KM.

Unless he is checking instant mileage consumption and not average ...

That is why I asked where he is calculating it. Wouldn't be the first to do that.

If you have an auto why are you trying to manual shift it. Just let the car do the work. Else buy a stick shift.

I had a Honda accord. Drove in traffic a lot and idled it a lot to charge phone or run heat/air con. Averaged 19-20 MPG in it. On highway trips though it will easily hit 35 mpg.

I wouldn't worry about shit MPG in poor driving conditions with a lot of idling...

Actually I just did a few trips in my BRZ and getting around 32 mpg doing 70-80 on the highway. But my "average" is 17mpg.

Hi guys, thanks for the input on as long as acceleration is gentle (not lugging) that definitely helped as thats what I do.


And to those who ask about mileage, the local version of our car comes in kph and L/100km in the indicator (not mpg). translated to KM/Liter, I get about 5.6-6.2.
Similar to our yaris and even our 1998 land cruiser lol!

I dont think you guys have the same understanding of traffic as we do in the Philippines. Check out "Philippine traffic" on youtube. We dont stop and go. We just pretty much STOP 90% of the time and crawl to a go. There is no GO. theres just stop and crawl.

The literal crawl and go traffic in my country (philippines) begged for an auto.. :) I never hit the highway too

yeah i am super gentle with the accelerator and would also do the same 2nd gear you do :) thank you for the answer! yes 15l/100km translates to 15.6 mpg :)

couldnt the type of gas being used cause the more frequent fill ups and bad mileage? but that being said i have an AT as well and just leave it in AT when driving, i dont find the need to be in its "manual" mode and especially in the city where its stop and going but thats just me. i also average 600km a tank

exactly tcoat! take a look at philippine traffic on youtube. thats literally 99% of the road i commute in everyday. no freeways/highways too. :)

Don't lug the engine.

https://www.youtube.com/watch?v=soJe...ature=youtu.be

Basically, you have a slow moving piston but a fast and power explosion. That force of combustion has to go somewhere. You want it going to the wheels, but lugging results in combustion that can't effectively push down the piston and you just waste fuel and wear the engine.

Besides, the optimal operating range for our engine is somewhere in the 2,500~3,000 range, right? It sure seems that ways to me. If you're doing anything other than coasting on flat ground, I'd downshift and keep it over 2,000 until you want to coast again, then go to the highest gear.

Thanks Mazeroni! however, if i dont floor it, and go really gentle on the throttle, i dont feel the ''lug" at all, in fact its still quite smooth. Will that count as safe?

That's safe. You aren't automatically lugging the engine just because you're at a low RPM. What I said earlier is still true. Very light throttle application without bogging the engine is fine. Also keep in mind that modern engines are less prone to lugging as much as older engines. The wonders of Variable Valve Timing, etc...

This car makes a very unique (read: terrible) tractor noise below 2,000 RPM when you're lugging it. That's a good audible way to tell that you're being too aggressive with the throttle at low RPMs.

I wish I knew more on the subject. I don't think anyone can tell you for sure. If you aren't feeling it, I'd guess it's not terrible. The engine is strong and can take a lot of abuse. Also the engine mounts are going to absorb some of the vibrations from the engine, and the firewall and other insulation could be dulling any sounds of "strain."

You say that manually controlling shifts gives you better fuel economy. :iono:

It could be that the ECU wants to keep you in lower gears for the sake of the engine, and thus you are seeing worse fuel economy. Or it could be it wants the car to feel sporty. But a lot of this is subjective. I don't really know what "gentle" throttle means and am not entirely familiar with you commute....

When crawling in traffic, I'm typically above 2,000 and use engine braking to slow to a near stop. I don't like the engine being under 2K because to my ears it sounds unpleasant.

I don't even let my car idle because I'm so afraid of it dropping below 3000rpm.....


leevanf, you are fine, keep doing what you are doing. If it doesn't sound like a tractor you are fine. I leave mine in second sometimes and just start in 2nd because I get sick of the 1-2-1-2-1-2 crap. Just be gentle. There is no mistaking the sound it makes when it's actually lugging. Don't ignore it if it is though because it really is hard on the engine.

How is that engine rebuild going anyway?

yea I'm not sure why OP needs to go into manual mode during stop & go traffic especially considering how delayed & sluggish gear changes are at low RPMs, not sure what the point is with that. I would just keep it in D with Sport mode turned off so that it upshifts whenever possible if fuel consumption is really a concern and lugging the engine should never be an issue in auto mode, it'll downshift into 1st if it feels like it is required..

Lugging the engine can cause timing chain failure, and our boxer motors fire both cylinders on one bank before the other bank has a chance to fire. Great balance at high rpm, miserable balance at low rpm.

Is this the same effect on an inline 4?

Depends if the engine has a timing chain or timing cover.

An inline 4 will be more balanced at lower rpm but the consequence is an engine that is much bigger in length and typically much taller.

But I’m not sure why Subaru chose a boxer design over what porsche did with the flat(?) crankshaft.

Either way never lug your engines and they will never lug you.

Does shifting at low RPMs really hurt the engine?
 

Flat, boxer opposing, all the same thing. Not really sure what you are referring to with regards to the crank being flat. The Porsche’s are laid out the same as ours. Both engines will have half the cylinders at TDC at the same time. Our firing order is 1324 just like the 718.

maybe hes talking about the crank plane?

Does shifting at low RPMs really hurt the engine?
 

I’ve got more time cleaning all the FIPG than pulling and disassembling. I got both pans cleaned, the timing cover cleaned and one head cleaned. Just need to clean the other head and then make a parts list and place an order. Toyota South East’s warehouse is right here in my home town so I should be able to get parts fast. I’ve got a hookup on pricing and the short block should cost me 1840. The problem is work has been nuts so I haven’t had the motivation to work on it on week nights so it’s been a slow project. I suspect I will have it back on the road this weekend or next.

I want to replace my DI seals but need that tool that is made out of pure gold. My seals actually don’t look bad but as cheap as they are I figure I may as well do them.

do the ATs really not force a downshift if you are lugging? Only time ive ever lugged an AT car is when i accidentally put it in 2nd instead of "D" (not all AT cars will even let you do that anyway)

never driven an AT twin though.

it will but the OP goes into M (manual mode) instead of letting D do its thing to manage the proper gear...in that mode it will only automatically downshift when revs are very, very low, below 1k rpms..

I'd suggest trying driving at a higher RPM to see if things improve for you.

I also have an auto and drive just about exclusively in manual mode. Even when accelerating gently, I am always at least 2000RPM before I will upshift. Once I'm at the speed I want and on a flat road, I can typically then shift up to the highest available gear. Even if the incline is very slight, I need to be a gear lower (IE, 4th gear at 55km/h).

For example, accelerating up to 50-60km/h I would accelerate through 1st, 2nd, 3rd (by 3rd gear I'm at the speed I want). Depending on the road incline, I would then cruise in 4th or 5th.

How far are you driving? Does your engine get up to temperature? I find this engine/transmission very inefficient at low temperatures (especially if it is below freezing outsite).

I get 15.6mpg in my Chevy Suburban which I am actually really impressed with. The Suburban is driven by my wife who is a stay at home mom so it doesn't do the daily stop and go crap.