Can low rpm damage the engine?
 

Hi all
Newbie here.
I've been trying out low rpm driving as I call it. shifting my manual at as low rpm as possible without the engine stalling. It's a gasoline 1,3 liter engine, Kia Rio 2004. On one 50 mile trip I got 55 mpg.

Now the question is if I'm damaging my engine/clutch by this? I generally shift up at 2500 rpm but when lowrpm'ing it I shift up at 2000 rpm.

Any comments?

greetings

i don't think it will damage your engine if you remain sensible, what you don't wat to do is go below idle speed, or if you feel the engine is really lugging.

i generally drive around in 5th even at speeds as low as 50km/h = 31 mph the engine is than just a hair above 1000rmp, if i have to accelerate to a higher speed i do tend to downsift one or two gears, so the engine at peak torqe wich is between 2000 and 3000 rmp and as soon as i'm at the desired speed i skip straigth to 5th, even when i'm in 2nd or 3d the rmp's will come down and the momentum of the car is usually enough to allow smooth transition.... while cruising along your car doesn't need all that power, especially at low speeds.

my car is a 1.6 however and my previous car was a 1.3 wich actually had more power, but needed to be revved to get that.

so if it feels that the engine can cope i think you should be fine.

lunarhighway speaks the truth: as long as you're not lugging the engine (causing it to shake, shudder or buck when under load at low RPM), you're fine.

Congrats on 55 mpg - that's impressive!

And welcome to the site.

thanks
 

Thanks for quick replies!
Don't be too impresed by the 55 mpg. It was attained during a roundtrip on mixed highways with a few stops! I'll post some more tankfuls of mileage later so you can get a real picture.
This is a fun sport. Cool and slow does it!
greetings

It's a totally different kind of high-performance driving. The one we're all used to, that requires lots of noise and fast reflexes, is an immediate sort of thing. That gives right-now feedback in the form of not flying off the road because you're keeping tight control of a car that's running at the outer edge of its performance envelope.

Hypermiling takes a different paradigm, high-performance in that you demand not more of the car, but of the fuel that goes into it. Any idiot can make more power: just add more fuel. Getting more distance out of the power you have, now that's a different question. It's more difficult to do in my opinion, and the feedback is periodic if you're driving a vehicle that doesn't have instant mileage readouts.

So long as you're not placing a large load on the engine at low RPM, you should be fine. At lower RPM, the oil will form a thinner film between parts, and will have less ability to protect your bearings at high load. For the same reason, don't let the RPM drop below your engine's natural idle speed or you may begin to suffer camshaft and rocker arm wear.

All IMO, of course!

I am envious that all of you european people have access to cars with very small displacement engines. Dodge neons here have 2.0 engines and I read that export neons have 1.8 engines.

I guess many of us obese americans need the extra torque of a big engine to transport our mass to McDonalds and WalMart.

maybe it's got something to do with the transmissions? it seems automatic transmissions are more popular in america than in europe... automatics tend to waste some energy anyway, have fewer ratios and you can't really think ahead. in a manual car with a modest engine you'll downshift maybe a couple of grears and than put your foot down, to get out of harms way, in an outomatic you just put your foot down and the engine will have to cope before the transmission downshifts... anyway i don't know much about automatics, but my drandfather has one and the engine sound seems to scream "upshift" all the time

Upshifting is almost instant in modern automatics... and Auto transmissions (properly built and tuned) can shift much faster than any human can shift a manual, both up and down. Automatics also tend to eliminate human error. Missed shifts and incorrect shifting procedure are taken out of the equation altogether.

Modern automatics also aren't as dramatic energy wasters as previous types. If a 15% drive-train loss is assumed for a manual, the resultant figure for a Auto might be something like 16-17%, rather than the traditional 20%.

For fixed ratio transmissions, a manually controlled auto would be ideal (you can change the gears yourself if you please, and it reacts only to redline and 0 load).

For CVT's, unless you have a few specific gear ranges in mind, like an extremely low CV gear set, then a mid-range for road driving, and a high-range for racing application (for a multi-purpose vehicle), it's going to be an automatic regardless... unless you want CVT with a direct transaxle-engine connection, and a clutch, which is available, but pointless. A multi-range CVT would be prohibitively large and complex, and who really tows, drives normally, and then races their car? Not many. The extra weight would prove a burden in every situation. The extra complexity would prove a larger paycheck for the dealer you have to have service your transmission/transaxle.

Do you have a source for this? Anytime the converter isn't locked up there are hydrodynamic losses.

This lists the automatic as %5 to %15 less efficient (not %1 to %2):
http://en.wikipedia.org/wiki/Manual_transmission#Benefits

Well I have no idea, but to be devil's advocate...if the manual causes 15% losses and the auto causes 17% losses, that is much more than "2% less efficient." The losses are in fact (.17/.15 - 1 = .13) 13% greater.

Some automatics do lock the converter in every gear now, some don't of course. Its hard to generalize these days about transmissions, so many variations now.

Back to the original question, it would be good to have an oil pressure gauge so you could see how oil pressure varies with rpm, or even using very light oil like 0W20. Since most cars don't have one I imagine most cars are pretty safe using 1/2 throttle or less at any rpm over idle speed.
Ian

Fair Enough KJSats :)

I did learn from this discussion that aside from bucking (I think we all agree that a bucking engine is bad), there is a minimum rpm for adequate bearing oil coverage.

I do not have specific values for specific vehicles, but this diagrams the general idea:


Oil analysis and lubrication learning cennter

"This condition is represented by the equation ZN/P, where Z = viscosity, N = speed (rpm) and P = load. "
http://www.machinerylubrication.com/...eeve_fig_4.gif

The numbers weren't accurate to begin with.. there is no fixed percentage of losses that can occur through a given type of drivetrain, so the numbers were placed there as holders to show the actual point - that automatic transmissions are no longer the power-defeating POS's they used to be.

I thought this would be evidenced by the use of words like "assumed" and "something like".

Sorry for not making that clear.

Well, folks go to great lengths for a %5-%15 improvement, so I'm not ready not rule out POS just yet ;)

Remember, that drivetrain loss is frictional/heat loss... it's not linear. It's an accepted average.

In fact, the losses multiply as speed increases, almost parallel to speed.

Anyway - the point was that automatics aren't as bad as they used to be... they're nearly as efficient as manuals are. Manuals still have vehicle control and longevity in their favor though.

KiaRio ,
Welcome from me as well.
Enjoy your stay.

Cheers , Pete.

Here's a nice demonstration of the Z*N/P concept.

(Starting around 5:00)
http://www.youtube.com/watch?v=SovjQKq7NQo

Very nice shots of internal parts in motion.

If that's the case, idling has to be murder! Especially on cold starts...

RH77

I've been told not to idle the engine for extended periods as the chronic low oil pressure/flow can cause damage and premature wear. I don't remember reading anything on it though, and I've never had a need to actually test it.

The main point -- not only is idling a potentially damaging proposition (especially extended idling during colder temperatures at startup), but is innately inefficient. 0 MPG.

Luckily, there is plenty of research by well-respected fuel economy experts, on the topic of idling. Even if it's -30F without an EBH, I start up, throw it in gear, wait for the fluid to kick the auto into gear, and slowly drive away (then pop it into 2nd to get the most out of the fast idle).

The previous paragraph contains an important EcoMod reference: the engine block heater. If I only had access to a 120VAC plug anywhere I park. 365/24/7 -- but on a timer. In the winter, maybe 3 hours -- summertime is about an hour.

Nevertheless, the added warmth allows a variety of efficient post-start benefits: including improved oil viscosity and flow. End of story.

Bear in mind that the grid is more efficient than your engine.

RH77

When I start the car, cold or not, I let the engine RPM stabilize before taking off... this usually takes 5-10 seconds after it starts. This is usually enough time to grab the seat belt, put it on, and put the car in gear.

Does loading the engine at low Rpms damage an engine?
 

Yes Especially with age. my first three cars suffered this fate before I learned.
Your piston rings need a oil film, low rpms limits lubrication, and increases soot and blowby, both of which will further lower your lubrication. esspically if your car has over 150,000 miles, your better off getting power in the normal operation rang. when i was 16, i needed to get all over the place with very little founds so I did this EVERY WHERE I WENT all three of my first cars died of bad pistons rings. I used to get 40+ MPG AS A DELIVERY DRIVER!!! fast my friends i was fast and i was about efficiency. like its been said high milage is a diffrent kind of extreme on engines. Just becuse your not, go fast doesnt mean your not asking alot of your engine!! one thing you can do to help is ENGINE BREAK this helps suck oild back onto the cylinder walls.

1978 Elcamino 5speed 350, 30 mpg 253 hp has a truck bed:thumbup:

Welcome to the forum, ElTruckCarMan !