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KiaRio2004 06-10-2008 06:20 AM

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?


lunarhighway 06-10-2008 06:49 AM

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.

MetroMPG 06-10-2008 08:32 AM

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.

KiaRio2004 06-10-2008 09:15 AM

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!

elhigh 06-10-2008 09:33 AM


Originally Posted by KiaRio2004 (Post 33247)
This is a fun sport. Cool and slow does it!

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.

Geonerd 01-24-2009 02:30 PM

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!

amcpacer 01-26-2009 11:09 PM

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.

lunarhighway 01-27-2009 04:39 AM

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

Christ 01-27-2009 12:59 PM

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.

dcb 01-27-2009 01:34 PM


Originally Posted by Christ (Post 85332)
...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%...

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):

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