Weird RPMs... Happening to you?

[indus49]

I take the highway for part of my commute, and noticed something strange. I leave my house, and within a couple of minutes I'm on the highway, going about 70. My RPMs at this point are about 3,000, maybe a little over.

In another 3-4 minutes, my car decides to calm down, and now it only takes 2700 RPMs to keep my car going the same way...

Could this signal an (impending) problem with my transmission? Or is this just the engine/transmission finally warming up? Has anyone noticed this type of behavior? I have the 4 AT.

[Ever Victorious]

The torque converter on my old Kia would do that... it would take a while for the transmission to finally realize I wasn't accelerating anymore and engage the gears as opposed to... well, whatever the hell an automatic does.

(Any wonder why I picked the 6-speed?)

[proxim2020]

When I was younger, my mom had a Hyundai that would do that. The little car would roar down the highway for about 5 minutes and then quiet down. The transmission wasn't realizing that the user wasn't accelerating anymore and would stay in it's current gear. Even if you took your foot off the pedal completely. She didn't bother with getting it fixed because she didn't want to pay $500 in diagnostic charges.

[skoobahead]

Strange...Sounds like an electronic transmission issue.My CVT is turning at 2400 RPM at 70 mph. RPM's steady as a rock.

[Jrscherer]

I've had the same thing, it's either that it doesn't get that it isn't accelerating, or it's the fact that it's finally up to true running temperature which is one thing I kinda with the Versa had, a normal temp gauge. Oh well, guess I'll just need to get used to it.

[BenDupre]

It's not the transmission, it's the torque converter. It's taking a while to "stall". My Sable did this also.

A torque converter allows the flywheel and transmission to spin at different speeds, the way a clutch does, but using hydraulic fluid and a turbine instead of a disc and pressure plate. It's designed to "stall" once the car gets up to speed. When you see the engine turning 3k RPMs, the torqueconverter is still slipping. When you see it drop down to 2700, it has "stalled" meaning the flywheel and transmission input are turning at the same speed.

I'm not 100% sure whether it's a problem or not. Ideally, the converter will stall quickly when you reach speed, or even before. It should slip only when the engine doesn't have enough torque to turn the transmission. When it's not stalled, it's wasting energy. Which is the main reason why manual transmissions are more efficient than automatics.

Ask your dealer about it. But be prepared to get the line that "that's normal". I really don't know how you will get an honest answer, mechanics are almost as honest as salesmen.

Any mechanics out there who aren't insulted by my comments want to give an opinion?

Ben

[SVersaS]

i have a 4AT also and i havent noticed anything like that. whenever i reach 70, im steady at 2900 RPMs always.

[skoobahead]

The" lock up" function of the torque converter is controlled electronically is it not?

[LA02MAX]

Yeah that's pretty much normal for all of the new cars with conventional autos. It's a feature that supposedly allows everything to get to operating temperatures quicker...My mom's '00 maxima 4AT does that when you first get up to speed and usually about 5 minutes after it seems to settle down. It's almost like it disengages O/D for the first 5 minutes....

[BenDupre]

Skoob,

It's not electronic. It's fluid dynamics, plain and simple. The technology has been 'round since the 1950s.

Ben

[skoobahead]

Hmmm...I guess things have changed since the 50's

"Carmakers took the torque converter one step further by adding a lock-up function beginning around 1980. Lock-up converters also contain a friction clutch that locks the converter impeller to the turbine, usually in higher gears. A solenoid-controlled oil passage, commanded by the cars powertain control module (PCM), locks and unlocks the converter based on driving conditions."


Modified by skoobahead at 7:15 AM 10/12/2006

[indus49]

Great... well as long as this is normal, I can deal with 5 minutes of inefficiency I suppose... This is my first AT, I used to drive a stick... Did I make the right choice?

[Ever Victorious]

Great... well as long as this is normal, I can deal with 5 minutes of inefficiency I suppose... This is my first AT, I used to drive a stick... Did I make the right choice?

No

But that's just me.

[BenDupre]

I agree with EV. IMO small engines don't have enough power to waste. Manual is the way to go.

Of course, I have a CVT and I love it. I would have gone with the 6sp if it wasn't geared so short. I like cruising at 75 mph with the enging purring at 2500 rpm.

Skoobahead,

Not all torque converters have a lock-up clutch. I guess I don't know for sure whether this one does but I suspect not.

Ben

[skoobahead]

No way!

Unless your driving a performance car.... go with the auto. Rowing gears in the Chicagoland area wears you down quickly.In addition, CVT highway cruising at 75MPH with tach only turning at 2500rpm rocks

My .02

[proxim2020]

No way!

Unless your driving a performance car.... go with the auto. Rowing gears in the Chicagoland area wears you down quickly.In addition, CVT highway cruising at 75MPH with tach only turning at 2500rpm rocks

My .02

It's a matter of preference more than anything. Either you will enjoy shifting gears or you won't be a huge fan of it. Either you're going to enjoy not having to worry about gears while driving or be constantly upset because the car's picking the gears for you that you don't necessarily want to be in. The Versa isn't a performance vehicle, but it can be. You just have to throw $ at it. Buy what's right for you (auto or man).

[hoangmn]

When you start your car, wait for the blue thermo icon off before you start driving. That's when you car is at optimal temp to operate. The car is computer control so temperature and other conditions will be calculated to make the engine work best.The SL with CVT is even more sensitive to these conditions. You have to pay more attention or your transmission will break sooner.

[BenDupre]

The SL with CVT is even more sensitive to these conditions. You have to pay more attention or your transmission will break sooner.

[skoobahead]

The SL with CVT is even more sensitive to these conditions. You have to pay more attention or your transmission will break sooner.

Hmmmmm