Modern Automatics, Low RPM, and Engine Longevity

[carviewsonic]

During my career I was assigned a new work truck (Ford, GM, Ram) every 4 -5 years. The last three trucks I drove had 6 or 8 speed transmissions which would keep the revs low under most conditions. I would put 200,000 kms on them before they were passed on to be used as crew trucks. They would be auctioned off at around 400,000 kms.
These trucks spent most of their running hours at low rpm or even idling, because they were used off road on construction sites and driven in rural areas with gravel roads, so low speeds compared to highway driving.
The engines almost never had issues, running well at auction time while the rest of truck was worn out.

 

[Delta1]

I got a ride in an Uber ride in a newer Honda Civic automatic and I could not believe the low rpms.... the tach never went over 2000, even under moderate acceleration. Cruising at 40-50 kph was usually achieved at about 1100 rpm! Being an old school car guy I was shocked, and can't imagine all the wizardry that has to go into making that possible.

In my manual 2006 Saturn Ion, my lowest cruising rpm is 1500 in 3rd which nets me 40 kph. Any slower than that and I'll shift into 2nd and cruise at 2500 where the motor seems very happy. With the s/c the motor is extremely flexible, but even then I will never push it below 3000. I usually shift at 3500-4000 which for me strikes the balance between performance and economy.

 

[iCurious]

The purpose of add more speeds to reduce RPMs is due to mostly fuel economy..

The Engineers objective is to push higher horsepower engine using low tension rings, lower viscosity oils, increase gears in AT - all to just score on the MPG. I don't think they are striving for longevity.

 

[dfarr67]

2019 chev k1500, afm and all- engine ran fine, the 6L80 transmission was a disappointment from the get go and died at 220k kms.

 

[Patman]

I got a ride in an Uber ride in a newer Honda Civic automatic and I could not believe the low rpms.... the tach never went over 2000, even under moderate acceleration. Cruising at 40-50 kph was usually achieved at about 1100 rpm! Being an old school car guy I was shocked, and can't imagine all the wizardry that has to go into making that possible.

In my manual 2006 Saturn Ion, my lowest cruising rpm is 1500 in 3rd which nets me 40 kph. Any slower than that and I'll shift into 2nd and cruise at 2500 where the motor seems very happy. With the s/c the motor is extremely flexible, but even then I will never push it below 3000. I usually shift at 3500-4000 which for me strikes the balance between performance and economy.

That’s one of the reasons why I’m able to average 4.7L per 100km in my Civic in the warmer weather (and around 5.3 in the colder weather) If I’m not on the highway doing 100 kmh, I’m on roads where I can do a steady 60-80 kmh for long distances and at those lower speeds it gets under 4.0L per 100km because the engine is under 1500 rpm the entire time. I was never able to get this kind of fuel economy when I had my 06 Civic with the 5 speed automatic, it was always putting the engine at a higher rpm. The CVT in the Civic is the best thing for maximum fuel economy.

 

[SwampSurvivor]

Also consider that 3-4k rpms is not that high, even sustained. Engines are durability tested under much more stressful conditions.

Lugging, low rpm type driving is worse on the drivetrain than sustained 3-4k rpms IMO.

There's not a gas engine made in the last 40 years that can't run 3500 all day.

 

[tcp71]

I got a ride in an Uber ride in a newer Honda Civic automatic and I could not believe the low rpms.... the tach never went over 2000, even under moderate acceleration. Cruising at 40-50 kph was usually achieved at about 1100 rpm! Being an old school car guy I was shocked, and can't imagine all the wizardry that has to go into making that possible.

In my manual 2006 Saturn Ion, my lowest cruising rpm is 1500 in 3rd which nets me 40 kph. Any slower than that and I'll shift into 2nd and cruise at 2500 where the motor seems very happy. With the s/c the motor is extremely flexible, but even then I will never push it below 3000. I usually shift at 3500-4000 which for me strikes the balance between performance and economy.

a turbo 1.5 would keep the rpm down in that range. Let the scroll do the work. A lot of small turbo engines achieve 80-90% of max torque in the 1500-2000rpm range.

 

[PontiacHO]

Honestly, this is my first time hearing about the timing chain being an issue on the 2.7eb! I do know the earlier, first gen 3.5 had issues with timing chain stretch. And obviously the cam phasers on the second gen 3.5eb and the 5.4 triton. Although these were more so due to design defects more than anything.

Interesting to hear that your Tacoma revs lower. Is it a 4.0 V6? In my experience with driving a 19 4runner with that same engine, it tends to rev higher under load but it keeps the torque converter unlocked until later, meaning lower revs when cruising around town. It's a very comfortable shifting experience in my opinion, but some people dislike it.

Me too. The 2.7 has been the forgotten workhorse engine that gets overlooked by the 3.5 and 5.0 engines.

 

[Bonz]

Back in the mid'80s, I had a 1983 Ford Thunderbird Turbo Coupe, 5-speed. Spent summer job money one year during college on an intercooler and manual wastegate boost control. That car would absolutely rip with premium gas and having adjusted the initial timing to an additional 10° of advance. Brought my first kid home from the hospital when he was born well over a decade and 230,000 miles later. Specific output was much higher, however RPM was still limited by the factory red line as I did nothing to the valve train. I suspect vehicles back then had more margin for performance improvements versus modern cars which are, in my opinion, engineered much closer to what they are capable of from the start.

 

[PandaBear]

Without test data it is probably all guessing. I think running at low rpm in an automatic is not really a problem because if it needs more torque that the RPM cannot handle it will upshift. Remember we only use about 30-40hp to cruise a Taurus on highway at 60mph, and it came with a 140hp engine back then or more likely 200+hp engine today in similar size. Back then we may need to run at 2000rpm, because engine weren't as efficient in lower rpm (without variable valve timing), and also not having that many gear ratios. You wasted fuel due to plumbing loss, and if you lower the rpm you can reduce that, or you have to run more EGR for the higher rpm to compensate and limit that waste, etc.

A lot has changed and I would not mind cruising at 1100-1500rpm all day if it came from the factory stock this way.

 

[Hohn]

Lower RPM is even more reason to favor thicker oil.
I’m thinking about HPL 15w40 PCMO…

 

[TwoC400s]

This is a great topic. One thing over here in Mercedes land that is a known quantity is the 7 and 9 speed transmissions have shift "adaptations."

If you were to drive my wife's car, (she drives exclusively in "Comfort" mode, I'm not sure she knows how to put it into the other modes ) it would mirror the behavior of the OP's transmission, shifting as early as possible and keeping you in the highest possible gear for as low a speed as it could manage (generally about 1000 rpm).

Now if you were to get in MY car, where I often drive in Sport+ or in full manual select mode, you would immediately notice that (even in comfort mode) it holds shifts longer and keeps the car much closer to 2000 rpm before a shift.

 

[MCompact]

My Club Sport has a close ratio transmission to keep the M42 motor within its power band. 5th gear is 1:1 so the motor is spinning at 4000 rpm at 80. In contrast, the 9 speed automatic in the C43 keeps rpm below 2000 at the same speed.