Manual Trans vs Auto - Oil Consumption

[buster]

I believe I read in my old toyota manual that cars with manual transmissions can consume more oil than automatics. I don't remember what their reasoning was. Has anyone heard of this?

I don't down shift that much. I usually take it out of 3rd and put it into neutral when coming to a stop and use the brakes. I know some people drive differently.

 

[eljefino]

When my saturn burned oil (rings) I'd get a nice big gulp (blue smoke bomb) after descending a hill in gear. Lots of vacuum doing that.

I don't downshift, but I don't freewheel either. I get a fuel decelleration cutoff that saves gas compared to coasting.

 

[punisher]

Yup.

Some with manual transmissions use engine braking instead of their real brakes. The high engine vac pulls oil past rings and intake valve seals (not to mention punching the occasional rod out of the block).

Not an urban legend.

 

[JHZR2]

Even if you do not downshift, just letting off of the throttle likely creates more vacuum, simply because of the mechanical versus fluid coupling.

However my saab, for example, which is MT shows zero consumption over 10-14k.

 

[Bluestream]

Originally Posted By: buster
I believe I read in my old toyota manual that cars with manual transmissions can consume more oil than automatics. I don't remember what their reasoning was. Has anyone heard of this?

I don't down shift that much. I usually take it out of 3rd and put it into neutral when coming to a stop and use the brakes. I know some people drive differently.


Your method of driving a standard id correct. Some manuals do use more fuel due to the gear ratio. My 1978 Pontiac Trans AM with 4 speed man and WS6 Special edition package used more fuel than the same car with a 3 speed auto.

 

[440Magnum]

Originally Posted By: buster
I believe I read in my old toyota manual that cars with manual transmissions can consume more oil than automatics. I don't remember what their reasoning was. Has anyone heard of this?


High manifold vacuum when you lift the throttle during every shift.

Also more engine braking (high vacuum) than with automatics since the automatic's torque convertor slips quite a lot during deceleration.

But all that said, the difference really shouldn't be noticeable in a healthy engine.

 

[UncleS2]

Let's not forget those little Banzai Runs up near redline ever so often. After all, we *do* have to keep the soot blown out of it- right? Right!

 

[Rick in PA]

Originally Posted By: Stuart Hughes
Let's not forget those little Banzai Runs up near redline ever so often. After all, we *do* have to keep the soot blown out of it- right? Right!

Ah, the "Italian Tune-Up"! (think Ferrari, Lamborghini, etc.) I recently introduced a younger buddy at work to this expression. Sometimes on that last leg to work, if we happen to be running in at the same time, we'll tune our cars up. Conditions permitting, of course.

 

[rslifkin]

Stuart - You mean we're not supposed to do that with an auto?

 

[meep]

I have often wondered if engines in manuals have a harder life... every combustion strike is hard-connected to the driveline (I know, there are springs in the clutchplate) whereas in an auto, if you get on it, the TC unlocks and those "strikes" go into fluid. Wondered if pins, conrods and cranks had an easier life in an automatic.

OTOH, typical 4 banger manuals get shifted at ~3000 rpm, whereas an auto will try to shift sooner. Higher revs in exchange for less torque during cruise.

I'm rambling. will quit...

 

[KrisZ]

The engine doesn't care where and how it's connected. The only reason we have rubber motor mounts is for our comfort not engine comfort.
On another note, I think that because engines with manual transmission operate at higher RPM and experience more compression braking, they develop less carbon and probably are less likely to have stuck rings.

 

[440Magnum]

Originally Posted By: meep
I have often wondered if engines in manuals have a harder life... every combustion strike is hard-connected to the driveline (I know, there are springs in the clutchplate) whereas in an auto, if you get on it, the TC unlocks and those "strikes" go into fluid. Wondered if pins, conrods and cranks had an easier life in an automatic.



You are absolutely correct- automatics are generally easier on the entire driveline (think about this from the other end- rear end or transaxle gears like the fluid coupling too, and the fact that the torque doesn't reverse directions every shift, hammering any backlash in the gear train). But again, the actual real-world difference in most cars is TINY and shouldn't make any noticeable difference in the life of most engines.

And if you think engines are oblivious to what load they're driving, go talk to people who have tried to retrofit autmobile engines for aircraft use. The harmonics between the propeller, reduction gears, and power impulses from a piston engine are very complicated and can result in unexpected failures, and you quickly begin to understand why production aircraft have stuck to tried-and-true low-RPM direct-drive engines so long. And you appreciate how much R&D went into the really big airplane piston engines of the 40s and 50s with their complicated gearboxes and supercharger drives.

 

[Ray Garlington]

Originally Posted By: meep
... every combustion strike is hard-connected to the driveline ...


don't worry about that one. Typically, you are over 2500 rpm or ~42 revolutions per second. Since every cylinder fires once every 2 revolutions, you are talking about 84, 126 or 168 firings per second (for a 4, 6 or 8 cylinder car). That smooths things out pretty well, not to mention the heavy flywheel involved. There is no slippage at the clutch.

 

[cchase]

This is ridiculous to consider that the engine wears differently with an automatic vs manual transmission based on the viscous coupling in an auto transmission vs gears in a manual.

The engine does not know or care whether it is connected to gears or hydraulics in this respect. By the logic people are using to come to this incorrect conclusion, a manual transmission car will feel rougher going down the road, too, the engine will shake more, etc etc.

Not to mention there's a huge flywheel on cars that damps out any response like that if it did exist, which would probably imply the engine was rotating at something like 5 or 6 rpm... not 2000-3000 rpm.

 

[440Magnum]

Originally Posted By: cchase
This is ridiculous to consider that the engine wears differently with an automatic vs manual transmission based on the viscous coupling in an auto transmission vs gears in a manual.

The engine does not know or care whether it is connected to gears or hydraulics in this respect. By the logic people are using to come to this incorrect conclusion, a manual transmission car will feel rougher going down the road, too, the engine will shake more, etc etc.

Not to mention there's a huge flywheel on cars that damps out any response like that if it did exist, which would probably imply the engine was rotating at something like 5 or 6 rpm... not 2000-3000 rpm.


Sorry, but engineering says you're wrong in saying there's no difference to the mechanical parts. Its NOT an "assumption" on the part of those of us who are pointing out the phenomenon. You can't feel the impulses that are involved. On the other hand, the basic conclusion is right: at the low horsepower levels found in cars and the relatively high RPM involved, its just not going to matter in the life of 99.9% of the vehicles on the road.

But these things DO matter when you start talking about the kind of torque and horsepower levels and much lower RPM found in things like medium-speed diesel ship propulsion systems, stationary power, aircraft, and the like. Fluid couplings or diesel-electric coupling systems do make a significant difference in how things are designed, and in how they fail if the design doesn't account for those differences.

The issue is "down in the noise" for car engines, but it isn't like it doesn't exist at all.

 

[buster]

I've heard that engines with manuals last longer....go figure.

 

[meep]

Originally Posted By: Ray Garlington
Originally Posted By: meep
... every combustion strike is hard-connected to the driveline ...


don't worry about that one. Typically, you are over 2500 rpm or ~42 revolutions per second. Since every cylinder fires once every 2 revolutions, you are talking about 84, 126 or 168 firings per second (for a 4, 6 or 8 cylinder car). That smooths things out pretty well, not to mention the heavy flywheel involved. There is no slippage at the clutch.


No slippage, but the couple of times I got into clutches years ago (VW beetle, late 90's subaru) there were a series of coil springs arranged in a circle, axis inline with rotation, that were very stout. Maybe 6 of them. Seemed that their purpose was to provide partial isolation of rotational impulses.

Magnum brings up a great point. Anyone ever wonder why the true BMW gearheads never go the route of underdrive pulleys? Driveshaft fractures resulting from poor harmonics. They stick with oem.

KrisZ... didn't mention engine mounts anywhere...?

AFA rpm/frequency of impulse. Well, the faster it turns, the less vibration WE perceive, but the connected hardware still feels. 2 strikes per engine revolution in a 4-cyl. multiply that by the gear ratio and it goes down the line.

Must agree though, these factors are likely in the noise in real world. Driver habit probably a lot more of a factor-- manuals owned by enthusiasts might get run harder. Manuals suffer lugging by folks that shift too soon. Thrust bearing/plate wear causing driveshaft failure (does anyone recall those-- seems like the 4cyl s-10 suffered there?).

Mike

 

[meep]

oooo I got a good one. No load high-revs is harder on piston/pin assemblies than loaded high-rev. So, that 4th-to2nd heel-toe-shift that blips 5k on the tach as you approach the hairpin... wails on the OTHER side of the pin... and i'm not making this up. Many rev limiters kick in much lower in P/N than in D in an auto for this very reason.

An auto won't, in normal driving, ever expose an engine to this condition.

 

[cchase]

Originally Posted By: 440Magnum
Originally Posted By: cchase
This is ridiculous to consider that the engine wears differently with an automatic vs manual transmission based on the viscous coupling in an auto transmission vs gears in a manual.

The engine does not know or care whether it is connected to gears or hydraulics in this respect. By the logic people are using to come to this incorrect conclusion, a manual transmission car will feel rougher going down the road, too, the engine will shake more, etc etc.

Not to mention there's a huge flywheel on cars that damps out any response like that if it did exist, which would probably imply the engine was rotating at something like 5 or 6 rpm... not 2000-3000 rpm.


Sorry, but engineering says you're wrong in saying there's no difference to the mechanical parts. Its NOT an "assumption" on the part of those of us who are pointing out the phenomenon. You can't feel the impulses that are involved. On the other hand, the basic conclusion is right: at the low horsepower levels found in cars and the relatively high RPM involved, its just not going to matter in the life of 99.9% of the vehicles on the road.

But these things DO matter when you start talking about the kind of torque and horsepower levels and much lower RPM found in things like medium-speed diesel ship propulsion systems, stationary power, aircraft, and the like. Fluid couplings or diesel-electric coupling systems do make a significant difference in how things are designed, and in how they fail if the design doesn't account for those differences.

The issue is "down in the noise" for car engines, but it isn't like it doesn't exist at all.


440, I agree with what you said. However, I made specific note that I was speaking in relation to an automobile and NOT in lower RPM, higher load situations such as you mentioned. My conclusion is based around the conditions I listed.

 

[BeanCounter]

I see little consumption (using no makeup oil) in my truck with almost 190,000 miles, and I see no consumption on my turbocharged car (using no makeup oil). Both are manuals.
Seems like this is splitting hairs for the vast majority of folks, but interesting topic nonetheless.