Tachometer and automatic transmission ??

As the proud owner of a new minivan (dull, I know) I realized that the “standard” tachometer that came with it is absolutely worthless for any purpose. I’ve driven the thing for at least 4 thousand miles and I’ve never even looked at the stupid thing. My question is: Is there a purpose (other than marketing) for having a tach in an automatic minivan ?? It’s not like a Tiptronic Porsche or anything, I could see having one there but I just don’t get it. Automotive appendix.
Am I missing something ?

Well, yeah, driving a minivan, I would say so.

To answer your question: Naw, it’s basically a carryover from the old days. The big cars my dad drove in the seventies were without a tach and it made the monster-sized speedo hard to read. The tach is there to fill in the space and look functional.

Sometimes it’s good to have a tach on an automatic-transmission car – especially if the engine is a bit underpowered. If you stomp on the gas pedal to pass somebody, and watch the tach needle jump quickly into the yellow, you know that you need to back off if the car doesn’t shift real soon.

It’s also useful in hilly areas, or when carrying heavy loads, or any time you’re putting a lot of strain on the engine and/or driving at speeds where you’re right on the edge between gears. The tachometer lets smart auto-tranny drivers save a little gas, wear and tear.

–Da Cap’n
“Playin’ solitaire 'til dawn
With a deck of fifty-one.”

      • Tachs on automatics are good for at least one thing - if you hit something that puts a hole in the transmission pan, you will see the engine speed slowly climb while the vehicle slowly decellerates, as the transmission fluid drains away. Then you know to pull over and stop and all you’ll need to replace is the transmission pan and fluid. Driving until the vehicle won’t move will do ugly things to the transmission bearings.
  • (All this is mainly a phenomenon with 4x4’s and/or teenage drivers) - MC

Some cars also have a button that you can press that will stop the transmission from shifting for as long as you hold it down. A tach might be useful there to let you know when you get to the redline.

The exact same topic was on Car Talk a few weeks ago - someone called to ask what purpose the tachometer on an automatic-shift Dodge Caravan served. Click and Clack said that tachometers do have an important function on luxury cars - it tells the driver that the engine is running. Chrysler, they said, has other ways of telling the driver the engine is running, so it’s just for show.

My '79 Volvo with automatic transmission also has a tachometer. I occasionally look at it and try to keep it under 2000 when accelerating - seems to improve fuel economy slightly, but it’s hard to say. I’d also think it’s a useful thing to keep an eye on when using the engine brake.

Yes, it’s basically a holdover from the days of manuals, but it can still be useful.
-Todays tiny engines usually have very narrow torque peaks. Driving at the rpm where the motor produces the maximum torque will save you a few pennies in gas.
-Keeping it under 4K rpm will substantially increase the life expectancy of the motor.
-Get used to the way the tach and speedo read relative to each other. Any variation from the norm may indicate a transmission problem.

  • erratic readings or a wildly jumping needle may indicate an ignition problem.
    -In limited traction situations (snow/ice) the tach will indicate an increase in engine speed (due to the slipping tires) more quickly than the speedo (if the speedo catches it at all).

OK, that last one is reaching, but it did save my butt last winter.

Happy motoring.

Or maybe they just want to make one instrument cluster for the entire line and save some money.

I think that it is there strictly for marketing purposes only. It seems to me that the space taken up by a big tach on the dash could be put to better use

“The philosophers have only interpreted the world in various ways; the point, however, is to change it.” (Karl Marx, 1845)

OK…good reasons to maybe glance at it now and then. And the slipping on ice idea isn’t a stretch at all but I usually use the speedo for that purpose.

As for “missing something” by driving a minivan, one of my other vehicles is a Harley, and that makes up for it nicely. It has a tach that’s actually useful.

      • This gets back to the bit about teenage drivers, but if you spin the engine too high usually the “brake” light goes on. - MC

The '66 Barracuda had a tach in the standard version and an intake-manifold vacuum gauge in the automatic version. That gauge was damn useful – I wish it were standard on all cars.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

Must qualify yourself. Depends on the vehicle. My car redlines at 6k. I don’t see a problem taking it up to 5k before shifting, if I’m driving aggressively. Some cars do redline at 5k and shouldn’t be above 4k. Then, we have Honda’s new S2000, which redlines at (I think) 9k and makes its power right at redline. Staying below 4k on that car would make you think you have a slow car.


We are the children of the Eighties. We are not the first “lost generation” nor today’s lost generation; in fact, we think we know just where we stand - or are discovering it as we speak.

Homer, I was referring to total engine lifetime (i.e. trying to wring 200k+ mi out of an engine), not catastrophic failure. This has absolutely nothing to do with a particular motor’s redline.

For a typical (~60 psi) oil pump bypass, 4k is about the point where engine friction loads start to overcome the oil film. Above this, cylinder wall, ring, and valvetrain wear increases exponentially. Now, if you’re sure that your engine is equipped w/ a high pressure pump (or the whole system has been designed or modified for high volume operation) then by all means tach it up.

And yes, by following this rule of thumb, you won’t be doing any “agressive driving” and your car will seem “slow”. So, if performance is more important than longevity (as it is to me), then disregard this ‘rule’ entirely. (Definitely a case of “do as I say, not…”)

My family has owned several cars in my lifetime, and I discovered a nearly-universal rule: automatic transmissions go with tachometers; manual transmissions go without. This is because of two reasons:

  1. Tachometers are a high-end item; automatic transmissions are a high-end item; it’s a match made in heaven.

  2. Folks who design cars are kind of dopey.

Okay, I’m sure my family’s car fleet is hardly representative, but it is still kind of weird. They included (over a period of roughly 25 years): a couple of manual-trans Volkswagen w/o tachometers, a couple of automatic Mercedes w/ tachometers, an automatic Volvo (don’t remember), two automatic Fords (one w/, one w/o). So I’m sure the narrow range of manufacturers contributes to the unrepresentativeness of my sample.

So basically, I’m just thanking y’all for covering this issue, since I’ve unconsciously been waiting for this thread ever since I figured out what a tachometer was in the first place.