By on February 18, 2010

Monty writes:

I have a question regarding cold weather starting my 2001 GMC Sierra P/U. When the temperatures dip to -40 C (-40 F) wind chill is there an advantage to starting my truck and leaving the transmission in neutral (with the parking brake on)? It has 235,000 kms and is the S/L version (strippo) with the 4.3 V6 and 4 speed auto. The transmission is original and I had the fluid changed at 215,000 kms.  I bought it with 206 on the clock, not sure what was done before me, but I check the fluid regularly, and it has remained the same colour and viscosity as it was originally.

The problem is that when I start to drive after the vehicle has been warming up for 5 minutes, it takes another 10 more minutes or so for the transmission to shift up into 4th gear. This adversely affects my fuel economy, and I’m worried that long term this may not be good for the transmission. I haven’t noticed too much of a difference this week warming the truck in neutral, but it’s been so cold that I don’t know if it’s helping at all. My father, who is in his 80’s, always advised to warm the transmission in neutral in winter conditions, but I’m concerned that he may be using a trick from the 40’s or 50’s for manual transmissions, and it may not help with the automatic version. And yes, I use a block heater once the nighttime lows exceed -15C.

Sajeev answers:

So the concerns presented here are fuel efficiency and transmission durability. Luckily, nothing is wrong with the truck.  Perhaps you’d like to join me down in the balmy Gulf Coast?  Because the truck would be oh-so-much happier down here, and let me tell you why: vehicle computers prevent overdrive engagement until the transmission fluid (or engine coolant) reaches a certain temperature.  Or until a certain speed is crossed: my car shifts into OD at 55mph in near-freezing temperatures, even with no warm up time from my parking garage at work to the adjacent freeway taking me home.

As to idling in neutral versus park: there’s no benefit, if you let the truck warm up before you drive. The transmission doesn’t care either way, and neither should you.

Speaking of caring, let’s get back to why your truck wants to move down south: fuel economy.  As we all know, idling is a huge waste of fuel.  What’s less apparent is just how much fuel is dumped in a cold motor to keep the motor running properly.  Modern EFI systems completely ignore the O2 sensors until they reach a certain temperature, making an engine run like a richly tuned carburetor.  But this is a necessary evil, if you live in cold climates.

Obviously I’m kidding about moving due south.  We have a little problem with fuel economy with the A/C running at full tilt. So what’s the moral of the story?  Enjoy your truck, because it’s doing everything to keep you motoring safely for years to come.

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28 Comments on “Piston Slap: Frozen Solid, Yet Self Aware Edition...”

  • avatar
    Dan R

    I suspect driving it around when cold will waste less gas than letting it idle and get the transmission up to temp more quickly. Better for the motor too. Synthetic ATF may help the shifting.

    • 0 avatar

      Definitely (especially if you’re IN it). On ridiculously cold days (if the mazda hasn’t been in the garage), I’ll try to reprogram my head to NOT upshift so fast and get the motor heated up quicker.

      Good luck Monty — I DON’T miss living where it’s THAT cold . . .

  • avatar

    I think you might be right, Monty. Your pop was probably just saying “neutral” as in “not in gear”. Park vs neutral should make no difference.

    Two things:

    1. Your truck does not feel windchill. Machines do not get colder than ambient temperature, no matter how hard she blows. Sorry, that’s a nitpick of mine.

    2. If you idle your engine to warm the truck up, remember that your engine may be toasty, but your tranny is still frozen. Drive gently.

    • 0 avatar

      Not true: wind-chill is real, in a way. If machines didn’t feel it, your radiator wouldn’t work.

      What it will do to equipment is syphon off any heat above ambient that has accumulated.

    • 0 avatar


      Wind chill is real only in the same sense that perception is reality.

      Radiators work due to temperature differentials and a combination of radiative, conductive, and convective heat transfer.

      A “wind chill” is a made-up temperature based on human perception. It is the temperature which would make you feel equally cold without wind as the warmer actual temperature makes you feel when factoring in the wind. “Heat index” is the equal/opposite effect taking into consideration the relative humidity and its adverse impact on the evaporation of perspiration.

    • 0 avatar

      Wind chill will make a difference in that your vehicle will cool off more quickly – until it reaches ambient temperature.

      Once the vehicle is at ambient temperature wind chill will have no further effect. Except to reduce the effects of your block heater.

    • 0 avatar

      Yes there is a wind chill effect. But the number given by weather channel type, hardly relates to human beings, and even less so to things like cars.

      The faster the wind blows, the faster your car will cool down. But that number on TV you hear is bogus.

  • avatar

    I understand that auto manufacturers intentionally prevent automatics from shifting into upper gears for emissions purposes, since a cold engine and catalytic converter spews more than a hot one. More revs = faster to warm up.

    A block heater will help the car reach operating temperature faster, and if you plug it for only an hour before you go, the cost in electricity should be much less than the cost in gasoline to do the same thing.

    • 0 avatar

      Overdrive gears (which are sometimes band/strap activated) don’t like to operate at low RPMS in either cold or hot fluid temperature settings. It’s a stress/life expectancy thing.

      Course, I say this because of my experiences with Ford AOD transmissions and the aftermarket’s Kevlar OD bands. (Turns out the upgrade isn’t worth it.) Then again, OD transmissions have improved significantly since then, so who knows what cold weather and low RPMs means any more.

    • 0 avatar

      +1 on the block or engine oil heater. Will greatly speed up the warm-up. In northern Minnesota / North Dakota you automatically get one of these at 16 with your driver’s license. Especially if you don’t garage your car.

  • avatar

    Park and neutral are essentially the same condition in an automatic EXCEPT in park the output shaft is locked up to prevent the vehicle moving.
    Your transmission will warm up a lot faster when in gear. This is because the torque converter is “slipping” and thus generating heat. In neutral/park it is not slipping much because there is no load on its output. For safety though DO NOT put it in gear and leave it unattended; just drive it at moderate speeds.
    A manual transmission will warm up whenever the engine is running and the clutch is not pushed down. This is because the countershaft gears are always rotating and churning up the oil.
    So Dad’s advice is applicable for a manual but not for an automatic. Although most manuals are not a problem if a modern multigrade lube like 75W-90 is used.

    • 0 avatar

      Dad’s advice may have also been useful on some of the older transmissions where the front pump only was active in gear or neutral. This is no longer the case on modern transmissions to my knowledge.

  • avatar

    As everybody else has said, the car is fine, and there is no difference between park and neutral besides the parking pawl being applied in park to keep the wheels from turning.

  • avatar

    There *IS* a difference between park and neutral, in most makes of vehicle anyway.

    In Park, your ATF pump doesn’t turn. In Neutral, and in all gears, it does.

    Idling in neutral will circulate ATF through the trans and possibly the trans cooler. Unless you have an auxiliary trans cooler (usually included in factory tow packages) the trans cooler runs through the radiator which will warm the ATF in cold weather once the engine coolant warms up. Also, the pumping of the ATF should pre-lube the trans and will slightly warm the fluid via the pumping resistance at that temperature.

    • 0 avatar
      Eric Bryant

      In every transmission that I’m aware of, the main pump is driven from the outer shell of the torque converter – in other words, pretty much straight from the crankshaft. It matters not what gear the tranmission is in – the pump is turning if the engine is running.

      There are a handful of vehicles that also power a pump from the output shaft of the transmission such that the vehicle can still apply hydraulic pressure in the case that it is rolling but the engine is not running, but this is fairly uncommon.

  • avatar

    Have you considered adapting a block heater (you do have a block heater, right?) for your transmission?

    Anyone who lives anywhere that sees -40C regularly should really cough up the hundred bucks a block heater would cost, and might do well to consider a battery blanket as well. I’ve never heard of anyone using a tranny heater, but it might not be a bad idea.

  • avatar

    As someone who isn’t a numbers person, I’m amazed the Celsius and Fahrenheit scales match up at -40!

  • avatar

    OK ..Myself and my buddies have had lots of experience with that set up, a 4.3 and a 4 speed auto. 40 winters,driving in Ontario,tells me your truck is fine,just take it easy, until it warms up

    Monty, Automatics do weird things when their cold. Wind chill don’t mean squat. If your plugging in at -15, you don’t need more than a few minutes warm up, any more is a waste of gas.

  • avatar

    Thanks, Sajeev, and thanks to all for some good advice! However, I’m not taking this truck down south! And I wouldn’t go to Texas; it’s northern Arizona for me, where I could ride my bicycle all year long.

    Also, sorry everybody, but there seems to be some misconception about this sentence fragment:

    When the temperatures dip to -40 C (-40 F) wind chill

    It should have read like so:

    When the temperatures dip to -40 C (-40 F) plus the wind chill

    And I don’t care what anybody says about Wind Chill, because when the temperature dips below -40, and the prairie wind is whipping around at 30 to 50 mph, ITS EVEN FLIPPIN COLDER

    True story: My wife and I took one of our annual Christmas trips to the coast, some 25 years or so ago, to arrive in Regina Saskatchewan at noon in MINUS 46 degrees temps (and this was before windchill was a common phrase). When we left Winnipeg, at 4 am that morning, it was minus 42 locally; 2 hours later I pulled to the shoulder to relieve my bladder just outside of Brandon Manitoba, and the urine froze before it hit the ground. Seriously. I’m sure that the windchill that morning made the temperature equivalent to about minus 60. Trust me, if you haven’t been on the prairies for a winter cold warning, you don’t know what cold is.

    And the other point, which is that my Dad, who was a mechanic for several years, was actually referring to 50’s vintage automatics, which he says were static in Park, but once out of park would be spinning the converter and heating up. That’s what he says. Whether I trust his memory or competency at this point is another thing.

    Thanks to all; I will change the fluid in the tranny to the synthetic version, hopefully that may help. I do plug the blockheater in at night (it’s on a timer), and I usually only let the truck warm-up maximum of 5 minutes, usually less, and I drive it gently (which I do when it’s warm; actually I drive it gently all the time, having learned that lesson many years ago), and other than this one little problem, the tranny has been very good.

    • 0 avatar

      I pulled to the shoulder to relieve my bladder just outside of Brandon Manitoba, and the urine froze before it hit the ground

      If it was below -40C, you’re lucky that it was just your urine that froze. Last time I was in Winnipeg in the winter I feared my eyeballs freezing.

    • 0 avatar

      The prairies rock – seeing the northern lights, and pretty well every star, at 3am on a moonless night is just amazing… plus, Sask is great, if only because you can see Manitoba and Alberta at the same time….

      Anyway, as a truck driver, I can tell you even the Allison automatics refuse to shift into 6th until they’re warmed up properly. Of course, I don’t pay for the fuel,and given my job (garbage collection), what do I care about fuel economy – we’re lucky to get 2.5mpg on a good day.

      Lastly… Go Canada!!! May we kick the American’s butts!!

  • avatar

    Nice pic of the badge-engineered Chevy pickup!

    Although back then, I think that GMC did still have their own engines.

    Yes, keeping the transmission in gear will warm up the fluid faster as others have said. It will also warm up the engine quicker as it will put a slight load on it. An unloaded engine (esp. true for any modern diesel) has a hard time getting up to full operating temp, especially at those low temperatures when you are sucking every BTU of heat that you can out of the heater core.

  • avatar

    As was hinted at earlier, you should absolutely consider a heat pad applied to the transmission pan. That is standard equipment on vehicles that operate on the North Slope oil fields. I remember years ago the local Chevy dealer sold a fleet of trucks to somebody up there, but forgot to install the tranny heaters. The owners cried “Fowl” because none of their trucks would even move!

  • avatar

    -40 is cooler than we normally get also here in Sweden. But -20 to -30 celsius is kind of normal during the winter. I use a block heater (also in the summer to save gas, electricity is much cheaper than gas here) but as said before, the transmission is cold despite that. I drive everyday 5miles before the OD engage. But what can you do about that? You can debate the value of fully synthetic but it is indeed worth the price when it is really cold and I always use it in my car!

    HD Elecra Glide 1977
    HD TC88 rigid Swedish style 20″ over chopper
    Oldsmobile Alero V6 1999

  • avatar

    I’ve lived in the Black Hills of South Dakota my whole life. It gets incredibly cold here on a regular basis, and stays that way for nearly 9 months.

    Lots of people, especially those with remote start, will idle their car, but that’s mostly so it’s warm inside and it defrosts the windows. Until recently, I was not blessed with such technology, so I just started, let it run long enough to scrape the windows off and took off. Don’t rev the nuts off it when it’s cold, as the cold oil will offer you little protection. I kept it below 3000, your rev range will vary. Just did this until the heat gage got past the C level and then I drove normally (Which is to say, I drove as if I was being pursued by Satan and all the chariots of hades at all times)

    As far as the trans goes, it’s pretty much the same thing. Mine actually liked it better when it was cold. It had a bit of a hesitation and a clunk in the warm weather when shifting into drive, but when the fluid was nice and viscous in the cold weather, it worked a lot better.

  • avatar

    In my 94 Dodge pickup, the computer will not let it shift into overdrive til the trans temp reaches 60F and will not lock-up the torque converter til 70F, to prevent damage to the transmission. Your truck probably behaves the same and is operating properly.

    The Chrysler 727 automatic does not pump fluid in park but it does in neutral (the valvebody can be modified to change this behaviour). The trans in my truck is still based on 727 design, but I don’t know if it still behaves this way. Probably other automatics do or did act the same. That is probably where the advice to idle the vehicle in neutral when cold came from.

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