Turning off your car at 55 mph


ok4450, Your 2 cars must die when turned off or at least very soon. My old van will keep turning up to 24 seconds, I don’t know how much longer. One of these days I will find a looong hill and try it.


You’re right, as I wrote, this is an old prank. It probably worked only with engines with carbs instead of fuel injectors, but it DID work if you shut the engine off at highways speeds in drive. I’m not trying to solve any puzzles, just offer anecdotal information in response to the question.


I’d like to hear the minute details behind how you are performing this test, including any actions by you about the ignition switch during this coasting spell and what you’re doing with it at the bottom.


It’s very simple, I turn the ignition off and when I get near the bottom of the hill, I turn it on and the engine fires right up! One thing I haven’t mentioned is the van is a 1996 Dodge 2500, 5.2 V8, with automatic transmission. I have had it since '96 with very little upkeep, like it very much, and plan to keep it for a while longer. It has 138K miles.


That still does not clarify if for me. You state you turn it back on. Does this mean you turn the key to the RUN position only or are you turning it to the START position first?

Try this. While coasting downhill turn the key off and then back on very quicky. If you see the tachometer bobbling a bit for a few seconds and it settles on 0 then the engine is not being rotated.


Since I had essentially the same results as EllyEllis, I’ll add:

  1. car in “D” (or “2,” as appropriate for speed).
  2. Turn key from “IGN” to “ACC ON”
  3. Wait (up to 20-Mississippi) and observe PS,PB function
  4. Turn key back to “IGN” (no starter engage)
  5. Drive away.


meanjoe, you are correct. At the top of a hill, I turn the ignition one notch back to “OFF”. Not “ACC ON”. When I got to the bottom of the hill, 24 seconds later, I turned the ignition one notch to the right to “ON” and it fires up and I go on. ok4450. I see no point of turning the ign on after a second or two, I can tell it is holding the car back, and the brakes and power steering both are working. I have now tried this 4 times and never had to use the starter. Bear in mind my van is a '96.


Are we clear now? Some automatics will push the engine for at least 24 seconds? I think it will push (keep the engine turning) at least until the speed gets very low. I will try this when I find a long enough hill. It takes a long hill because the engine holds the car back


No idea on your vehicle and by this logic this means that your car can easily be bump started or pulled with a rope to start it in the event of a run down battery.

This also means that coasting in DRIVE with the key in the run position means the tachometer is also showing an RPM reading although it may be low or jumpy. Does it?

What I flat do not understand is how pressure is being maintained in the transmission hydraulic system after more than a few seconds. If there’s a technical explanation for that I’d like to hear it.


I coast in drive with the ign OFF, not RUN. Doesn’t everybody coast downhill with the Ign in RUN position? I doubt if it could be bump started but haven’t tried it. I might some day.
As to your 3rd comment, I don’t either.


No idea on your vehicle and by this logic this means that your car can easily be bump started or pulled with a rope to start it in the event of a run down battery.

No, I’m not saying that at all.

I’m saying that, once the vehicle is in torque converter lockup, it won’t spontaneously unlock when power to the engine is lost. That’s a different matter than bump-starting.

A good comparison is a vehicle (like a moped) with a centrifugal clutch. There will be no connection to the wheels until engine RPM is high enough to overcome the springs in the clutch. Once the clutch engages, however, the engine and drivetrain would be linked, and killing the engine would not separate that linkage.


This is not a moped. Converter clutches require hydraulic pressure (Lots of hydraulic pressure) AND electronics to achieve lockup. Once engine power is lost the vehicle slows the transmission can no longer supply enough hydraulic pressure to keep the clutches applied. The vehicle will then coast as if it was in neutral.



The centrifugal clutch is a different ballgame though. Couple of weights in a shell with a purely mechanical function that requires elevated RPMs to even operate at all.

I’ll have to remain dubious until it’s explained to me where the high fluid pressure that is required to squash the clutch plates together comes from along with clarification about low speed converter lockup, which normally occurs around 45 MPH or so as far as I know.


Regardless of anyone’s comments that “this shouldn’t happen!”, it plainly does. Enough people (including myself) have verified that their engines keep turning for some time when trying this. Based on comments, it appears that Ford vehicles ‘decouple’ fairly quickly, while Mopars tend to stay engaged for longer. Different transmission design?


oblivion, you are correct. Someone here keeps talking about thhe torque converter lockup. I am pretty sure that when I turn off the ignition that the converter unlocks.


The two examples I posted involve a Chevy also.

This brings up my question about the tachometer. While coasting in gear with the key in the RUN position does the tach needle sit on zero or does it show a low or jumpy RPM number?

If the tach is on zero then the engine is not rotating. If the needle is bouncing around or showing a low RPM reading then it is rotating.


ok4450, While coasting in gear with the key in the RUN position the engine would be running on it’s own power. Everybody does this every time they let up on the gas. I have been talking about going downhill with the ignition OFF. I doubt if the tach shows anything with the ignition off. I do not have a tach so I don’t know.
But “read my lips” while going downhill with the ign OFF, I have gone 24 seconds and the engine was still turning. When I turned the ign ON the engine fired up and I went on my merry way. There was no thump, no backfire, no sound or feelinng of any kind. Are there any questions still?


You ask about coasting in Drive with the ignition in the RUN position. Doesn’t EVERTBODY? I don’t know anyone who turns the ignition to OFF every time they slow down.


Oblivion, your statement above backs up what I have said several times on here. I haven’t seen where transman has conceded yet tho.

.b (1) : to acknowledge grudgingly or hesitantly <conceded that it might be so. (2) : to relinquish grudgingly or hesitantly


tardis, I believe you are correct. Speed, not time is the factor.