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How bad is idling engine after draining transmission fluid.

509 Views 5 Replies 5 Participants Last post by  Danrudmin
I recently did a radiator replacement and since I was disconnecting transmission hoses decided to do a drain and fill at the same time.

Well long story short, I drained the transmission, installed the new rad, filled the coolant, and then revved the engine for about 10 min in park to get up to temperature and open the thermostat. But I did that before adding any ATF. Car seems to run fine for now. Did I damage the transmission?
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When you drain the transmission from the plug, you aren't getting the entire contents out of the transmission, there will be some fluid still in the torque converter and other internal parts. Don't get me wrong though, you're not supposed to run these when they are low. When the engine runs, it drives the transmission fluid pump as well no matter what gear you're in. What I would do is fill the transmission (if you haven't done it already) then drain it again, this time catch the fluid and strain it through a coffee filter and look for any debris. When you start seeing grits and sparkly bits, there is a problem. If there is little to none then I wouldn't worry too much, at that point refill it to the specified level and drive as normal.
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I drained the transmission, installed the new rad, filled the coolant, and then revved the engine for about 10 min in park
Dan! Oh, man.

Now, I've done things like this ... just not with an automotive transmission or engine.

Have you done damage? Probably, but no idea how much. It could be minuscule, on up. Fortunately, it wasn't in a driven gear.

100% agree with @HondaGoBrrr for subsequent actions. After you do what he said, just refill and drive it. Your van could possibly outlive my 2002 EX!

To give you a little peace of mind, my daughter was in an accident that tore up the ATF heat exchanger in her 2013 Corolla LE. Car was disabled, off into the grass by the side of the interstate, and she left it running while I drove to the wreck site, which took about 45 minutes. It already had pumped out all of the ATF that it could have, into the grass. I was amazed not to hear any metal-on-metal noise, nothing. Just the engine purring at idle. I've always been curious ... had I taken possession of the vehicle (it was totaled by insurance), I'm pretty sure that Corolla's A/T would have run again. It was making zero noise from being run at idle for so long without ATF.

The key for your and her situations, no load.

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I’ve done worse and didn’t cause damage. I started my Mazda accidently when laying on the remote start key fob while under the car with the trans pan was off. It was on for only a minute maybe but the remaining transmission oil came spilling out all over me and the driveway. Possibly dried up the pump but only for a few seconds. Gave me a heart attack at the time but one year later the car drives fine. At least you kept the hoses connected and didn’t put it in drive. If anything got damaged it would be the trans pump and you would start hearing a whirring noise if that happened. You can read all kinds of horror stories on the internet but not sure how many of them are true or just some good story telling.
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many moving parts inside the AT unit that need lubrication, even at idle in park.

Like mentioned above, there was still "some" oil in there, maybe not enough to do a full re-circulation cycle but it wasn't bone dry.

if the van drives and shifts fine with no noises, apologize to the van and go buy a lotto ticket.
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Thanks for all the kind words everyone. Crossing my fingers.
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