Been watching DIY videos on ATF drain/fill on sealed transmission. When drain plug is removed on cold engine, a fair amount of fluid comes out, much more than would be captured in overflow tube. How can this be because level should be below overflow tube on a cold transmission? Curious that nobody mentions why this happens. Thanks.
Lexus Sealed Transmission
- Thread starter artbuc
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edyvw
$50 site donor 2025
I think, I think, it is bcs. drain plug is at the lowest place in the pan, and the overflow tube is not.
If this is not clear, give someone else to do a fluid change.
Good question. I don’t have the answer, but I want to clear up some confusion.
The drain plug, and overflow tube are in the same location. You must remove the drain plug to access the overflow tube. I couldn’t really find a picture to show this, but the video sort of does starting at 1:25
The fluid level should be below the tube when the engine/transmission are cold .. yet, more fluid than the tube holds, drains out when you remove the drain plug. How? Not sure. I just did a drain and fill on my ‘21 rav4, and experienced the same. For my rav, Toyotas adjustment range is 95f-113f, and I’m pretty sure my scan tool said the fluid was 77f when I started draining too (for the initial drain, not for adjustment. I started adjustment at 96f)
The drain plug, and overflow tube are in the same location. You must remove the drain plug to access the overflow tube. I couldn’t really find a picture to show this, but the video sort of does starting at 1:25
The fluid level should be below the tube when the engine/transmission are cold .. yet, more fluid than the tube holds, drains out when you remove the drain plug. How? Not sure. I just did a drain and fill on my ‘21 rav4, and experienced the same. For my rav, Toyotas adjustment range is 95f-113f, and I’m pretty sure my scan tool said the fluid was 77f when I started draining too (for the initial drain, not for adjustment. I started adjustment at 96f)
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IIRC, isn't the engine running during checking of fluid? If there is a loop in the radiator, it might be now full, as is the rest of the transmission. But when draining, it's not running, most of the fluid has drained to the pan. Much less to do with fluid expansion and everything to do with running/not running.
But it's been a while since I dealt with the sealed trans on my Tundra (my Corolla I just add what I took out and have not verified level, don't remember the procedure).
But it's been a while since I dealt with the sealed trans on my Tundra (my Corolla I just add what I took out and have not verified level, don't remember the procedure).
The passages or cooler or other places the fluid is pumped are draining down into the pan.
For example, when I drain and fill my 6R80, i pump fluid back until it comes out the fill hole, then start the engine and add another ~2 quarts of fluid. When it gets to temperature it sits right at the cold/hot full line on the tiny dipstick in the fill hole.
For example, when I drain and fill my 6R80, i pump fluid back until it comes out the fill hole, then start the engine and add another ~2 quarts of fluid. When it gets to temperature it sits right at the cold/hot full line on the tiny dipstick in the fill hole.
I think this is the answer. Car is not running when you drain old ATF so sump probably has extra volume drained from the system. This makes sense when you consider you must cycle through gears to “load” system before duetting final level.
Not sure I understand your question. "Captured in the overflow tube"? What does that mean? Fluid sits in the pan when cold and not circulating.
Follow trans service procedure and you will be fine. Generally about 2.5 to 3 quarts is replaced unless you do a cooler line service.
I will say it is a dumb process. Shouldn't be so involved and error prone.
After trans reaches normal operating temp, sump level is above top of overflow tube and overflow tube fills with ATF. When trans cools down, sump level drops below top of overflow tube (premise of my question) leaving a small volume of ATF captured. That is the volume I was talking about. But, as we now understand, sump level probably is always above top of overflow tube because ATF drains into sump when car is not running.
I understand procedure…was just curious about the issue extra volume which drains from overflow pipe.
I understand procedure…was just curious about the issue extra volume which drains from overflow pipe.
In many cases the converter isn't completely full when the vehicle is off.
In some rare cases like the Dodge 46RE you've gotta check in N because it doesn't fill the converter in P. Granted, those have a dipstick but the point is the state of the converter drastically affects fluid level in the pan.
In some rare cases like the Dodge 46RE you've gotta check in N because it doesn't fill the converter in P. Granted, those have a dipstick but the point is the state of the converter drastically affects fluid level in the pan.
dnewton3
Staff member
When the car is not running, the oil in the TC and other parts of the fluid circuit will partially drain back to the trans pan (low point). So the fluid level rises above the spill-tube.
This is why you start the car, shift into D and R a few times, then begin the (temp related) spill-tube procedure. You want to fill the circuits in the "as running" state to set the proper fluid level.
This is why you start the car, shift into D and R a few times, then begin the (temp related) spill-tube procedure. You want to fill the circuits in the "as running" state to set the proper fluid level.
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What's wrong with 'measuring' how much you took out and replace same amount with 'new' fluid ?
Keep the bottles of 'new' fluid next to vehicle (over night) so their the same temperature.
Keep the bottles of 'new' fluid next to vehicle (over night) so their the same temperature.
That would be too easy.
The reason not to do it this way is if there's a chance that the fluid level was not correct to begin with. Possibilities include prior servicing of the transmission or related components, leaks, fluid under-filled from the factory, etc.
dnewton3
Staff member
I generally agree.
I've done it both ways, and here's my reasoning ...
- When I got my used Lexus vehicles, I had no idea what service (if any) had been done to the trans. So I did a proper "temp verified" spill/fill for the first OCI of the trans. That way I was assured the level was correct.
- Once I was satisfied that I had got the proper level set, the next several OCIs (just a few days apart) were done by measuring the volume alone. I did this only after the vehicle had cooled overnight, and the replacement fluid was sitting in the garage next to the car, so that the temps would be the same and therefore the volumes would be the same.
- Then, after those several ATF short OCIs (to bring the fluid to a high concentration of new fluid), I again did a final "temp verified" spill/fill and sealed it up for the next 35k miles or so.
People will debate this till the end of time but FWIW I saw that The Car Care Nut in a recent video recommends only a single transmission pan drain and fill every 60k. No need to do multiple drain and fills.
People overthink this way too much. The procedure is not precise at all, but many obsess over it as if every drop counted.
It’s quite simple really, put in some extra ATF in there, get the vehicle level, bring it to the proper temp, remove the drain plug and let the excess drain until the flow is no longer laminar and starts dribbling. And there is no specific size to the dribble, or anything like that. Once it starts dribbling, it’s at the proper level.
Example of laminar flow.
Example of a dribble:
It’s quite simple really, put in some extra ATF in there, get the vehicle level, bring it to the proper temp, remove the drain plug and let the excess drain until the flow is no longer laminar and starts dribbling. And there is no specific size to the dribble, or anything like that. Once it starts dribbling, it’s at the proper level.
Example of laminar flow.
Example of a dribble:
