How to Drain/Refill Automatic Transmission

One question I haven’t seen asked is why is the tranny fluid the only fluid on the whole truck that must be level checked at a specific temperature range?

Even if there was a dipstick, level check would require that temp range…right?

Obviously the dipstick would be nice if you’re concerned you have a leak and want to confirm or know how bad.

 

Because ATF expands when it's warm. That's why on vehicles with dipsticks there are typically a cool/cold mark and a hot mark.

As for being level? That's just to make sure that not too much or too little drains from the check drain......which sets up a little higher in the pan. In fact, some more recent FWD Toyotas actually have a "straw" that's threaded into the drain hole that must be removed after the check plug is. This straw sticks up into the pan an inch or so.

 

My understanding is that it expands/contracts significantly depending on temp and there isn't as much leeway re: being a little under or over filled as there might be with oil or blinker fluid.

Tranny dipsticks have cold and hot levels marked on them, so you can check at different temps...

 

The whole procedure seems daunting at first. But after you do it a couple it's not really the PITA that it seems to be. This thread is full of great information. But it's also got a lot of over analyzing and people trying to come up with alternate ways of doing things.

Follow the instructions and the guess work is eliminated and fancy tools and toys are not needed. And how often does one even perform this procedure? Not that often. So any inconvenience doesn't happen very often.

 

All the fluids in the truck expand when heated to some degree. Other fluids in the truck have hot/cold fill lines but think about it, those are not associated with specific temps (as far as I’m aware) and the tranny fluid is the only one that has a level check based on a *transient* temp on the way from cold to hot.

I guess the tranny fluid is the only one with particular properties that cause it to expand more than others in the truck, but I wonder why not set the level check procedure based on a normal operating temp once fully heated. Rather than the transient one. I’m sure there’s a scientific explanation but I’d be interested to hear it.

 

Given how the level is checked it's more likely to be done by a shop for most buyers, and trans fluid would take significantly more time to reach normal operating temps, if it ever does, would be my guess. So they picked a temp when they know the passages and tc would be consistently filled but wouldn't require an hour of shop time idling the vehicle. To be fair, last flush on my Chevy I had a hell of a time getting an accurate reading because of the dipstick dragging through puddles in the low-angle dipstick, so each method has its pros and cons.

 

If the procedure was envisioned being done only in a shop, would’ve made sense to pick a cold temp somewhere near room temp. It can still take a good amount of time to get up to the transient temp range on a normal day.

Anyway, enough about that, we can only speculate.

 

The factory manual for my 3gen states:

If the fluid temperature is below 45°C (113°F), proceed to the next step. (Recommended ATF temperature: 35°C(95°F) or less),
If the fluid temperature is 45°C (113°F) or more, turn the ignition switch off and wait until the fluid temperature drops below 45°C (113°F).

So, when read by techstream, the temp should be between 95F and 113F. Looks like you pretty much nailed it.

 

True, but the tighter your engineering tolerances, the less you can risk contamination. Gotta wonder how much moisture and other contaminates enter via the dipstick route.

 

This whole thread is dedicated to the 2nd gen.....Where does a 3rd gen procedure come into play here?

 

Actually la lot of people have tried that before. Issue is different folks have reported different temp ranges. The most accurate way is still to use the jumper. Unless you verify for your specific truck first, I suppose that would work too.

Not sure why, but ATF seems to expand / contract with temp more so than any other fluid. Check the power steering reservoir a few times before you fire the truck up in the morning. One on a cold morning and again on a warm morning, you'll be able to see a difference even in such a small amount of fluid. Now imagine how much difference there would be in ~13 qts of ATF vs ~1 qt.

And as far as picking a specific temp range, I think thats really the only way. This system is not thermostat controlled like engine coolant is. So the actual trans temp will vary wildly based on ambient, driving conditions, idle time, etc.

 

That’s interesting about the lack of temp control on the tranny, that does explain things, but I still wonder why not pick a cold temp instead around room temp so no startup is required at all.

 

I shouldn't speak in absolutes, Im not an expert. But Ive never heard of a thermostat on the 2nd gen trucks. Vs the 3rd gens which apparently do have one somewhere.

And as far as 'cold', how do you define that? Im quite sure your cold down in NC is not the same as my cold here in Maine All in all this system is probably the best all around, though maybe not the easiest

 

I’m going off of a previous post here theorizing that the procedure was only ever meant to be done in a shop…so cold temp would be relatively consistent indoors…ish

 

Actually nobody has ever tried it. Must've been a dream you had lol. If you're talking about people using an IR gun and measuring the pan temp, that's not even close. Nobody and I mean no one has tried it with a scangauge, ultragauge, or torque pro or any other app to actually confirm exactly when the AT check light comes on and shuts off. How do I know, because you need to jumper the OBD port to do the AT check sequence. And all those gauges use a connector to plug into the OBD port and that connector needs to be unplugged to jumper the OBD port. I've figured out a way to do it without the jumper. That's how I know it's never been done on TW. Good day now!

 

A shop in TX might not be much less than 95* on many days, and the vehicles are sitting in the sun in a parking lot until they get brought inside either way

The jumper gets disconnected after the A/T light flashes when entering check mode, you don't have to leave it in. I tried this with both the 4runner forum's custom formulas many years ago to verify them, and wasn't the first. All good though, it's not a competition...

 

The range for fill check is currently 20 degrees, seems pretty reasonable to theoretically find a 20 degree range that covers room temperature scenarios. Maybe there was some other logic.

Not sure how being in the sunlight significantly impacts the temp of a component that’s on the underside of the truck.

 

But have you posted about it on here and showed the results of your findings? Because I can say the same thing about anything else too. Like "Oh yea I've done that before back in the days I use to be a millionaire and flew a helicopter over hawaii with a supermodel on my lap". lol. Not trying to be a jerk, just saying, I tried searching and haven't found anything. Everyone just seems to use spec sheets and FSM manuals that point to what the temp range "should" be, but nobody has tested it to be for certain.

 

You are a 100 % wrong. I confirmed it with my fusion app after I jumped my obd.

 

You didn’t say “I’ve never seen a way to do it posted here on the forum”, you said “no one’s ever done it” which was a bit preposterous to say when speaking individually for all of mankind. Then you were almost instantly owned. The best approach would have been “oops I was wrong, thanks for the info”.