Hi all,

Something that I saw with the SC4 that carried over to the GS4 was this - the advice that says, when you change your transmission fluid, you should NOT drain it fully, but instead let the fluid in the pan out (~2qts), change the filter, run it for ~5k miles, and repeat until you've replaced the entire volume of the system with new fluid (mostly, since the old and new fluids mix). Perhaps I'm getting my posts confused, but if this information is correct - why? A couple friends who work as techs at various places told me this is weird, and that they've never heard of it. Perhaps it's a Lexus/Toyota-specific thing.

Thanks!

 

The only place I have ever heard similar advice has been on the internet - the theory is something like you are flushing out the converter. Everyone I know drains out as much as possible and then refills. And those that are overly worried about it then repeat the process in a few days or weeks.

YMMV and I'm sure you will get differing opinions.

 

Don’t open the pan and mess with the filter. Not necessary, and I have seen FAR more trans ruined from mistakes here, than helped.

You can do little incremental changes like that, diluting the effectiveness like that. It is akin to changing only one quart of engine oil every 1k miles. If that sounds like a good use of time and effort to some people, I don’t get it. If you wanna do any good change more fluid.

 

Read and follow owners manual from Lexus. IGNORE everything else.....

 

This is terrible advice. The owner’s manual has no useful information regarding this issue. And what Lexus does usually give via dealers, etc., re: transmission service is notoriously inconsistent and also often very bad.

The manufacturer of the transmission is a much more reliable source. They say maintain it. Not listening to them, and listening to Toyota/Lexus, would be a mistake IMO.

 

That’s about the least efficient way to change your transmission fluid. The pan actually holds about 4qts, which is about the total amount. So I guess if you want to drain the pan and then refill it, then drive the car, then do it again you would probably change about 65% of the ATF. Not much better than just draining the pan, refilling it and then calling it a day. The better method is to remove one the tranny cooler lines, putting it in a jug, starting the car and letting it cycle the old fluid out while adding new fluid to through the dipstick and just draining 8qrts while adding the same amount. This would ensure that you change virtually all the ATF,

 

By far the best way. I don’t mind doing a simple drain/fill periodically once I’ve got a complete clean fill. But if an original fill has been left in 100k miles or more, this is the way to get a clean baseline fill.

 

And the fluid is the only thing you need to deal with on these transmissions. Make sure to use the recommended, Toyota, ATF and make sure it’s at the proper level and a nice garnet red color and your transmission should be fine. If it turns brown or starts smelling burnt then you need to change it. There is a drain plug if you just want to change half every 30k? That would be fine. You don’t drop the pan or change the filter or any thing like that. These transmissions are more likely to fail from being serviced with the wrong fluid than complete neglect.

 

Thank you all very much for the replies! This information is very helpful. I thought that tidbit had seemed counterintuitive, but I didn't have the experience to say otherwise. I will set about doing the first 4qt drain-fill soon.

Of course - ONLY the correct Toyota Type-IV ATF. NEVER anything else. I do remember that point being emphasized ad nauseam, and that part did make sense.

 

Agreed with the others. These transmission do not have a real filter, just a pick up screen. So no need to pull the pan unless its leaking. In my experience you will only be able to drain out around 4 quarts. Just do this periodically until you see clean red fluid on your dipstick checks.

 

Yeah, the staged drain-and-fill is more of a cautious Toyota/Lexus thing. Idea is you don’t shock the trans with 100% fresh fluid all at once. Some people swear by it, others just do a full swap with no problems.

 

As a new owner of a GS300, I've watched a lot of videos on this and went to two different dealerships for their evaluation. One dealership said it should be done every 30K miles if you've been changing it. And since I'm at 130K miles and it was done at 90K miles, I should do it. The other dealership looked at it and said I was fine because the color was still red. Some videos I've watched said the color means nothing and it's more about the grit or particles in there (if any). And another video I've watched said if your fluid has never been changed, don't touch it at all because disturbing it could do more damage than helping it.

I'm the furthest from an expert and have not even done the drain and refill myself out of fear of messing it up. I know it's hard to mess up because all you do is put a measuring bucket under the car and open the bolt and then refill via the dipstick but I'm pretty car illiterate.

 

Honestly, for normal people like us who don't do transmission rebuilds for fun, the information is scattered and based largely on hearsay.
My take is that a normal drain and fill isn't just fine, but is actually preferred unless there's something wrong with your transmission fluid (ex. metal shards, literally black, contaminated, stuff like that). The idea is that transmission fluid is a hydraulic fluid, not just a lubricant, and thus it's the fluid that's being used to physically move things around. It's also, as you may know if you've ever let bolts soak in it overnight, a fairly effective solvent, which means it can dislodge built-up sludge that can get stuck in places like the valve body.
Generally, this means that new transmission fluid being diluted by the old transmission fluid actually isn't a bad thing. Being overly aggressive with trying to get perfectly bright red transmission fluid could result in you dislodging some build-up and having it end up somewhere it's not supposed to. Not only that, but you're also changing the viscosity, which could result in better shifting, or it could reveal existing problems that were being masked by the higher viscosity of the old fluid. Many people mistake that second option for the flush being what did it in.
It's basically the same reason a lot of people don't like running engine flushes.

Transmission fluid needs to be "broken in", and it's the only regular fluid in your vehicle that needs this. The viscosity of transmission fluid doesn't just change due to burning and contamination, the changing viscosity is actually a built-in function of the fluid. After so many miles, the fluid will "shear" to a certain degree, and this is unavoidable. What engineers have done is basically make this a feature instead of a bug of the transmission fluid, and purposefully engineer it to go in at a different viscosity than it's rated to run at. The mechanical stress of running will "shear" it, and it'll settle into its rated viscosity.
This is a double-edged sword - It's a measure against shearing in a way that reduces functionality, and Toyota T-IV, the fluid that goes in your transmission, is known to shear fairly significantly. Eventually, it'll be sheared to a point where it goes out of its rated spec, and it'll be less efficient. Thus, new transmission fluid is needed to make sure your transmission is running correctly.
The theory here, and I'm not an engineer, is that mixing the old and new fluid will basically keep it running at the viscosity your transmission is expecting, while changing it all at once will significantly change the viscosity and potentially overwork it. Think of it as going straight from a cold pool to a hot tub.

This advice is mostly only for higher milage cars where you don't know when the last transmission service was. For cars under 100k miles, or cars where you absolutely for certain know the fluid has been changed on a schedule, well, the fluid just shouldn't be dirty or burnt enough to justify wanting to spend all the extra time, money, and effort getting perfectly red fluid.
Transmission fluid is not engine oil. It doesn't get the same level of contaminates, it's a solvent, and it pulls triple-duty as a hydraulic fluid, a lubricant, and cooling. There's a whole lot going on there, and basically 0 good ways to actually see what's happening without being one of those guys who rebuilds transmissions for fun. As satisfying as it is to get bright red fluid and say your transmission is like-new, it's just not really worth it in basically any scenario other than severely neglected fluid.

When it comes to the "Take the hoses off and let them drain into a pan" method, I generally only do this in case of an emergency - When the contamination is so bad that the car absolutely cannot be driven until it's dealt with. This is generally in cases of the strawberry milkshake of death, instances where the transmission fluid has mixed with coolant in the radiator, and there's a good chance I may have to replace the fluid pump anyways. The reason I only do this in severe scenarios is because you're overworking the fluid pump by doing this method. Think about taking the coolant hoses off your radiator and running the car until the engine block is dry - Even if the engine doesn't overheat, you'd definitely worry about damage to your water pump, no? Same idea here.

That's my two cents on the issue as someone who's had to rescue a few transmissions from an early demise due to contamination or improper maintenance. Take it with a grain of salt, I'm gonna be honest, I have very little idea what's actually happening inside of a transmission compared to how much I know about engines. They're scary black boxes that grenade your car if they get an attitude, so I generally stick with what the safest, gentlest options are. That's just me.

 

You sound very well versed than a normal person who don't do transmission rebuilds for fun. I've never swapped out the fluids. I'm interested in a very thorough video on how to do it. If you or anyone can link any, it would be very much appreciated because it sounds straight forward and I don't want to pay $200 for something I can do myself, if possible for the cost of the fluid itself. THANKS!!!

 

How patient are you? I'm likely gonna record a video on specifically how to do it on the 2GS within the next couple weeks, since I was gonna do it while I'm doing timing, and I'm already recording that job.