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Changing overdue transmission fluid

my friend has a toyota rav4 with 70k miles. the transmission fluid has never been changed. she has been told that she should not change it because if she does, she will ruin the transmission. varnish, dirt and other materials will be loosened. should she change the fluid or not?

That myth about changing transmission fluid is just that, a myth.

What often happens is someone with 150,000 miles on a transmission will see a problem of some sort and decide to change the fluid (for the first time). Well not too surprising it often does not work and the transmission soon fails. It likely would have failed a few days earlier if it had not been changed. It was not the change that caused the failure, but the failure to have changed it two or three times before that.

Frankly 70,000 is not all that long for transmission fluid. I would like to see it changed at maybe 40,000, but she should change it now. Not changing it is far more likely to cause a problem.

However tell her to avoid a "flush" job.  The proper change, especially with this many miles would be to drain, remove the pan and clean the filter and pan, then re-assemble and re-fill.  Your friend should have many more miles without a problem.

I agree with Joe with every aspect. Except one.

Most people are afraid of the “FLUSH” word. But these machines are not flush machines. Instead, they’re fluid “EXCHANGE” machines. This means you connect a device into the loop of the system that exchanges the old fluid with new fluid. And doing this replaces 100% of the fluid. So, if anyone can explain how this is detrimental to the system, I’d like to hear it.

Look at it like this. How would you feel if you brough your car in for an oil change? And you were told that they only drained 25% of the oil and replaced the oil filer? Would you call that an oil change? It’s the same when doing a fluid change on a tranny.


I agree. I think that some on this board don’t understand how this process works.

The detrimental thing about the flushes is the “Human” factor. Trying to make the almighty quick buck by not first dropping the pan (Where applicable) and changing the filter and examining the pan’s debris. This is why a lot of people walk through my door after letting some shop “Flush” their trans. If I had my way, only certified transmission shops would be allowed to purchase such machines.


JMHO, but I think transmission fluid should be changed roughly every 30k miles or so. Early, regular fluid changes can do a lot in preventing a premature transmission failure.
Unfortunately, many people never do it at all, wait until the transmission is showing some symptoms, and then change or flush the fluid in hopes it will be a cure-all.

Some years back a cousin of mine had a trans fluid flush done on his Pontiac while thinking this would cure a slight shifting glitch he was experiencing. The problem remained and when I dropped the pan on it I discovered the filter was about half clogged and the pan was absolutely filthy.
Cleaning it all out and installing a new filter/fluid at least got it shifting right again and he at least got another couple of years of use before the trans finally gave up.
So I agree; the pan needs to come off. It’s also a good way of detecting a major problem early.

To me, not changing the transmission filter is equivalent to changing the engine oil and not the filter or swapping a fuel pump out while leaving the old strainer and filter in place.

I don't have anything against the "Flush" except that it misses dropping the pan and doing the filter, at least in most cases.

Similar situation with a 1993 Toyota Camry with 121K miles .

I am thinking about dropping the and changine the filter ( screen) . I would the the refilling and do a flush through the cooler line . Would this be OK ?

Normally I agree with tester on just about everything, except this topic. Whether you call it a flush or an exchange, it doesn’t get 100% of the fluid unless the pan is dropped. Even then it still won’t get 100% of the fluid, but more than without dropping the pan.

The pan is a reservoir. When you suck the fluid out of one side of the pan and add it to the other, you only dilute the fluid in the pan. Its no different than doing multiple changes of transmission fluid.

I would recommend that your friend do a fluid drain and refill now and again at 90k, then every 30k after that. Be sure to use only the Toyota T-4 transmission fluid.

FYI, Toyota uses a stainless steel screen as a filter. It is easily cleaned out as good as new, it is also very expensive to replace. Other than that, I agree that the pan should be dropped and cleaned and a new gasket installed. The filter should be flushed with a clean solvent and can be reused.

Should be.