Transmission Oil

Does it do any good to change the automatic transmission oil without flushing the torque converter?

The question should be…Does it do any good to change the automatic transmission oil without dropping the pan? The stories they tell you about flushing are garbage.

Nothing gets rid of all the old fluid. A little new fluid will cause stuff to come out of the TC for several months. If you can stand the mess, it is better to do about 4 pan drops over 6 months. The pump out method works pretty good if you drop the pan again at 6 months.

For most people, changing fluid is just fooling themselves. If you want to extend transmission life get an external cooler. New fluid does not extend the life of the transmission, lowering seal temperature does! I clean out my system, add a cooler, and drive another 100K on the same fluid which stays nice.

Sure. It will do more good to change the fluid by dropping the pan, changing the filter and the fluid. Flushing is not usually a bad idea, but it is usually a better idea to get the filter changed than to worry about what % of the fluid is changed.

Of course the most important thing is to get it changed before you are having transmission problems. It seems most people wait until they are having problems then they change or flush it and end up with the transmission crashing shortly after. Of course it would have anyway.

So do get it change one way or another, but I would suggest not flushing and dropping the pan and changing the filter as well.

I disagree with the Opera House’s statement that changing the fluid will not extend the life of a transmission. Changing at REGULAR INTERVALS will definitely lengthen the life of your tranny. Perhaps what OH meant to say is that once the transmission is damaged by old fluid, changing it will not extend its life.

An external cooler in addition to the one already in your radiator is not a bad idea.

Changing the fluid and filter at regular intervals will certainly extend the life of your transmission (I like 30K miles). If your car needs an external cooler due to it’s service you should add one, in most cases the stock cooler is adequate.

I don’t know what car we are talking about, but does it have provisions to drain (not flush) the TC?

Stock cooler is almost never adequate. Some transmissions will benefit from replacement of friction modifiers damaged by heat. Original fluid should last the life of the vehicle if kept from overheating. Most transmission damage is from aging seals. Fluid change is a big myth.

I really don’t understand the logic of trying to re-engineer the car to avoid a little routine maintenance. There is no chance that the original fluid will last the life of the vehicle, unless that life is very short. My car now has 417,000 miles/26 years, do you seriously thing I should be running the original fluid?

You should do whatever you like, but please do not post incorrect information. Someone might make the very expensive mistake of believing you. Stating “Fluid change is a big myth” is dangerous misinformation.

BigD, follow the owners manual requirements for fluid changes as a minimum.

Transmission fluid is just 10W oil with the proper additive packages. And as with motor oil, the transmission fluid additives break down and the fluid becomes oxidized. Since the torque converter can hold up to 70% of the fluid that’s held within the transmission and it’s not changed, adding fresh fluid just gets contaminated from the old fluid still held in the transmission.

Or think of it like this. How would you feel if you brought your car in for an oil and filter change, but they told you they changed the filter but only drained 30% of the old oil out and added enough fresh oil to bring the oil to the proper level. Would you call that an oil change? It ain’t in my book.


Again, I don’t know what type of car the OP has. On mine, you can (and should) drain the torque converter when you change the fluid/filter.

New fluid is like going against Mom and apple pie, but if your fluid is dark and smells the oil is overheating. Overheated seals leak. Leaking causes pressure loss and slow shifts. That causes burning clutches. All other failures are just poor manufacturing. Changing fluid just masks the problem and doesn’t prevent continued seal damage . Fluid has almost nothing to do with extending life. I got into rebuilding transmissions as a hobby, even my dentist rebuilds them, and spent my life in industry in failure analysis. Look at the new home air conditioning systems. They all had to come up to new E Star ratings. They all did this with very little effort beyond increasing the size of the heat transfer coils. The averages are with the manufacturers that most vehicles will get 140K with a smaller heat transfer and less fluid. What I am saying is if you only have $100 to spend on a transmission for as long as you own your vehicle, it is best spent on a transmission cooler and not fluid changes.

BigD; as I said, follow the owners manual requirements for fluid changes as a minimum.

Yes, the additives in the fluid break down and what’s the filter for? You can’t just assume it will never clog, most cars anyway. Dropping the pan allows the tech to clean out the normally ocurring aluminum shavings and to eyeball and possibly nip in the bud develpoing problems. Off the subject, but does your usermame have anything to do with the Mile-high city- Denver, Colorado, capital of the Centennial State?

It does, I was born and raised in Denver.

I researched the issue of changing the transmission fluid recently and came away totally confused. Many say to never change the fluid if the car has a lot of miles and it has never been changed. It will loosen particles and could cause the transmission to fail. Others say to change it regularily. Flushing was not recommended for any car.

Not changing the fluid in a transmission that has never had it changed is an old spouses’ tale. The anecdotal reports of transmission failure soon thereafter don’t account for the likelihood that the transmission was already on its way out from lack of maintenance and the fluid was changed as a last gasp to salvage it.

Karl’s take on the need for periodic fluid and filter replacement is correct, IMHO.

Yes, it does. You should change the transmission oil as often as your owner’s manual recommends using the method it recommends, and even though draining and refilling doesn’t get it all out, that may be all your owner’s manual calls for. If your transmission needs flushed or to have the pan dropped and filter changed, it will say so in your owner’s manual on the maintenance schedule. If you are looking to save money, you could combine techniques. For example, you can drain and refill at 30,000 miles and to a complete fluid flush at 60,000 miles. Then at 90,000 miles you can have the pan dropped and the filter changed. Then start over again with a drain and refill at 120,000 miles and continue the cycle. This might be useful if your owner’s manual only calls for you to drain and refill every 30,000 miles. It might actually extend the life of your transmission.

The people who say to never change the fluid are the same ones who only go to a doctor after they have a heart attack. I never heave understood that reasoning.

I’ll only address the part from OHW about not changing the fluid. Of course it should be changed on a regular basis and of course the fluid and additives breaks down over time.
If memory serves me correctly, OHW is also the one who claims that changing a dirty air filter is also a myth and cars will will be just fine with a filthy one.

The only correct part is the bit about adding an aftermarket fluid cooler.

I was born in Aurora but have spent 95% of my life in Pennsy. I root for Philly sports teams first but Denver’s not far behind. Oh well, small world.

Thanks, NYBo. Another old wive’s tale is the one where someone neglects to change their engine oil for like 30,000 miles; changes it, and the engine goes. Untill someone does a real good survey with a random sampling I won’t believe the last oil change did in the motor.

I’s nice to know I am remembered…And I change my air filter every 100K whether or needs it or not!