Automatic Transmission Flush or just drain and replace filter?

I just turned 60K on my 02’ Nissan Maxima and want to replace my tranny fluid. I am considering having the tranny flushed, but people are telling me it is better just to drain the fluid and replace the filter. I bought this car with 40K on it and do not know if the trannmission was ever replaced. The flush is supposed to replace all the fluid, remove varnish while the drain process will leave some of the old fluid. What are your thoughts?

Simple answer…Drain…never flush transmission…

Why do you say “never flush”?

From all the previous posts on this subject I have learned that flushing is never advised, is a money maker for the station and it stirs up residue and junk that can cause problems in the future…

I disagree with the recommendation to simply drain and replace the filter as this will allow 1/3 of the old fluid volume to remain in the torque converter. I know that a flush will cost more but this will allow a more thorough replacement of all of your tranny fluid. I’d also recommend that you look in your owner’s manual or check with Nissan and only use what they specify. The biggest mistake you could make is allowing one of these ‘specialists’ to put in whatever it is that they think ‘should work’. Good luck with your choice.

Automatic transmission maintenance intervals are given in your owner’s manual. Follow them, and also make sure you realize that “severe” conditions are what most of us drive in city traffic. The general intervals are designed to refresh the conditioners and detergents in the oil, and replace most of the oil which has thickened from heat with new oil. This also, of course, removes sediment when the pan is removed and cleaned and the filter is replaced.

Assuming that 1/3 of the oil remains in the torque converter (I think that is a bit high, and some cars have a TC drain plug), the sediment is still trapped in the filter and pan. Routine service intervals will maintain a healthy level of good oil in the transmission and help clean any deposits that may have formed. Most transmissions that have been regularly serviced show no deposits for this reason.

Flushing is a money maker for shops. Either they advertise that they “flush” the transmission and simply service it with new oil and filter, or they use a strong detergent to dissolve residue, mainly in the valve body. But since they use something other than transmission oil to flush (if they do so), then 1/3 of your transmission might be filled with detergent, not oil, when the thing is buttoned up. Or if they flush with tranny fluid, what’s the point? If it really needs “flushing” due to a driveability problem, then make several short interval services, say 5,000 mile intervals or every oil change, and see if the fresh oil will loosen things up. If not, you probably need a valve body overhaul before things get really out of hand.

Since you don’t know the history of the car, I would simply follow normal service intervals unless you are having problems with the transmission. That should be more than enough to keep you out of trouble. If it ain’t broke …

Just change the fluid in the pan and the filter. As long as you do this at regular intervals, say 20-30k you will be fine. There really is no need to flush.

Read the owner’s manual. I’ll be surprised if you find the word “flush” anywhere near the word “transmission.” The only thing I recommend flushing is the cooling system. The manufacturers know that about 1/3 of the transmission fluid remains in the transmission during a standard change, and they still recommend a standard fluid change. There are too many horror stories about transmissions failing shortly after being flushed. Why gamble? Stick with the tried-and-true method.

I would stay away from the flush. Drain and refill every 25k for normal service.


Have a 92 Cherokee @ 95k, wifes car, 90 olds (3800eng) @ 135k, had both flushed & filters & fluid replaced. We run can of B&G tran. cleaner prior to complete flushing, draining changing filters and buttoning them back up. Had to re-tork trn. pan bolts at 5k. Not another thing been a problem. Have 110k on the Jeep, 156k on the olds. A brand new flushing machine was used & you should have seen the black stuff coming out in the clear recovery line. For what ever its worth. Cost $150.00 both cars!

Black Stuff = Seals, gaskets, and clutches being eaten up by the flush detergents.

The best way to do a flush is to change the oil couple of times with a short interval.

Owner manuals often say to “service” the auto trans. In this day and age, that often means to hook the cooler lines up to a machine that exchanges most of of the fluid. This might or might not be called a flush. I would get the details of what flush means in this case and get the details of what is the recommended procedure for this vehicle.

Isn’t great to live in a free society and have the privilege to make dececions based on educated & uneducated experiences. At 63 years & some days, had MANY cars, I’ve been fortunate with most. Preowned with good maintance but not necassaril perfect.:slight_smile:

Transmissions have filters that need to be cleaned or replaced. To do that, the pan must be removed. Some shops do both, remove the pan, change the filter, then “flush” it. The cooling lines are not big enough to to allow a high enough flow rate to “flush” anything. It’s just an easy way to change the oil trapped in the converter…It’s by no means 100% effective. The vast majority of cars NEVER have their transmissions serviced…

IMHO, just have the fluid and filter replaced every 30K miles, or so (whatever the recommended interval is for your car). You should not need to do anything else if you change the fluid/filter at the appropriate intervals. There are horror stories of folks having transmissions flushed after being neglected for many miles, but I don’t have any first hand experience.

They’ll never get me to believe that a flush replaces all the fluid. I think it filters a lot of your old fluid and replaces some of it. If they even do the flush. I’d rather pay less for somebody to fake draining and refilling than to fake flushing. I think that it is more likely to get the basic drain actually done anyway. That was my worst case scenario briefing. Some people never change the fluid and some transmissions quit after a flush or a change. I only recommend a flush if the manufacturer does, or builds a transmission without the possibility of just draining it, as some now do.