I just got a 98 Mazda 626 2L and need to flush the atx fluid, it's really dirty brownish red, but not burnt and I didn't notice any particles in it.

I think the car has a CD4E tranny ( it turns out to be a GF4A-EL actually, but I don't think that matters ), and I've heard they have internal filters which can't be changed without dropping and disassembling the tranny.

I came across this procedure for flushing the fluid, and wanted to know if it's safe. I'm worried that running the transmission with the inlet line disconnect could damage something due to lack of lubrication.

Tools required: pliers, 10mm socket, milk jug, transmission fluid funnel

Parts required: 1 case of MERCON transmission fluid

Optional: get a new 1/2" screw-down hose clamp to replace the cheap factory hose clamp.

  • Drive car up on ramps.
  • Remove the drivers-side black plastic underbelly pan (held on with several 10mm bolts). This exposes the 2 hoses running to the transmission from the transmission cooler.
  • There are 2 black rubber hoses running from the external transmission cooler in the front of the car. Each one attaches to a metal tube that attaches to fittings on the transmission.
    • The tube attached to the front of the transmission is the outlet (i.e. fluid is discharged from the transmission here).
    • The fitting in the rear of the transmission (and also closest to the front wheel) is the inlet (i.e. fluid enters the transmission here).
  • To flush the transmission and the external cooler, you need to disconnect the rubber hose from the metal pipe that connects to the rear of the transmission (the inlet).
  • Identify the transmission inlet hose, and remove the hose clamp with pliers.
  • Pull the rubber hose off of the metal pipe. Some fluid may come out, but there won't be much.
  • The idea of a transmission fluid flush is to use the transmission's own pump to pump out old fluid, and then replace it with new fluid. I used a 1-gallon milk jug to collect the old fluid, and a helper to start and stop the car's engine on my command.
  • Position milk jug under disconnected inlet hose, and have helper start engine. Fluid will pour out of the inlet hose into the milk jug. Stop the engine when approx 2 quarts have come out (the milk jug is 1/2 full). This will take 15-20 seconds or so.
  • Add 2 quarts of new transmission fluid into the dipstick tube.
  • Repeat steps 4 and 5 until the transmission fluid coming out is the same color as the new fluid. For me, it took a full case (12 quarts) of fluid. At least one time during step 4, have the helper shift the transmission into R and D while the engine is running.
  • When all fluid has been replaced, reconnect the rubber hose onto the metal pipe and install a new screw-type hose clamp (the factory clamps are junk).

EDIT 2/1/2016

I was thinking that I could connect a second hose to the other side and while old fluid is draining, stick the second hose in a jug of new fluid and let it be sucked up while the old fluid is draining out.

If I want to drop the pan and change the filter, how would I modify this procedure so that I don't waste too much fluid?

  • If you want to change the filter, I'd suggest you do that first before attempting any of the fluid exchange stuff. The only difference would be, once you have a dry pan with new filter, put the 2 quarts back into the tranny and start from that point with exchanging fluid. Jan 2, 2016 at 22:31
  • @robertsbarnes If your good with this response, I'll award the bounty. Jan 5, 2016 at 2:05

1 Answer 1


This is an excellent procedure that will cause no damage. We have used several versions of it for years with no ill effects. For most transmissions draining only removes 1/2 to 1/3 of the total volume. It does not hurt anything for two reasons:

1 The trans is under no load. The clutches have no torque load applied so they have no reason to slip.

2 Lubrication is never really lost. There is not sufficient time for the fluid to drain off the parts.

We add another step; we run the shifter through the available gear ranges to flush the clutches that are not supplied fluid when the shifter is in Park. Do not do this unless the drive wheels are securely up off the road. We have the vehicle on a hoist when we do it.

Alternate method 1: Fill while run method. You can skip the step to fill step and just add to the filler while the engine is running.

Alternate method 2: Drain, fill and drive method. This involves a drive of a few minutes between drain and fill events. This method ensures that the dirty fluid is flushed out of all the passages and clutches for all the gears.

The stock hose clamps are better than gear clamps. If the connections are leaking it is because the hoses hardened too much and need to be replaced.

  • I was actually thinking of just taking a second hose and hooking it up on the other side and sticking it in a full bottle of new fluid so it could suck up new fluid while the old fluid is being pumped out. I finally figured out that my model has a GF4A-EL tranny, although I don't think that really matters. Jan 2, 2016 at 17:45
  • If I want to drop the pan and change the filter, how would I modify this procedure so that I don't waste too much fluid? Jan 2, 2016 at 18:31
  • @RobertS.Barnes It will not make much difference. The first drain is done when the pan is pulled but you do not get much more fluid out than draining with the plug. But you do get any filters changed, magnets cleaned and a check for chunks. I use less fluid when I use the drain and drive method because it mixes better. Jan 3, 2016 at 6:15
  • Well, I changed the fluid today. Apparently, I didn't fill enough before trying to cycle through the gears, cause I got this horrible scary noise after a second so I shoved it back into park and killed the engine. Once I finished the process though everything seemed OK, Took it for a little drive around the parking lot and everything seemed to be working alright. Jan 6, 2016 at 15:49
  • The most common cause of a loud noise while shifting with the wheels off the ground is failure to get the wheels fully stopped before shifting back to park. The park lock can only engage when the wheels are stopped; if you try it rattles really loud. Jan 6, 2016 at 16:50

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