DIY TRANNY FLUSH

A forum for the legendary Nissan Pathfinder and Infiniti QX4.
PATHFINDER99NI
Posts: 90
Joined: Fri Mar 30, 2018 8:47 pm
Car: 1999 Nissan Pathfinder LE 4x4

Post

Guys, my tranny has been on my mind lately. It’s getting ready to hit 260k mi’s and I don’t remember the last time the fluid was changed.

The only thing that’s stopping me is, I’ve read that in these instances, a transmission failure is seen sooner. Something to the effect of, “the transmission begins to rely on the grit in the fluid not to slip”.

What’s your guys opinion? What setup did you use?


User avatar
VStar650CL
Technical Expert
Posts: 8291
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

How nasty is the fluid? If it's brown and full of clutch material then fresh fluid with fresh detergent could cause big problems. We call that "ATF soup" and it's hopeless, just leave it alone till something breaks. If it's still reddish and reasonably transparent, then a spill-and-fill should be beneficial.

PATHFINDER99NI
Posts: 90
Joined: Fri Mar 30, 2018 8:47 pm
Car: 1999 Nissan Pathfinder LE 4x4

Post

VStar650CL wrote:
Sun Aug 14, 2022 7:14 am
How nasty is the fluid? If it's brown and full of clutch material then fresh fluid with fresh detergent could cause big problems. We call that "ATF soup" and it's hopeless, just leave it alone till something breaks. If it's still reddish and reasonably transparent, then a spill-and-fill should be beneficial.
I haven’t looked, but I’m guessing it’s around brown and soupy looking.

Mike W.
Posts: 386
Joined: Tue Jun 13, 2017 6:59 pm
Car: 2003 Infiniti QX4 with a drinking problem. Gas and oil.
2002 BMW 525it
1998 BMW 328is
Location: California Whine Country

Post

#1. Nobody, besides those selling it, seem to recommend flushes.

#2. It might make you cringe, but fluid change is good, even high miles. Grit, which is what overused ATF has in it, does not promote correct friction characteristics between the clutch plates. Think about this, the tranny was designed to have clutch plates with friction material on them to interact with either the same or plain steel plates, with clean fluid. If you throw sand in there (grit, wear components) it's not going to act right.

User avatar
VStar650CL
Technical Expert
Posts: 8291
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

Mike W. wrote:
Sun Aug 14, 2022 7:54 pm
#2. It might make you cringe, but fluid change is good, even high miles. Grit, which is what overused ATF has in it, does not promote correct friction characteristics between the clutch plates. Think about this, the tranny was designed to have clutch plates with friction material on them to interact with either the same or plain steel plates, with clean fluid. If you throw sand in there (grit, wear components) it's not going to act right.
That's right as far as it goes, but the problem isn't with the bands and clutches, it's with the valving. All tranny fluids have high detergency, and changing the fluid on a soupy trans has the same effect on the VB that flushing a sludge motor has on engine seals. Dirt was holding the seals together and suddenly they all leak. Except, when a trans valve leaks internally, it doesn't show up on the garage floor, it shows up in a tranny that quits moving. That said, there's a big difference between just "burned-and-brown" and soupy. Brown fluid should be changed, brown and opaque fluid should be left alone. The OP should really take a look and not assume anything.

PATHFINDER99NI
Posts: 90
Joined: Fri Mar 30, 2018 8:47 pm
Car: 1999 Nissan Pathfinder LE 4x4

Post

Mike W. wrote:
Sun Aug 14, 2022 7:54 pm
#1. Nobody, besides those selling it, seem to recommend flushes.

#2. It might make you cringe, but fluid change is good, even high miles. Grit, which is what overused ATF has in it, does not promote correct friction characteristics between the clutch plates. Think about this, the tranny was designed to have clutch plates with friction material on them to interact with either the same or plain steel plates, with clean fluid. If you throw sand in there (grit, wear components) it's not going to act right.
I don’t plant to buy any cleaners, I just want to flush out the old ATF w new ATF. If I just do that, would the tranny be ok?

Mike W.
Posts: 386
Joined: Tue Jun 13, 2017 6:59 pm
Car: 2003 Infiniti QX4 with a drinking problem. Gas and oil.
2002 BMW 525it
1998 BMW 328is
Location: California Whine Country

Post

We may be into semantics here, but I do not recommend a flush. I do however suggest one or more drain and refills. Do that and the tranny should be ok, but I can't guaranty anything. More than likely if it fails it would have anyway. Once you've been into them, and I have, you see why clean fluid is so important.

User avatar
VStar650CL
Technical Expert
Posts: 8291
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

PATHFINDER99NI wrote:
Mon Aug 15, 2022 5:39 am
I don’t plant to buy any cleaners, I just want to flush out the old ATF w new ATF. If I just do that, would the tranny be ok?
New ATF is highly detergent and highly solvent. With a crappy trans, you take your chances. :gotme
Mike W. wrote:
Mon Aug 15, 2022 9:59 am
We may be into semantics here, but I do not recommend a flush.
Agreed. Flushing is pretty uniformly a bad idea. :nono:

PATHFINDER99NI
Posts: 90
Joined: Fri Mar 30, 2018 8:47 pm
Car: 1999 Nissan Pathfinder LE 4x4

Post

VStar650CL wrote:
Sun Aug 14, 2022 7:14 am
How nasty is the fluid? If it's brown and full of clutch material then fresh fluid with fresh detergent could cause big problems. We call that "ATF soup" and it's hopeless, just leave it alone till something breaks. If it's still reddish and reasonably transparent, then a spill-and-fill should be beneficial.
Ok, I just checked and the fluid is a CLEAR reddish brown. I was absolutely surprised for how long it’s been and as hard as I drive it.

So I guess it’s time for a flush.

User avatar
VStar650CL
Technical Expert
Posts: 8291
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

PATHFINDER99NI wrote:
Sun Aug 21, 2022 11:27 am
Ok, I just checked and the fluid is a CLEAR reddish brown. I was absolutely surprised for how long it’s been and as hard as I drive it.

So I guess it’s time for a flush.
Clear is good, still-reddish is even better. Just spill-and-fill and change the filter, don't flush. Back-flushing dislodges whatever crud is in there and puts some of it back in circulation, forward-flushing using the trans cooler lines is healthier but can still cavitate the front pump and cause problems. Trust me and Mike on this, flushing is bad.

PATHFINDER99NI
Posts: 90
Joined: Fri Mar 30, 2018 8:47 pm
Car: 1999 Nissan Pathfinder LE 4x4

Post

VStar650CL wrote:
Sun Aug 21, 2022 11:38 am
PATHFINDER99NI wrote:
Sun Aug 21, 2022 11:27 am
Ok, I just checked and the fluid is a CLEAR reddish brown. I was absolutely surprised for how long it’s been and as hard as I drive it.

So I guess it’s time for a flush.
Clear is good, still-reddish is even better. Just spill-and-fill and change the filter, don't flush. Back-flushing dislodges whatever crud is in there and puts some of it back in circulation, forward-flushing using the trans cooler lines is healthier but can still cavitate the front pump and cause problems. Trust me and Mike on this, flushing is bad.
Yes, by flushing, I meant that I’d attach a reservoir of clean ATF (just ATF, no additional detergent) to one cooler line and then attach the other to a clear hose emptying into a bucket. You’re saying not to do this?

User avatar
VStar650CL
Technical Expert
Posts: 8291
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

Post

Done very carefully it's fine, but don't let it run dry or bubble, that's when you'll cavitate the pump. It doesn't sound like your fluid is in rough shape, and you'll definitely want to drop the pan and change the screen anyway. That will void all but about 3 quarts in the TC, so I kind of don't see the point.

bamashooter
Posts: 1
Joined: Sun Apr 17, 2022 7:13 am
Car: 1987 Nissan Pathfinder XE V6

Post

I was always flushing was acceptable if doing so from day 1, not miles and years only. Reportedly, flushing years of potential grime, as tiny as the particulate might be, can get caught up in the assorted small valves, orifices, etc. No idea on vehicles of the pas few decades, however, very few torque converters had drain plugs. Believe Chrysler products did. Many tranny pans had no drain plugs. Had to begin dropping the pan to drain the fluid. Folks would have them drilled and tapped for a plug. Depending on the TC, they can hold a proportionally-large amount of fluid which doesn't come out with a typical fluid change. BOTH, I've seen very few failures when not used under very harsh conditions and regular fluid changes.


Return to “Nissan Pathfinder Forum / Infiniti QX4 Forum”