which Automatic Tranmission Fluid should I use

[mvmcali]

Im thinking about changing my AT fluid in my 2001 QX4 with 160k miles.
i havent done it myself yet (shop did it before)
which fluid should I use? can i use other brands besides the nissan matic D which is mentioned in the manual and is quite expensive

[VStar650CL]

Matic D is just relabeled Dexron 3. You can use anything rated for Dex 3 service.

[mvmcali]

thanks. maybe I will post this as a seperate Q but what do you think about changing more of the old A/T fluid with a method i saw on youtube. the idea is that when you drain fluid via the pan plug you dont get much out .. .but if you disconnect the hoses at the transmission cooler / radiator and drain fluid from one side while you add fluid to the other while running the engine. then in theory at least, you will replace all of the fluid. you know you are done and stop the engine when you see clear red fluid coming out. would this work?

[mvmcali]

thanks. maybe I will post this as a separate Q but what do you think about changing more of the old A/T fluid with a method i saw on youtube. the idea is that when you drain fluid via the pan plug you dont get much out .. .but if you disconnect the hoses at the transmission cooler / radiator and drain fluid from one side while you add fluid to the other while running the engine. then in theory at least, you will replace all of the fluid. you know you are done and stop the engine when you see clear red fluid coming out. would this work?

[VStar650CL]

thanks. maybe I will post this as a seperate Q but what do you think about changing more of the old A/T fluid with a method i saw on youtube. the idea is that when you drain fluid via the pan plug you dont get much out .. .but if you disconnect the hoses at the transmission cooler / radiator and drain fluid from one side while you add fluid to the other while running the engine. then in theory at least, you will replace all of the fluid. you know you are done and stop the engine when you see clear red fluid coming out. would this work?

That's actually how the best transmission "fluid exchange" flushers work, and it's also how we get as much as possible out of trannies with SMOD which aren't totally gone yet. There's nothing wrong with it as long as you keep the level up so the pump doesn't cavitate.

[mvmcali]

i think i was mistaken about how to DIY flush. since its a closed loop system, ideally i was hoping to just disconnect the outlet line of the radiator and drain from that outlet while at same time 'inject' new fluid to the inlet of the transmission (the other side of the that same outlet line) ...but i tried this before on our Miata and it didnt work. I was expecting that gravity would feed fluid into that inlet but nothing happened. I guess the pump doesnt actually create a 'pull' on the low pressure side?

youtube videos show people putting the new fluid into the filler tube while draining at the radiator...but if all that new fluid goes into the pan and if the pump then pumps from the pan to the radiator... you are kind of defeating the whole point? am i missing something? it seems this method would only work if the pump

also, on that miata , i think i ended up reconnecting the radiator hose and just drain from the drain plug but i did run the engine and shift gears to make almost all the old come out, then i refiller with new. I figured the transmission parts are already well lubed and running it dry for 1 minute wasnt going to damage anything. was this a bad idea?

[VStar650CL]

Gravity won't work. The pump is located on the input shaft and is well above the level of the pan. The technique works, but the engine needs to be running. That's why it's important to add fluid to the fill as the pump expels it out the cooler line, that way the pump doesn't cavitate.

[mvmcali]

just to be clear... where is the input to the pump , it is pulling from the pan and is that why its important to add to the fill ? ie. if the pan gets empty then the pump will cavitate?

if the pump does cavitate... am i F-ed? or will it eventually 'prime itself' once fluid is added

im looking at the FSM. At.pdf page 15 at the diagram of the Hydrollic circuit to try to get an idea of how the whole shebang works and i think i can see the output of the pump going out to all the valves and solenoids etc BUT the input to the pump isnt clear.. the diagram might be showing a tiny pic of the drain pan?

also, it shows teh oil cooler symbol but only 1 line going to it. i would have expected an input and output... maybe the tech writer was hung over when he drew that diagraM:)

[VStar650CL]

The pump sucks fluid up through the filter from the base of the pan, so yes, if the pan runs dry then it will suck air and cavitate. That's not a huge deal, it will simply make nasty noises and the transmission may run funky for a bit, but the air will usually bleed out in minutes. It just doesn't do the pump or torque converter any good to be running dry, it kind of defeats the purpose of servicing the fluid. There will definitely be two hoses on any cooler, but on the old Pathies (and probably your QX also) the cooler is in series with a heat exchanger in the radiator. So unless you've done an SMOD delete, the other hose will connect to the radiator and not the transmission.

[mvmcali]

thanks. i think im finally understanding now the full closed hydraulic circuit for the transmission. it doesnt show on the SFM diagram.
I will try to disconnect the return line to the transmission from the cooler/radiator and take the old fluid out at that point while I pour new stuff in the filler.

i was just trying to confirm that the new stuff im pouring into the filler goes thru the whole circuit before it makes its way to the radiator , anything else would mean im draining out the new stuff that i just put in the filler. kind of defeating the whole point

so to summerize how the fluid moves thru the loop,
from radiator to pan to pump to transmission components and then back to radiator?
do i finally have it right?

[VStar650CL]

A lot more of it will move into the TC and Valve Body than what goes straight into the cooler line, so you'll get most of it out. Some mixing is inevitable. I should have mentioned, make sure you pinch or cap off the return line to the transmission when doing this, otherwise it will suck a small amount of air into the return port.

[mvmcali]

thanks. good point about capping the return line, i will do that as a precaution...but im guessing it might not be critical as long as you dont let the level of fluid in the pan drop below the intake of the pump. there is probably a 'lake' of fluid in the pan with air above it all the time and not a solid volumne of fluid filling the entire housing.

in fact do you know how the fluid enters the pump ? its hard to see in the manual. maybe the bottom of the filter actually sits below the level of fluid and the fluid flows up thru the filter into the pump? im just curious how its designed, now that im looking at all this stuff.

[VStar650CL]

maybe the bottom of the filter actually sits below the level of fluid and the fluid flows up thru the filter into the pump?

Correct.

[mvmcali]

ha. i have more fun out of just figuring out how the stuff actually works than actually working on it

I dont know if you saw my earlier comment that on my 2008 miata. i actually ran the engine for maybe a minute and shifted thru all the gears when i drained the transmission via the drain plug. i was able to get out an additional 1x or 2x the fluid than had drained before running the engine .i then filled er up and everything has been fine since then (maybe a year) . my assumption was that all the moving parts were still coated with oil/fluid and I wasnt running it hot...but it sounds like you are saying that is a bad thing to do to the transmission. did I get lucky/ dodge a bullet?

[VStar650CL]

did I get lucky/ dodge a bullet?

Yep.