Trans flush vs drain and fill

"Future next gen S2000 owner" (future-next-gen-s2000-owner) 10/15/2018 at 11:00 • Filed to: DIY

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In the never ending saga of wanting more than my budget allow, the Saab needs some preventative maintenance to extend its life until the budget allows for a CTS . It is time for a trans service. I’ve only found !!!error: Indecipherable SUB-paragraph formatting!!! online about !!!error: Indecipherable SUB-paragraph formatting!!! . My mileage puts me at the interval for a flush.
Is it possible to flush the transmission in your driveway?

A drain and fill takes about 4 qts while a flush takes just shy of 8 qts . Should I just do a couple drain and fills? That should get most of the fluid swapped. Right?

For your time.

Gerry197 > Future next gen S2000 owner 10/15/2018 at 11:12

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For an auto, there is some worry that if you do a flush, especially for an older transmission with some miles on it, that it loosens debris in the transmission which “messes up” the transmission.

I my E46 forum, it seems to be a 50/50 shot that it will actually screw up the tranny. Could be coincidence of course and simply just a myth in the community, or it could be based on reality.

But the pan drop, change filter and refill seems to be a sure way to do a fluid change without risking damage on a old automatic. It doesn’t get to all the fluid, but it’s a chance to change a lot of it without flushing the system. You can do it a couple of times in close succession get most of the fluid out of the system, which is still better than your situation now.

For me, I recommend going that route just in case.

Quadradeuce > Future next gen S2000 owner 10/15/2018 at 11:14

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I only ever drop the pan, swap filters, then refill.  I’ve never flushed anything.  And I’ve never had a trans fail me.

Future next gen S2000 owner > Gerry197 10/15/2018 at 11:14

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I’ve heard about that fear. Essentially you clog a port, which causes the damage . The fluid was swapped at 90K miles and has a 60K interval. So I’m at the manufacturer interval.

It is an auto. I’ll have to see if I can find info on dropping the pan.

Gerry197 > Future next gen S2000 owner 10/15/2018 at 11:19

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Cool, so you have a flush at interval, then I probably wouldn’t worry.  I do have some old cars, 98' Grand Cherokee & 93' Ranger that have autos, my very good Indy mechanic who has a high end flushing system has actually told me not to flush those trannys, but do pan drops only.  However, my old vehicles have not been on a regular tranny service.   

Party-vi > Gerry197 10/15/2018 at 11:21

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This is a myth AFAIC. BMW shops won’t do it because they don’t want to be responsible for any transmission issues that might crop up, because any BMW that needs an auto trans service is going to be at/over 100,000 miles. I had the trans fluid flushed twice on my E46 (made it over 200,000 miles) and never had a problem.

BrianGriffin thinks “reliable” is just a state of mind > Future next gen S2000 owner 10/15/2018 at 11:35

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I’m in the drain and fill camp, too. I wouldn’t even drop the pan if it has a drain port. 

Gerry197 > Party-vi 10/15/2018 at 11:39

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I would generally agree with you on that, though I got two old cars without warranties that would both be considered “totaled ” if I had to do any major tranny work on either. If rather drop pan on those.  

Future next gen S2000 owner > BrianGriffin thinks “reliable” is just a state of mind 10/15/2018 at 11:42

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From what I’ve been finding online, a “flush” is simply repeating a drain and fill 3 times. Which in theory leads to 87.5% new fluid.

I’ll be checking the manual over lunch.

deekster_caddy > Future next gen S2000 owner 10/15/2018 at 11:49

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I’ll second this train of thought - just do a pan drop and filter change, don’t do a flush.

deekster_caddy > Party-vi 10/15/2018 at 11:51

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It’s not a myth though. It’s circumstantial, but it’s a strong relationship. Flushing transmission fluid has caused problems for many people I know.

Bylan - Hoarder of LS400's > Future next gen S2000 owner 10/15/2018 at 12:06

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Ive heard the flush myths too much, at 190k I did a pan drop, filter change, and 2 drain and fills on my LS400. About 2-3 quarts of the total 8 fall into the pan, so I’ve replaced most of the fluid now with Toyota T-IV fluid. 211k now and the transmission was noticeably snappier ad soother after the cleanup. I don't see the upside of a full on flush. There’s my 2 cents

Long_Voyager, Now With More Caravanny Goodness > Quadradeuce 10/15/2018 at 12:31

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The only high mileage trans that ever failed on me (not from obvious abuse) was the one I had a flush done on. 5k later I lost 2nd gear and reverse........

Quadradeuce > Long_Voyager, Now With More Caravanny Goodness 10/15/2018 at 13:04

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A story as old as time...

BrianGriffin thinks “reliable” is just a state of mind > Future next gen S2000 owner 10/15/2018 at 13:18

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That’s not what most folks (and shops) mean when they say flush. Yes, doing a repeated drain and fill is a good idea. You can either do it all at once (drain, fill, drive for like 25 miles, repeat x 3) or I just like to do it once every 25-30k miles.

When you talk about “flush” with a shop, it’s when the trans is hooked up to a pressurized machine to pull/push all of the fluid out, including from the TC. This is what’s scary and can lead to metal parts going where they shouldn’t. 

Long_Voyager, Now With More Caravanny Goodness > Quadradeuce 10/15/2018 at 16:04

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I honestly never believed it until it happened to me....