Tranny fluid flush for FE?
 

This past couple weeks FE hasn't quite been what I expected - off by maybe 1-2 mpg. Had been consistently 30-32 mpg before the slight dropoff.

So this past weekend I changed the oil and tranny fluid as both were due, per the odometer (3K mi. for oil, about 25K for tranny fluid).

Tanked up today and had a best-ever tank, 33.42 mpg. Granted it was all good roads and fair weather but even so, it makes me think that maybe fresh fluids are good for FE, not only good for your beast's long term health.

I flushed the tranny fluid with Penzoil non-synthetic stuff. System holds just under 8 qt. and I cycled 16 qt through it, changing 2 qts. at a time. Standard procedure for these cars however 12-14 qt does a very decent job too. Thankfully even Volvo says to leave the tranny filter/screen alone, not even look at it! Ask me again why do I love these old rwd bricks?

I've been using WalMart synthetic 10W-30 for nearly a year now. Just under $3/qt if you get the 5-qt. jugs. I can deal with that, I just can't deal with $5-6/qt. for the really good synthetics.

I dont get it. If your tranny holds 8qts, then how do you 'cycle' 16 qts through it. I must be misinterpreting something here. Can you please be more elaborate or actually more 'layman' for a regular Joe like me. I DO, however. understand that there is a FULL tranny flush that replaces ALL the tranny fluid in your system and a tranny drain-and-fill that replaces just the fluid in your pan (about 1/3 of total), but I only understand this through reading brochures at dealers that already want you to spend more money, so I dont take any of that info to full heart.

https://www.gassavers.org/gaslog/sig.php?id=547

Sorry. Sometimes I'm waaay too wordy. That time I left out too much.

Yes, you can drain the pan and you get out ~1/3 of the fluid. Of course that leaves plenty old fluid in the system.

On the rwd Volvos and probably many other cars you can do similarly to what the shops do for a full tranny fluid flush. We open the tranny fluid upper cooling line at the radiator, which on these cars is the return line to tranny. Hook up a hose going to a jug marked in quarts. Idle motor till 2 qt. in the jug, that takes maybe 2 minutes. Empty the jug. Add 2 qt. new fluid to tranny via normal fill opening at dipstick tube. Repeat multiple times till you've cycled 12-16 qt. through the system. Check fluid level when done and again next time car gets fully warmed up.

Since you only take out 2 qt. at a time you never get 100% new fluid in the system. I did a spreadsheet to calculate the %age of new fluid after each 2-qt. cycle. After 12 qt. it's in the low 90% range (I think), after 16 qt. its something like 98 or 99% new fluid.

the dealer trans flush machine can flush a bunch of fluid at a time. one dealer had a Winn flush machine, 16qts. in my place bg machine uses 10qts. its basically put in-line with the cars cooler lines, as the car runs its trans pumps the fluid to the cooler, instead of colling it goes to the machine. the machine is pressurized by the car and old fluid pushes on the bladder inside to push the new fluid into the car. their is a site glass on some machines , some times the fluid is black, after 3-5mins its a nice deep red color.
I've heard of some people leaving a cooler line off while running, using a funnel to add new fluid but some cars have high pressure that would shoot the fluid all over the floor.

Back to the topic
 

Thanks, ffvben. Good background that I'd been missing.

My reason for the orig post was to raise the question whether changing oil +/or auto tranny fluid is known to raise FE. I seemed to get a pretty good increase right after the change.

Any one else have any similar experience or related information?

All my cars always run smoother and feel a bit more powerful after and oil change, and I do typically get slightly higher tanks. I've never cycled the transmission fluid (I'm very bad to my automatics), but I would suspect that would help too.

I mean you're adding fresh, slicker fluid rather than the gunked up old stuff. Makes sense to me.

No hard results close at hand, but I have also noticed a sharp increase in FE for the first couple to tanks after an oil change.....

Shoot, I'll change the oil every other day now!

Seriously though, what I do hope to do is change maybe twoor three quarts of tranny fluid at each oil change. Calcs follow...

If I change oil at 4 k mi. intervals and change 2 qt tranny fluid at each, I'll change 16 qt. tranny fluid spread out over 8 oil changes = 32K miles. If I do 3 qts t/f every 4 k miles then I'll change 15 qt in 5 oil changes = 20k miles which is what the book specifies.

What I really like about that is that I might be able to manage the cost of synthetic tranny fluid if only changing 2-3 qt at a time. I just never could face buying 14-16 qt synthetic tranny fluid at once at the going price.

just buy 2-3 qts and put them in the back of your garage until you have a full case ;) if your changing 2 qts. at a time, the rest of the old nasty fluid will mix with the small amount of new fluid. this might be a waist of money.

Maybe. But read below.

I did some serious calcs about a year ago. Bottom line, after changing 2 qt at a time 8 times, there's 90% new fluid in there (my car). After 7 times it's 87%. Of course that's if you do it all in one session

Anyway, if you spread out those changes swapping out 2 or 3 qt with every oil change of course it works out differently but still a good thing. With the regular system, you drive on brand new fluid for a few minutes, then over the next 20K or whatever, the whole batch gets older + older till you replace it all.

This way, there's always a mix of new, sorta new, medium worn, etc. etc. fluid in there. Should be good, I think. Maybe every 30 K miles or so I'll do a full flush. Something like that. Shucks, plenty people drive 100-150K with no maintenance and then the say "gee, the tranny is slipping, they just don't make 'em like they used to".