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changing transmission oil bad?

bohdanbohdan Member Posts: 1
edited March 2014 in Mazda
I have a 109K Mazda 626, just bought, and want to
change the transmission oil. I read in a book that
this can make things worse, create new leaks. That
it's better to wait until the transmission is ready
for an overhaul before changing the oil. I'd
appreciate any advice on this.
Bo in Miami


  • bill11770bill11770 Member Posts: 29
    i heard that too.... but i'm not sure of it. i believe the theory is that the new fluid would loosen up gunk that's been built up over the years, thus leading to a plug up somewhere.
  • rs_pettyrs_petty Member Posts: 423
    go to and read about the TTS.
  • poisondartfrogpoisondartfrog Member Posts: 102
    To lessen the change of dislodging gunk, I'd opt for a flush of the tranny. It's a little more expensive than a filter/fluid replacement, which maybe removes 70% of the fluid capacity at best, but the flushing also removes the fluid from the torque converter, too.

    Age, contamination, and heat cycles are what damage seals. New fluid into a flushed tranny is your best bet for continuing the life of that tranny.
  • sable93sable93 Member Posts: 107
    I don't know if you are still deciding whether to do this or not, but I recently had the tranny fluid flushed in my car ('93 Mercury Sable.) No problems, and it even shifts a little better than before.
  • rea98drea98d Member Posts: 982
    What I heard is that if it leaks after you flushed it, you had leaks anyway, but they were plugged up by all the gunk you flushed out. My grandma had a similar thing happen on her 1986 5th Avenue. Bought used, probably around 92 or 93, and the PO never changed engine oil. Once my grandpa started doing regular maintainence, all the gunk came down out of the engine, and clogged everything up. It got where it wouldn't go one mile without dying several times. Had a mechanic disassemble the engine and flush everything out, then he said he wouldn't gaurantee it to get to the end of the driveway before it died. She sold it for a 92 Bonneville.
  • butch11butch11 Member Posts: 153
    Read an ad for a tranny flushing system in a mechanics magazine. Said it flushes the tranny with a solvent which removes gunk and helps preserve the seals. If they use a solvent to flush out the tranny, some will remain in the tranny and it may do damage to the tranny. If you plan to pay for a tranny flush-find out what they are using to flush with-you maybe killing your tranny because the new trannies are really particular about having the correct atf used in them.
  • rdeschenerdeschene Member Posts: 331
    I have had the atf fluid and filter replaced on my Corsica a couple of times; my previous car (87 Taurus) died as a result of a fried transmission so I'm a bit paranoid.

    At any rate, it is often said that transmission failure is the result of overheating, however, the ROOT CAUSE is typically fluid loss through a cracked hose or rusted-out line (my Taurus!) or a leaking gasket. So if replacing atf shows where the leaks are, that's actually a good thing because then you can see which hoses, gaskets, etc. need to be replaced. My 2 cents. R.D.
  • 0patience0patience Member Posts: 1,712
    It specifically states that the transmission fluid should be changed at regular intervals,usually around 30,000 miles. Having your transmission flushed without dropping the pan and replacing the filter is useless,all of the debris will be pushed into the pan where it will be picked back up again.If you have a flush done on your trans,then afterward drop the pan and replace the filter and clean the crud out of the pan.If it is done right it is very beneficial to the life of the trans,but it can also be done wrong and create more headaches.As for the leaks that the books talk about,they are refering to the pan gasket,which is a joke,it may or may not leak,it depends on how diligent you are to clean the pan and gasket.Again,owner's manual will have a specific interval for trans servicing,FOLLOW IT!!
  • mosaicmosaic Member Posts: 2
    My '94 Grand Am recently turned over 100,000 miles. Regrettably, I'm guilty of never servicing the transmission. Spoke to a mechanic w/25 yrs exp. - said similar to previous: if you change it now, it will strip the glaze off the gears and you may end up needing a new trans. before long.
    Dilemmas, dilemmas !
  • poisondartfrogpoisondartfrog Member Posts: 102
    I find that hard to believe... since it's 6 years old, and from the mileage i would assume from highway driving? If so, those are easy miles for a transmission... less temperature cycling on the fluid than if you were stop-and-go for 100K miles. How does the fluid look? If it's still reddish pink, I'd move forward with a change. In fact, if you're that worried, change it now and change it again in 15K miles. I wouldn't flush it, but just a standard drain/fill fluid and filter change.

    My experience with pan gasket (leaks)... I typically use Fel-Pro gaskets (not cork); usually I have to re-torque (criss-cross pattern) the pan gasket bolts after a few heat cycles. Otherwise, I develop a small leak, since the gasket takes a heat set. Once I re-torque them, no leaks until i change it again (30K mileage intervals).
  • billybreathesbillybreathes Member Posts: 14
    I had a 1989 Honda Prelude with 161k, never changed the trans fluid (automatic). Bought the car new, and the book has no interval as to when to change fluid (or timing belt, which led to the demise of this great car).

    So I never knew I had to change it until the car had 100k. At 100k, I brought it in for service, and my mechanic/friend told me "if it's never been changed until now, don't change it". So I didn't and the car's tranny was fine right until the original timing belt broke at 161k.

    My friend had a Mitsubishi Starion with 96k, he changed the tranny fluid even though the tranny was fine, and the tranny was roasted at 98k. My advice- if it ain't broke, don't fix it (except with timing belts)....
  • johndopejohndope Member Posts: 7
    Precision tune recommended my girlfriend flush her chevy celebrity's trans. The car has 52,000 miles on it and I assume that the trans has not been flushed in its lifetime. Should she follow the mech's advice and flush it?
  • joe3891joe3891 Member Posts: 759
    Heat is the enemy of trans. fluid,the newer fluid is better.In years past if you left fluid in to long it would jell an then an overhaul.I dont flush,i do what i have done for years drop the pan an clean it,replace filter& fluid,do this every 30K.Costs $15.for a filter an $5.for fluid.$20.every 30K is cheap maintance.Heavy duty Allison trans.recently call for a 15K fluid change,drop pan an change fluid an filter they dont flush either.I dont see anything wrong with flushing i just dont like wasting money.The 4qts is more than enough to revitalize the fluid,an changing the filter is very important i seen old filters come apart an what a mess that makes.I thought i would give my opinion from experience.
  • alcanalcan Member Posts: 2,550
    Right on target, Joe. The fluid itself will stand up, but the additive packages (corrosion inhibiters, friction modifiers, oxidation inhibitors, anti-foam agents, etc, etc,) DO break down, especially under severe service. This includes, btw, police, taxi, city delivery, towing, sustained high speed operation in high ambient temp., driving in wet snow, repeated hard acceleration, and over 2K/month of city driving. All these conditions tend to raise fluid temp. and deteriorate the additives. I've been rebuilding and servicing automatics since 1969, and my recommendation has always been to change the fluid and filter every 3 years/60K kilometers (about 36K miles) for normal service, shorter span for severe service.
    The myth about changing fluid on a high miler and then having a catastrophic failure is exactly that, a myth. Usually traceable to pure coincidence (Murphy is a mechanic) or the fact that the trans was on it's last legs anyway and the owner was trying to Band-Aid it.
  • sikousissikousis Member Posts: 2
    I recently bought a 2000 1500 Ram Dodge Cargo Van which I use in NYC. At 5,000 miles I took it back to the dealer and asked him to change the tranny oil, filter and clean the pan. My thoughts are that at breaking in there are small metal particles building up in the oil and in the filer. I plan to change the tranny oil and filter every year. Inaddition when I order the van I had Dodge install a factory tranny oil cooler which I understand helps in my type of "STOP AND GO TRAFFIC"
  • alcanalcan Member Posts: 2,550
    Smart move. You'd be amazed at how much casting sand and other assorted trash I've found in the pans of virtually new units. And the cooler, along annual servicing, will go a long way toward keeping your tranny happy for the severe service it's gonna see. :)
  • don434don434 Member Posts: 43
    Had transmission rebuilt at 97,000 miles due to slippage at Glen Burnie Transmission in Glen Burnie Md.
    On day I picked up the truck I drove three miles and stopped for a meal. After eating I checked the fluid level it was about two inchs above the cross hatch area. Returning to the shop right away I asked the service tech to verify level. He said it`s a little high but O.K.
    Three weeks later I was heading out on a long trip so I stopped by the shop for a level check. The service advisor said it`s about a half pint low.
    He found a funnel about 3 feet long which ended up jammed against my under hood mat. He held the funnel with one hand and picked up a 2 gallon plastic container of fluid and glug glug into the funnel. As he sat down the plastic container the funnel fell spilling fluid across my battery and A.C. hoses. Again he picked up the funnel and can and glug glug - more fluid into the funnel. He again checked the level and said your good to go.
    About three days after my long trip I noticed pink fluid on my driveway. I checked the fluid level and it was about 4 inchs above the top of the cross hatch hot fill area. It was checked on level ground - in park and with a hot engine.

    Question is can an overfill cause my rear seal to leak. It now drips after every trip. I see red fluid on the first drive shaft section past the transmission. The service guy at Glen Burnie Transmission said it`s just draining out a pressure relief valve and this is O.K. Paid them $1,700 for this work.
    Any Comments?
  • alcanalcan Member Posts: 2,550
    When a trans is way over-filled, the fluid level is high enough that the rotating components are semi-submerged. This causes fluid aeration which builds pressure in the sump. Your trans has an atmospheric vent through which aerated fluid was probably being blown out. If pressure was high enough, it may have damaged the rear seal. Also, check for play at the front slip yoke. A common cause of rear seal failure is a worn trans rear bushing/slip yoke outer diameter.
  • don434don434 Member Posts: 43
    Thanks much for your input. My last question is:
    Should the transmission rebuild shop have checked the rear seal and rear bushing/slip yoke when doing a $1700 rebuild job or is this something I should not expect them to do?
  • alcanalcan Member Posts: 2,550
    The rear seal is usually replaced during an overhaul, yet almost all seal/gasket kits don't include one. Go figure, huh? As for the rear bushing, it should have been replaced if there was excessive play in the slip yoke or any evidence of slip yoke wear.
  • armtdmarmtdm Member Posts: 2,057
    Previous posts state that the fluid was checked when engine hot, however, no mention of whether the engine was running. The engine must be running and the fluid hot to get a proper check. It will always read overfill if the engine is not running!
  • don434don434 Member Posts: 43
    the engine was running. Honestly the day of the double try to add a half pint from a two or three gallon plastic bottle the level was just past the Z bend on the dip stick.Level ground engive running and hot and in Park. Roughly about 4 inches of overfill.
  • dweezildweezil Member Posts: 271
    Now I KNOW this claim is only for salesmen who cover 24,000 miles of easy Highway driving or for people who WANT to believe it's true.Personally I think it's foolish. I have 15,000 miles on my Cavalier w/4 speed auto. I live in L.A.60%street 40%freeway. Gave it it's 1st oil change @ 1300 miles, then again at 3000, and every 3 months regardless of mileage. I don't buy the owner's manual claim that "severe duty" you can go 50,000 miles. I plan for this to be a lifetime vehicle as car payments irritate me.I am thinking of going to the local Jiffy Lube and having them do the Ultra Flush where they eliminate "95% of the old fluid" by flushing fresh fluid through the trans.I have heard that this trans. is "sealed".I don't want to get to 40,000 miles and lose a trans even though I have followed the "recommended" service schedule. I did the early break-in oil change because any machine has to wear down metal to run correctly and to have everything mesh properly, and by doing so I have extended the life of my engine. Any suggestions/recommendations? I think I should trust my instincts but don't want to void my warranty. THX, Dave
  • wtdwtd Member Posts: 96
    I first changed the tranny fluid and filter on my 98 chevy ext-cab Z-71 at about 20,000 miles. At the same time I replaced the tranny pan with a factory replacement that had a drain plug. I read somewhere where a guys dad would change his tranny fluid at every oil change(his pan had a drainplug)and change filter every 30,000 miles and ran his vehicle over 200,000 miles with no tranny problems. I'm thinking of doing the same thing on my truck if I decide not to use synthetic tranny fluid. An extra $5.00 at an oil change isn't much and you would always have fairly new oil in it. Most of my driving is stop and go in the city which is the hardest on trannies. Is this just a big waste of fliud or would this practice potentially increase tranny life?
  • dweezildweezil Member Posts: 271
    Sorry for my lack of clarity. I'll keep changing the oil every 3 months and the fluid at every 15,000.Alcann, Thanks for the post #'s, I'll check them. These transaxles are NOT cheap to replace and I know it's a lowly Cavalier,but I don't want to go off blindly and have a schedule for my type of driving that will cause it to burn out at 50,000 miles.I appreciate the tips. I have had old cars for so long by the time they get to me preventive maintenance is something the car hasn't seen since the first 3 years of payments.
    These extended service intervals are really misleading and I don't trust them;just don't want to be so plugged up about it that I cause harm to my vehicle.Wtd;I think changing trans fluid as often as your motor oil is probably too often even for my neurotic tendencies!Ha,thanks for the advice, both of you. Dave
This discussion has been closed.