Any truth to the "myth" about changing transmission fluid in older vehicles?

Question

I have had people give me anecdotal stories (friend of a friend type thing) about changing the transmission fluid in vehicles with 150,000+ miles, especially those that haven't had regular transmission maintenance. The usual story is something along the lines of "older American make care with 200,000 miles, a week after we changed the fluid, the transmission went out."

Is there any truth to this? Best answers I could find searching the internet were pretty inconclusive at best, such as yahoo answers with unhelpful answers like "if it ain't broke, don't fix it."

With my vehicle in particular (2000 Chevrolet Venture), I had a transmission repair and fluid change at 130,000 miles, and am now at 190,000 miles (so it is a little overdue for transmission maintenance). I've had a little hesitation in shifting: I talked to my mechanic and he likely said it's a sticky solenoid, and he suggested a cleaning transmission treatment (such as Seafoam), but he hasn't looked at it. If I understand correctly, such treatments are usually best followed by a fluid change.

If I have to do a major repair at this point, I'd pretty much declare the vehicle "junk" instead. So I'm fine with doing some minor maintenance to keep it going for a couple more years, but don't want to do anything that will possibly harm the transmission or make the problem worse.

Answer 1

NOTE: I have anecdotal vs. empirical data on this, so please understand that caveat.

I believe the problem which is actually being discussed is doing a transmission flush when it has never been done before (or with long periods without). The theory is, over time, buildup occurs within the transmission when flushes do not occur at regular maintenance intervals. If you remove this buildup, you leave gaps in the soft parts (clutch material) which means less material for the transmission to work with. This causes faster wear in the material which is left, which causes the transmission to need rebuilt sooner.

If the transmission has had regular flushes, this buildup does not occur as well as wear/tear not occurring due to buildup.

Please note, changing just the fluid (dropping the tranny pan method) under the same conditions (long period than specified between fluid change) would not have this same effect. This is because the buildup solids would still be in place. The reason a flush could be more detrimental is because (to my understanding) the way a flush works is by forcing fluid through the system backwards, freeing up any solids which may be in the filter or elsewhere and forcing them back out through the system. This not only cleans the filter, but also replaces all fluid in the transmission. When you drain by dropping the pan alone, you are only changing out the fluid which resides in the pan. There is still a large quantity which remains in the torque converter.

To this end, I've seen transmission which get flushed, having never had the fluid changed, destroy itself within a few thousand miles. Yet, the same type of vehicle, if left alone, would have lasted many, many more miles without the flush. Mind you, as stated, this is subjective. Bottom line here is that rule of thumb dictates, if you haven't kept up on your transmission maintenance, don't do a tranny flush. It will more than likely destroy your transmission. Getting scheduled maintenance on an automatic transmission is by far your best recourse.

Answer 2

There is a lot of debate about late ATF changes killing transmissions. To find the real answer you would need a statistically significant number of vehicles for each transmission, and a same-sized control group, driven identically for hundreds of thousands of miles... then one group serviced, the other not, then all driven identically for another hundred thousand miles... that's not going to happen.

The best I can offer you is some advice.

For older transmissions with deferred (heh) or without any scheduled maintenance, I take the Honda approach. Remove, measure and replace a small amount, about a quart/liter. Drive for several thousand miles and monitor performance and behavior. Then replace a larger amount, maybe 2 quarts/liters. Repeat driving and monitoring.

If a filter exists, replace it only after several cycles.

The approach I started on my then not-so-old vehicles is simply replace 2 to 3 quarts of ATF every oil change. Now, they are getting old, as in 150K miles each, and both have perfect transmissions. I just keep doing the same thing, also replacing transmission filters occasionally.

Transmission wear can be tracked primary through vendor-specific electronics and ODB2 codes, but in OBD2 anything in the Transmission section with the terms Range/Performance can be useful.

Answer 3

I am not a mechanic but have owned many cars and a high millage driver. I had a 2004 chevy malibu it was running perfect. I had the oil changed every 6,000 miles (as per the manual said) and I was at 160,000 miles it was suggested (by the shop) to get a transmission flush (this is not in the owners manual). I agreed and I got it done (the transmission started to slip immediately) and 200 miles later ( which was only 2 days) my transmission went out. I was out all the money to have it done, and now had no car. I know my car had no problems or anything before and definitely no transmission problems. I do not recommend having this done to any car that has never had any type of transmission service before. All of my prior cars, 1989 chevy corsica had 287,000 miles on it before i traded it. Had a honda del sol, had 190,000 when i traded it for a brand new 2000 chevy cavalier had 230,000 miles before i wrecked it. Then bought another 2000 chevy cavalier and it had 270,000 when I traded it for the malibu. Not one of my cars except the malibu had a transmission flush. All of the cars worked great. the cavaliers both had a fuel filter issues but that was it and that was around 170,000 on both of them. The flush is a ploy to make more money, its a scam. Mechanics say it will make the transmission last longer, I want proof. You want proof that the flush ruins the transmission, I think we can prove that. But can you prove it makes them run longer? Currently I drive a 2011 Hyundai Elantra bought brand new. Has 171,890 miles on it and guess what, I have never had the transmission flushed. The car runs fine. (not the best car but it runs fine) The average life of a car is about 200,000 miles according to google. So why get the transmission flushed if it won't extend the life anyway?

Answer 4

I have never heard of such a thing before and it also doesn't make any logical sense. On the contrary, if you e.g. change your engine oil every 3000 miles instead of the "recommended" 10000, your engine will last practically forever. A friend of mine has a Honda Civic with 800 000 miles on the odometer and he changes his oil every 6 weeks (he does about 3000 miles in that time). Granted, Hondas are pretty reliable, but 800k miles is a bit of a stretch even for a Civic.

Seeing as a transmission is also a large piece of moving metal parts, I can't see how it would react in an opposite way to frequent oil changes. The most important thing though is putting in the CORRECT oil.

UPDATE: Now that I know a bit more about oils, it turns out that fully synthetich oil will "leak" more easily that dino oil and therefore if your transmission had a pre-existing problem, synthetic oil would make it more apparent. It's not the oil though and it won't make the transmission break.

Answer 5

The debate about transmission fluid change revolves around a basic problem. Typically, a transmission pan drop & fluid change only changes about half the fluid. The fresh fluid effectively cleans the transmission and releases particles of old build-up, which circulates throughout the transmission, leading to slipping gears, pressure drops, overheating, even complete failure.

The solution is to change the fluid three times in relatively short order, such as several days between changes after some highway driving (or immediately if you notice adverse performance after a fluid change). In this manner, the transmission will be thoroughly cleaned without damage. You can further remove dislodged particles by using a detergent for 15 minutes at idle before each fluid change (I've used Amsoil Engine and Transmission Flush). You can save money by pumping the fluid out through the dipstick after the first time a mechanic changes the filter.

I have personally resolved minor transmission problems -- such as hard shifting and poor gas mileage -- with a fluid change. It can only improve the condition of the transmission.

Answer 6

It is very true, do not do it!

Backstory

I'm an A.S.E. Master Auto Tech, and have been for 28 years. A very popular chemical company was in my shop "training" my technicians (not lube techs) on how to use their equipment.

I allowed them to use my GMC Yukon as the training vehicle, they flushed it on Wednesday, and I lost 3rd and 4th on Saturday. I had no prior problems with the transmission in the vehicle, NONE, it shifted like a champ.

I have a ex-trans builder working for me, he explained that new fluid will completely destroy old clutches in the transmission. When we pulled my 4L60E apart that is exactly what was wrong - the detergents in the new fluid just destroyed them.

If your transmission has not been flushed at 120K miles do not do it. This is very true!

Answer 7

I've purchased two vehicles with poor transmission maintenance from previous owners. First car was probably already suspect of failing. Having changed the AT fluid using the gentler drain and fill method I had to replace my transmission within the month. It started slipping more often. Before the change it didn't slip at all.

My second car I did the drain and fill too, than it jerked harder on shifting third to fourth. Bad news is I had to rebuild the transmission a few weeks in too.

In both these cases however I think the real news was the transmission was going out, changing the fluid was a shot at remedying the solution for the cheap. The real solution was probably just to save the $50 in fluid and do the transmission right off the bat. I'd say if you suspect the transmission is starting to wear maybe just drive it til it breaks because the fluid may speed things up either way it doesn't harm what's already broken. I really wish I could of just driven it til the transmission blew but having babies in the car I could not do the waiting for a tow truck thing.

Both my cars were SUVs and 135k miles and bought from a second party.

I don't have a real solution for you because every car is different but this was my first hand experience with the transmission.

Also never let the dealer perform a flush it's a violent way for fluid to get pressured through the system and you end up clogging the small capillaries inside the transmission leading to failure. Drain and fill is a gentler way to do it, fluid drains out slowly than you fill it back up. But this won't get all the fluid out in one go. I'm going to do my drain and fill every 15k miles from now on to maintain the rebuilt transmission.

Answer 8

Having previously worked in automotive oil industry I can definitely say NONE of the car makers make their own oil. Afton Chemical and Lubrizol are the two primary factory fill oil companies.

The ATF today are engineered and road tested for ~150k, the exact upper limit is debatable due to environmental factors. So you do need to change the ATF if you keep the car over that mileage. Changing it under 100k in normal driving maybe overkill.

Also you can't judge the condition of the oil just by the dark color.

And car manufacturers want to scare consumers to death about using aftermarket oil. It has to do with branding and specific additives in the oil. However, those secret additives are not so exclusive to MB, Honda or whatever you drive. Mobile, Valvoline Quakerstate etc also can put those additives into off the shelf compatible oil but they Usually don't mark the latest oil compatible due to exclusive licensing and liability issues.

Answer 9

Hi I'll add my experience to the treasure trove above. All of which I have heard and experienced on a few cars.
My theory is that completely changing the ATF on a non-maintained tranny with over 100K on it loosens the built up deposits on the clutch seals which get hard, shrink, and develop mini cracks over time. The deposits keep the mini cracks and looseness sealed (much like the radiator sealer chemicals you might use in the cooling system) until they get washed out with the detergents in the new ATF. The complete replacement of the ATF in such a tranny will clean the deposits out of the cracks and loose fitting seals very quickly causing no clutch action and no more driving. My theory is to change the ATF slowly enough that it the ATF softens the seals faster than the detergents wash them out. I have replaced the ATF in a couple of unmaintained cars successfully using the slow replacement method. Start by changing out the filter and about 10 % of the fluid . If you end up draining more than 10% of the fluid, simply catch it in a clean-as-possible drain pan. Then pour the drain fluid into a clean jug through a filter material like cheesecloth to catch the big chunks.
Pour your 10% of new fluid into the tranny first, then fill it up with the drained fluid. Now drive it for 6 months or so and do it again, but this time change out 25% of the fluid and you don't probably don't have to change out the filter unless you can see a lot of deposits. Then do it again in another 6-12 months but change out 50 % of the fluid. What this does is allows the new ATF to soften up and swell the seals enough that they will still seal even when the deposits are removed. (At least that's my theory) and it's worked on three cars with 160K to 200 K miles on the trannys. Again, just theory and practical evidence that this has never caused a tranny failure for me even with 50K to 100K miles on each tranny after the first 10% change.

Good Luck!

Answer 10

If you have not had your transmission fluid changed per the recommended schedule in the owner's manual, and you don't know the vehicle's history, I would not change it unless you are prepared to repair/replace the tranny. I just purchased a car with over 150k miles on it and at the recommendation of the Honda Dealership, I had the transmission fluid changed. I had no problems with transmission prior to the service recommendation. Anyways, following the fluid change, my transmission failed days later. This is not a myth, it's a fact.

Answer 11

One factor that has not been mentioned ; the make of car.However my reference point are old. I changed oil in several American cars, mostly Old and Buick turbo 400's from the 70's and 80's. Often I needed a putty knife to get up to a quarter inch of sludge off the bottom; It is easy imagine some of this material fouling valve bodies, etc, causing trouble. When I changed oil in an '85 Nissan 300ZX , the pan was clean ( 75,000 miles) , one paper towel cleaned it to a shine ( it was painted ). So no possible dirt re-circulation problem. So I say older American cars are a problem area.