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If it hasn't been changed yet, don't change it now - fact or fiction?

I have read and heard from people that if the transmission fluid has not been changed and your car has over XXX,XXX miles, then it can do more harm than good to change the fluid now.

I’m not asking about my current car, but about a car which I am looking at with 158,000 miles about which I do not know whether or not the fluid has ever been changed.

Is this correct or not?

It is best to follow the manufacturers instructions on maintenance which includes fluid changes. If a fluid change is over due it should be done. A urban legend is a transmission should not have it’s fluid changed if the fluid is very old. This is probably due to an old transmission having trouble, the fluid was changed and then a failure. The failure being blamed on the fluid change when the failure was going to happen any way. Check with your friends etc to find a good local independent tranny shop to look this car over. The best service assuming no other problems is to drop the pan, clean/replace the filter and replace the fluid. Replace the pan with a new gasket.

I’d advise against any transmission “flushes” especially those performed by quick oil change facilities.

I would advise to drop the pan, change the filter (if it has one), clean the pick up screen, and refill with the correct fluid.

Correct fluid is very important and many facilities use a “universal” fluid and that stuff can harm some transmissions. If this transmission is a CVT type the correct fluid it critical.

If in doubt use the fluid with the mfg’rs brand name on it. Honda’s are very fluid sensitive so if it happens to be a Honda you are looking at I’d get Honda brand fluid for the refill.

If in doubt, change it out. Fresh fluid will not cause a failure and a pan drop is the safest way to change it out. I would take a white cloth and use it to wipe the dipstick and really scrutinize the condition of the fluid. It should be nice and pink with a healthy smell. A burnt smell and orangy fluid would have me thinking twice or offering a lower price. Ditto if there is a lot of dark particles on the cloth.

If the tranny fluid is dirty, black, or smells burned you should avoid the car.

If the transmission has already been damaged by neglect, new fluid won’t help.

Personally, I would avoid any used car if its maintenance was an unknown, and I think that a 150k+ mile car with an unknown history of trans fluid service has a giant red flag waving over it.

As to what the OP has heard from people regarding some kind of danger resulting from changing old trans fluid, consider this–Some old people will tell you that placing a knife under your bed, “Cuts 'de pain in half”. Would you believe that statement?

Yes, there are people who actually believe silly “wisdom” like this, and there are apparently even more people who believe that it is advisable to keep using ancient trans fluid. Kudos to the OP for trying to verify the bizarre–but commonplace–advice that he was given.

When my late Father-in-Law gave me his 1993 Caprice (with 44k miles) in 2002 the transmission fluid had never been changed. My trusted (+20 years) mechanic was concerned about doing a transmission pan drop and filter change. He explained that varnish can build up on the trans interior surfaces over time and the introduction of fresh fluid could cause the flakes of varnish to break off and clog the interior passages of the transmission. He wanted to give me fair warning and not to blame him if there were any issues after the fluid/filter change.

Since the fluid was still clean and bright red I had the work done and there were no problems.

Ed B.

@jesmed‌ Assuming that there is nothing obviously wrong with the car when I look at it myself, I am going to have it checked out thoroughly by a mechanic prior to purchase, including checking the condition of the fluids, and I will pass on it if they tell me that the transmission fluid is dirty, black, or smells burned.

@VDCdriver‌ I would also avoid a used car if maintenance was unknown, provided I had the funds to be choosy enough that I could eliminate the sellers who do not have all of the maintenance records.