Any fluid change - the reason why?

I'm excellent about changing my oil - I get it, oil gets dirty and loses some viscosity (thickness) causing it to not lubricate as well. I am changing my transaxle AFT soon, yes I will use the Toyota WS ATF - but I am changing it because many think it's the right thing to do (and I can draw a parallel to changing the oil) - but if the original thickness of a fluid changes over time, and the lubricating qualities become in question (over time), why would there be so much discussion about "when, and IF, I should change the fluids". Sure, it can be a function of how you drive, and the stress you put on the motor, gears, brakes, … but this can be estimated within bounds and guidelines given (like the oil change) for changing the other fluids. I know many that never change the brake fluid – I know many that never change the transmission oil, that never flush a radiator, and there are some in this forum that agree with this. Does someone KNOW if we should change the fluids due to a lack of lubrication quality and viscosity change?

I personally know of a person who did not change their brake fluid and after 120K miles or so, one day the car did not stop and he ran into someone - thankfully it was a minor accident. The service shop told him the brake fluid was like water and it had never been changed. As it's a closed system, I'd think even 'water' would push on the brakes and activate them, but the 'holding power' may not be there.

So, is the reason we change fluids in cars is because the fluid viscosity changes over time?

If this is true, there should be no discussion about changing fluids – it should just be done – at some interval – and it’s up to us to determine what interval that is, how hard we drive the car, how many miles before any fluid change is necessary. We have owner’s manuals that give us guidelines in these areas.

Thanks for your thoughts.

 

Good points. There are 2 scenarios here, 1) we read about the unsuspecting person going to the dealer and getting 'taken' for much more than is necessary. My sister is typically this person.. "you should have this done, that done", she does not know, so she does what’s recommended.. costing her $500+ each time. The last time at the Dealer, recently, they got her for a new 12V battery (19K miles on the car; $300!!! ) and told her she needed new tires (which thankfully she did not buy into - and she'd checking with the manufacturer. The 2nd scenario is that you have some idea of what you are doing and you either do it yourself, or at least take it to a 3rd party shop that does it for much less than the dealer. In both cases, it's not known if the fluids should be changed, but it's perhaps its done due to mileage, or general concern, or as you say, buying insurance. The problem I have with this is that there are many cars running today that have not had a tranny flush/ fluid change, brake fluid change, radiator flush.. and the cars are doing great. I'd bet more like this than not. If you believe that (and you don't have to) - are the fluid changes really necessary? Is the WS ATF really good for the live of the car, and only to be inspected at 100K+ miles as the manual states? Heck, I don't know. Just trying to figure this stuff out. (Oh, I am planning to change my Prius ATF soon - but I really question if I need this done - as the manual indicates "no".. or I have been convinced by forums like this one, that I should do it)

 

Great input. Thanks. I appreciate the discussion on brake fluids.