rev up your engines today I'm gonna tell you why you should flush the toilet in
your house but not flush the transmission in your car now for the last 52
years people are asking me Scotty somebody's trying to tell me I
need to flush my automatic transmission have it all flushed out and new fluid
put in is that a good idea and I generally say no it's not a good idea
now the reasoning behind flushing isn't a bad idea
realize most automatic transmissions when you drain the pan take it off empty
it out maybe three four quarts of fluid comes out and some of these systems hold
like 14 15 quarts so a bunch of the old fluid remains inside especially inside
the torque converter because it's not like flushing your radiator system out
which is much simpler now radiators have tiny halls that the coolant has to go
through you want to keep it clean so that all those passageways don't get
clogged up and the cooling system is very simple you got a radiator and flows
through you have a water pump that pumps it through the system goes through the
jackets of the engine inside to take the heat from the engine and then pump and
dissipate it through the radiator simple system you don't want to clogged up a
mechanical or in some cases the new ones are electric pumps they still just pump
the fluid so you flushed it out you get all the crud out you're not gonna have
any problems but automatic transmissions completely different animal here
automatic transmissions are very complex inside they have electric solenoids they
have tiny little passageways that go by pressure differential you have dirt in
your automatic transmission and you run a power flush that's power pushing the
fluid through the system those tiny little holes some of the crud could be
pushed into the little holes jamming them up I have seen hundreds of people
have the transmission flush somewhere else they bring it to me and say Scotty
my transmission is slipping now or it won't go into gear or shifting rough and
it wasn't doing it before I had the transmission flushed and it's true that
can easily happen the best thing to do is to drop the transmission pan clean it
all out and check the filter the filter is there to catch
most of the crud so you dropped the pan clean the dirt out in the bottom put a
new filter in then the system is good to go if you do it regularly no when I was
a young mechanic in the nineteen sixties we would change the transmission fluid
and filter every thirty thousand miles the fluid wasn't as good the
transmissions weren't as good and it had to be done more often now today the
transmissions are better the fluid is better I would still change it every
sixty thousand miles or so in any vehicle and for heaven's sake don't
listen to those people that say a lot of transmission fluid in a modern car its
lifetime fluid you never need to change it then your ask an engineer what does a
lifetime fluid mean and an honest one will respond well it means that the
fluid is good for the lifetime of the transmission well ask about the warranty
is usually it's sixty thousand miles or something hey I don't want to
transmission that after sixty thousand or eighty thousand miles
goes out maybe the fluids go good theoretically but if the transmission
isn't shifting and you got to spend four or five grand for a new one or have it
rebuilt not a good idea my old Celica it's got two hundred
thirty thousand miles and the transformation still shifts like a dream
mind you I change the fluid every 30,000 miles not that big of a deal I don't
even worry about the filter and that's because these toyota designs a lot of
them don't have an actual filter they got a little screen just like a mosquito
screen on the windows of your house you just clean them you don't have to
replace them because there's not that much animal because realize transmission
fluid is cheap transmission rebuilds and new transmissions are very expensive you
don't want it to go this far you don't want a transmission that Revs way too
high before it starts shifting gears that's a no-no you don't want to
transmission that herky-jerky when it's taken off or slips when you're
trying to take off and you don't want to transmission that you put it in reverse
and you step on a gas and it won't move anywhere these are all signs that you
have a transmission problem you want to avoid this at all costs let's say you
let it get really dirty never changed it at all then if you try to flush it all
that crud is thrown through the systems as I said theoretically it sounds like a
good idea you'll flush all the crud out of the system and have brand new fluid
in but it often doesn't work that way not only because stuff can get clogged
up but an old transmission that's worn they are run by friction the fluid has
friction in it and the fluid friction helps the dynamics of making the car
move down a road guess what really dirty fluid actually has more friction in it so
if you change your transmission fluid by flushing it and you get all the dirty
friction fluid out put a new slippery shiny brand-new fluid guess what a lot
of times the transmissions will start to slip now to counteract that on it really
all transmission let's say the transmission needed a shift solenoid and
had to drop the pan real pro mechanics like myself they will save the old fluid
and put it back in so it won't have that problem now that might sound like a
stupid idea check out the old fluid replace broken
parts then put that old fluid back in got a car that's got 150 200 thousand
miles a lot of times that is the smarter way to go with that kind of mileage
you're off and living on borrowed time and your borrowed time and it goes way down to
nothing if you put in fresh fluid from really all dirty fluid so why does some
mechanics and shops tell you oh we're gonna flush your transmission fluid well
there's two main reasons for that and numero uno is it's a profit-making thing
it's like guys that say oh we have to power flush your injection system if
your car's running perfectly finding out no problems a lot of times that's just
over selling something to people and flushing the transmission fluid it's an
often oversold item and number two it's very easy for a shop to do it that has
the equipment you're gonna change the filter and fluid you got to drop the pan
a lot of the modern transmission pans don't even have gaskets they're glued on
and let me tell you it is a job getting that all glue off without breaking
anything you gotta hit and pry and pull it's messy you gotta buy a filter then
you got to fill it all back up but with the pressure machine automatic
transmissions have cooler lines on that go to the radiator or to a special
cooler all I gotta do is take those two lines off hook it to their machine and
flush it through it's a very easy thing for them to do with the equipment and as
most guys charge more money to flush a transformation then it just drop the pan
and change it they're making more money not a good idea to have an automatic
transmission flushed now yes you want to have clean fluid but if you change it
off and that's good enough yeah you're not changing at all you're changing some
of it but you're changing it off that if you keep doing it and if it has a filter
and you change that filter it's gonna get rid of any problems that you're
gonna have in the first place and that's especially true in modern cars because
the new cars most of them use a full synthetic fluid that fluid lasts longer
if you're just changing a bit at a time maybe a third at what's in it when you
just change the filter and fluid the old fluid mixed with the new fluid it doesn't
have the degradation that the fluids did when I was a young mechanic in the
60s and they just flat wore up plus the transmissions are so much better made
than they used to be back in a day almost all the American automatic
transmissions they had automatic clutches inside that's why we called
them automatic transmissions and they would shed a lot of clutch material and
that clutch material made of asbestos of course it's gonna clog stuff up well
they don't make them like that anymore so you don't have to worry about the
gross contamination that the older ones are getting if you didn't change them a
lot you're gonna have serious problems but today no the designs are better the
fluids are better so you should stay away from watching them now as far as
I'm concerned there's only one exception to this rule of not flushing let's say
you got a vehicle and it won't even go down the road or it slips so bad then
it's almost un-drivable what the heck if you want to take a
gamble somebody hooking up a machine and getting all the crud out of the system
especially an American automatic transmission you might give it a try if
you say that hey it's gonna cost you three four grand to have a rebuilt
transmission put in and it's an old car that's all worn out and it's slipping
like mad or doesn't even move what the heck you might give it a try just to
see if it'll work and sometimes it will work I'll say 25-30 percent of the times
that I've seen it happen like that they went back to at least drivability
they could go down the road okay maybe they still slipped a little or they
clunk a little but you could actually drive it one before the flush you
couldn't but that's an extreme case of an extreme junker worn-out vehicle don't
think that if you got a modern vehicle that's got 60 70 thousand miles and it's
a poor design and transmission slipping or shifting weird that flushing is going
to help that at all because realize that automatic transmissions are very
complicated and very sensitive to fluids differential pressure to the friction
that's inside them it's not like engine oil okay you're driving a car your
engines firing gasoline explosions there's all kinds of after-effects of
the burning and water vapor that get into the oil and contaminated so that's
just got to be changed at least once a year or every five six thousand miles in
most cases and yes modern automatic transmissions they're sealed units get
on that explosions and water and stuff going inside them they are sealed as
long you don't go under water and air from the transmission bubbles out water
takes its place when it's underwater because there isn't the build-up like
there isn't an engine but over time you don't get some build-up just from
friction things wearing pieces coming off inside so you do want to change the
fluid cloud maybe every 60,000 miles or something in a modern car but please
listen to scotty don't get suckered into being sold a transmission flush job
because then you ain't need a transmission overhaul job shortly after
that you just weren't prepared for especially if you had a transmission
that shifted perfectly fine in the first place and then it's starting to act up
after the fluid, so here the key to having a happy smooth
running transmission is keep it clean by regular oil and filter changing but not
by the radical process of flushing it with a power machine, so if you never
want to miss another one of my new car repair videos, remember to ring that Bell