Confused - should I flush or not?
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Senior Member
Joined: Jan 2014
Posts: 355
From: Central Fla
Confused - should I flush or not?
I got my 2008 H3 in Feb. from a ford dealership. The dealership replaced radiator, tires and I think fuel pump (I think). Now I did not ask about if tranny or oil was done, I am thinking yes on oil with cheap oil and maybe not the transmission.
I have no issues with the vehicle and it has decent pickup.
So I am thinking (on even numbered days) don't fix what's not broken. Then (on odd numbered days ) I am thinking, put full synthetics in there and treat the vehicle as best as possible.
I read "don't flush the transmission as the new fluid is like a detergent and will cause problems".. Something like that. Then I read some people flush every 30,000 miles, and things are great.
So, my h3 has 68k miles on it, and I mostly do city driving. Should I replace oil and tran fluid or just oil or......should I leave tranny alone?
Advice welcomed
I have no issues with the vehicle and it has decent pickup.
So I am thinking (on even numbered days) don't fix what's not broken. Then (on odd numbered days ) I am thinking, put full synthetics in there and treat the vehicle as best as possible.
I read "don't flush the transmission as the new fluid is like a detergent and will cause problems".. Something like that. Then I read some people flush every 30,000 miles, and things are great.
So, my h3 has 68k miles on it, and I mostly do city driving. Should I replace oil and tran fluid or just oil or......should I leave tranny alone?
Advice welcomed
Senior Member
Joined: Sep 2008
Posts: 6,126
From: SE Michigan
Never been a "flush" guy. Drop the pan, replace the filter, replace the pan gasket, put the pan back on and fill'er up kind of guy. I could see a "flush" if you had some shifting issues. If nothing is wrong currently with your trans why do you need to "flush" it.
Just my $0.02.
Just my $0.02.
Senior Member
Joined: Jul 2012
Posts: 8,971
From: C-Town
When you drop the pan, you are not getting all of the old fluid out!
Pulling the plug on the engine, transfer case, & axles remove the old fluid so you can add all new fluid.
Unfortunately that does not work on a transmission, therefore the reason for a transmission flush (aka: fluid exchange).
I did mine with 16 new quarts(it only holds 11 quarts) making sure that the old came out and all new fluid is back in.
Pulling the plug on the engine, transfer case, & axles remove the old fluid so you can add all new fluid.
Unfortunately that does not work on a transmission, therefore the reason for a transmission flush (aka: fluid exchange).
I did mine with 16 new quarts(it only holds 11 quarts) making sure that the old came out and all new fluid is back in.
Senior Member
Joined: Jul 2012
Posts: 8,971
From: C-Town
Yes, All of it with Dex VI
How often should the automatic transmission fluid be changed?
Most owners’ manuals say it isn't necessary. Yeah, right. That's why transmission shops are
making a fortune replacing burned out automatic transmissions.
Why ATF Wears Out
An automatic transmission creates a lot of internal heat through friction: the friction of the fluid
churning inside the torque converter, friction created when the clutch plates engage, and the
normal friction created by gears and bearings carrying their loads.
It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in
motion. Normal driving will raise fluid temperatures to 175° F, which is the usual temperature
range at which most fluids are designed to operate. If fluid temperatures can be held to 175° F,
ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much
higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid
temperatures well beyond safe limits. And once that happens, the trouble begins.
At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt
toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins
to form on internal parts (such as the valve body) which interfere with the operation of the
transmission. If the temperature gets above 250° F, rubber seals begin to harden, which leads to
leaks and pressure losses. At higher temperatures the transmission begins to slip, which only
aggravates overheating even more. Eventually the clutches burn out and the transmission calls it
quits. The only way to repair the damage now is with an overhaul -- a job which can easily run
upwards of $2500 on a late model front-wheel drive car or minivan.
As a rule of thumb, every 20 degree increase in operating temperature above 175° F cuts the life
of the fluid in half!
At 195° F, for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly
encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240° F, the
fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to
5,000 miles. Go to 295 or 300° F, and 1,000 to 1,500 miles is about all you'll get before the
transmission burns up.
If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again.
According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission
failures are caused by overheating. And most of these can be blamed on worn out fluid that
should have been replaced.
On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the
bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop
of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself
may be running at anywhere from 180 to 220° F!
How often should the automatic transmission fluid be changed?
Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that
enters the radiator cooler at 300° F leaves at 240 to 270° F, which is only a 10 to 20% drop in
temperature, and is nowhere good enough for extended fluid life.
Any number of things can push ATF temperatures beyond the system's ability to maintain safe
limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather,
stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free
a tire from mud or snow, etc. Problems in the cooling system itself such as a low coolant level, a
defective cooling fan, fan clutch, thermostat or water pump, an obstructed radiator, etc., will also
diminish ATF cooling efficiency.
How often should the automatic transmission fluid be changed?
Most owners’ manuals say it isn't necessary. Yeah, right. That's why transmission shops are
making a fortune replacing burned out automatic transmissions.
Why ATF Wears Out
An automatic transmission creates a lot of internal heat through friction: the friction of the fluid
churning inside the torque converter, friction created when the clutch plates engage, and the
normal friction created by gears and bearings carrying their loads.
It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in
motion. Normal driving will raise fluid temperatures to 175° F, which is the usual temperature
range at which most fluids are designed to operate. If fluid temperatures can be held to 175° F,
ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much
higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid
temperatures well beyond safe limits. And once that happens, the trouble begins.
At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt
toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins
to form on internal parts (such as the valve body) which interfere with the operation of the
transmission. If the temperature gets above 250° F, rubber seals begin to harden, which leads to
leaks and pressure losses. At higher temperatures the transmission begins to slip, which only
aggravates overheating even more. Eventually the clutches burn out and the transmission calls it
quits. The only way to repair the damage now is with an overhaul -- a job which can easily run
upwards of $2500 on a late model front-wheel drive car or minivan.
As a rule of thumb, every 20 degree increase in operating temperature above 175° F cuts the life
of the fluid in half!
At 195° F, for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly
encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240° F, the
fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to
5,000 miles. Go to 295 or 300° F, and 1,000 to 1,500 miles is about all you'll get before the
transmission burns up.
If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again.
According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission
failures are caused by overheating. And most of these can be blamed on worn out fluid that
should have been replaced.
On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the
bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop
of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself
may be running at anywhere from 180 to 220° F!
How often should the automatic transmission fluid be changed?
Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that
enters the radiator cooler at 300° F leaves at 240 to 270° F, which is only a 10 to 20% drop in
temperature, and is nowhere good enough for extended fluid life.
Any number of things can push ATF temperatures beyond the system's ability to maintain safe
limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather,
stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free
a tire from mud or snow, etc. Problems in the cooling system itself such as a low coolant level, a
defective cooling fan, fan clutch, thermostat or water pump, an obstructed radiator, etc., will also
diminish ATF cooling efficiency.
Junior Member
Joined: Dec 2011
Posts: 17
From: florida
What's up Atari ?? Decisions decisions .here's what I did when I got mine from stingray Chevrolet in Tampa .I checked all the fluids and decided to change them all my front diff was dirty as hell and only had40000 Miles did rear as well also changed the transfer finally got to tranny decided to flush at 42000 & I will be doing a filter change about 85000 at 68000 you don't know what the person did with it previously so go ahead and change the filter and it will need about 6 quarts at least you'll know it's some what decent and down the road you can change it again .one thing you can do is pull the dipstick wipe it with your hand and smelll it if it smells burnt definitly change it if it's red and smells clean your probabley good .hope this long *** post helps
Senior Member
Joined: May 2008
Posts: 834
From: Blacksburg, VA
I too have done both. I did a pan drop at 30K and a flush at 60K. The manual says drop and drain. You will get a bunch of opinions on this and you will only get more confused.
Senior Member
Joined: Aug 2013
Posts: 136
Yes, All of it with Dex VI
How often should the automatic transmission fluid be changed?
Most owners’ manuals say it isn't necessary. Yeah, right. That's why transmission shops are
making a fortune replacing burned out automatic transmissions.
Why ATF Wears Out
An automatic transmission creates a lot of internal heat through friction: the friction of the fluid
churning inside the torque converter, friction created when the clutch plates engage, and the
normal friction created by gears and bearings carrying their loads.
It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in
motion. Normal driving will raise fluid temperatures to 175° F, which is the usual temperature
range at which most fluids are designed to operate. If fluid temperatures can be held to 175° F,
ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much
higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid
temperatures well beyond safe limits. And once that happens, the trouble begins.
At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt
toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins
to form on internal parts (such as the valve body) which interfere with the operation of the
transmission. If the temperature gets above 250° F, rubber seals begin to harden, which leads to
leaks and pressure losses. At higher temperatures the transmission begins to slip, which only
aggravates overheating even more. Eventually the clutches burn out and the transmission calls it
quits. The only way to repair the damage now is with an overhaul -- a job which can easily run
upwards of $2500 on a late model front-wheel drive car or minivan.
As a rule of thumb, every 20 degree increase in operating temperature above 175° F cuts the life
of the fluid in half!
At 195° F, for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly
encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240° F, the
fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to
5,000 miles. Go to 295 or 300° F, and 1,000 to 1,500 miles is about all you'll get before the
transmission burns up.
If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again.
According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission
failures are caused by overheating. And most of these can be blamed on worn out fluid that
should have been replaced.
On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the
bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop
of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself
may be running at anywhere from 180 to 220° F!
How often should the automatic transmission fluid be changed?
Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that
enters the radiator cooler at 300° F leaves at 240 to 270° F, which is only a 10 to 20% drop in
temperature, and is nowhere good enough for extended fluid life.
Any number of things can push ATF temperatures beyond the system's ability to maintain safe
limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather,
stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free
a tire from mud or snow, etc. Problems in the cooling system itself such as a low coolant level, a
defective cooling fan, fan clutch, thermostat or water pump, an obstructed radiator, etc., will also
diminish ATF cooling efficiency.
How often should the automatic transmission fluid be changed?
Most owners’ manuals say it isn't necessary. Yeah, right. That's why transmission shops are
making a fortune replacing burned out automatic transmissions.
Why ATF Wears Out
An automatic transmission creates a lot of internal heat through friction: the friction of the fluid
churning inside the torque converter, friction created when the clutch plates engage, and the
normal friction created by gears and bearings carrying their loads.
It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in
motion. Normal driving will raise fluid temperatures to 175° F, which is the usual temperature
range at which most fluids are designed to operate. If fluid temperatures can be held to 175° F,
ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much
higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid
temperatures well beyond safe limits. And once that happens, the trouble begins.
At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt
toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins
to form on internal parts (such as the valve body) which interfere with the operation of the
transmission. If the temperature gets above 250° F, rubber seals begin to harden, which leads to
leaks and pressure losses. At higher temperatures the transmission begins to slip, which only
aggravates overheating even more. Eventually the clutches burn out and the transmission calls it
quits. The only way to repair the damage now is with an overhaul -- a job which can easily run
upwards of $2500 on a late model front-wheel drive car or minivan.
As a rule of thumb, every 20 degree increase in operating temperature above 175° F cuts the life
of the fluid in half!
At 195° F, for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly
encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240° F, the
fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to
5,000 miles. Go to 295 or 300° F, and 1,000 to 1,500 miles is about all you'll get before the
transmission burns up.
If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again.
According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission
failures are caused by overheating. And most of these can be blamed on worn out fluid that
should have been replaced.
On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the
bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop
of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself
may be running at anywhere from 180 to 220° F!
How often should the automatic transmission fluid be changed?
Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that
enters the radiator cooler at 300° F leaves at 240 to 270° F, which is only a 10 to 20% drop in
temperature, and is nowhere good enough for extended fluid life.
Any number of things can push ATF temperatures beyond the system's ability to maintain safe
limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather,
stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free
a tire from mud or snow, etc. Problems in the cooling system itself such as a low coolant level, a
defective cooling fan, fan clutch, thermostat or water pump, an obstructed radiator, etc., will also
diminish ATF cooling efficiency.
Senior Member
Joined: Sep 2008
Posts: 6,126
From: SE Michigan
Automatic transmission maintenance intervals are given in your owner HUMMER owner's manual. I suggest following them,. The general intervals are designed to refresh the conditioners and detergents in the oil, and replace most of the oil which has thickened from heat with new oil. This also, of course, removes sediment when the pan is removed and cleaned and the filter is replaced.
Assuming that 1/5th to 1/3rd of the oil remains in the torque converter (I think that 1/3rd is a bit high), the sediment is still trapped in the filter and pan. Routine service intervals will maintain a healthy level of good oil in the transmission and help clean any deposits that may have formed. Most transmissions that have been regularly serviced show no deposits for this reason.
Flushing is a money maker for shops. Either they advertise that they "flush" the transmission and simply service it with new oil and filter, or they use a strong detergent to dissolve residue, mainly in the valve body. But since they use something other than transmission oil to flush (if they do so), then 1/3 of your transmission might be filled with detergent, not oil, when the thing is buttoned up. Or if they flush with tranny fluid, what's the point? If it really needs "flushing" due to a driveability problem, then make several short interval services, say 5,000 mile intervals or every oil change, and see if the fresh oil will loosen things up. If not, you probably need a valve body overhaul before things get really out of hand.
Since you don't know the history of the vehicle, I would simply follow normal service intervals unless you are having problems with the transmission. That should be more than enough to keep you out of trouble. If it ain't broke...
Assuming that 1/5th to 1/3rd of the oil remains in the torque converter (I think that 1/3rd is a bit high), the sediment is still trapped in the filter and pan. Routine service intervals will maintain a healthy level of good oil in the transmission and help clean any deposits that may have formed. Most transmissions that have been regularly serviced show no deposits for this reason.
Flushing is a money maker for shops. Either they advertise that they "flush" the transmission and simply service it with new oil and filter, or they use a strong detergent to dissolve residue, mainly in the valve body. But since they use something other than transmission oil to flush (if they do so), then 1/3 of your transmission might be filled with detergent, not oil, when the thing is buttoned up. Or if they flush with tranny fluid, what's the point? If it really needs "flushing" due to a driveability problem, then make several short interval services, say 5,000 mile intervals or every oil change, and see if the fresh oil will loosen things up. If not, you probably need a valve body overhaul before things get really out of hand.
Since you don't know the history of the vehicle, I would simply follow normal service intervals unless you are having problems with the transmission. That should be more than enough to keep you out of trouble. If it ain't broke...
Last edited by TAINTER; Apr 7, 2014 at 11:09 PM.