Transmission Flush

[CRC2362]

Hey everyone, I need some advice about having the transmission serviced. My 99 DeVille has just over 50,000 miles on her and the maintenance schedule book states I'm due for service along with the dealer telling me it's time too. I have done a lot of reading on this, both from this great site and other sources and I have to admit there is a lot of confusion. Of course we all know what the dealer has said but many others have said that having transmission hooked up to one of those "flushing machines" is asking for trouble and that you should only have the pan dropped and change the filter. Please is there anyone out there that can shed some light on this subject? The car is running great, it shifts very smoothly as far as I can tell. Thanks

Craig

[Cadillac Jim]

Follow the dealer's advice. I have mine flushed every 30,000 miles. I prefer the dealer to do this job.

[OynxSTS]

Big mistake... Not a neccessary service... does more damage then good...

As per the owners manual change the tranny fluid at 50,000 miles only if...

Change automatic transaxle fluid and filter if the vehicle is mainly driven under one or more of these conditions:

In heavy city traffic where the outside temperature regularly reaches 90°F (32°C) or higher.

In hilly or mountainous terrain.

When doing frequent trailer towing.

Uses such as high performance operation.

If you do not use your vehicle under any of these conditions, the fluid and filter do not require change until the message CHANGE TRANS FLUID appears on the Driver Information Center.

[BodybyFisher]

Drain and refill based on the schedule in your owners manual. Never FLUSH.

[Ranger]

Here is what our old Guru (A GM powertrain engineer) had to say about it.

"Transmission Flushing - Good or bad?

Never, ever flush a transmission. There is no "safe" way to flush a transmission unless you own the flush machine and control it yourself.

Flushing a transmission has several pitfalls...

The most obvious is that the last vehicle hooked up to that flushing machine probably was on it's last leg and was generating tons of debris. Most owners, when the transmission starts to act up, rush to get a "flush" in the fervent hope that it will cure the problem. So... flush machines, by definition, see the worst of the worst. If the lines aren't cleaned, hooked up improperly, oil is reused or recycled, etc....then you are screwed as your transmission gets the dose of debris from the last transmission . No matter how good the intentions of the shop, one simple mistake and your transmission gets the debris.

Flushing is supposed to negate the need for removing the pan, cleaning the debris and replacing the filter... BS. There is considerable debris coating the inside of the transmission pan with miles as anyone who has done this can attest. That is part of the maintenance, removing the pan, cleaning the screens and replacing the filter and cleaning the pan.

All that debris in the pan is laying around in areas where there is little oil flow by definition... it tends to settle in the areas where the oil is quiet and just lies there not hurting anything.... until the "flush" stirs it up and circulates it thru the transmission. What a concept...

Reverse flush????? What logic makes anyone think that it is a good idea to reverse the oil flow path in a reverse flush and flush sediment and debris into areas that are normally protected by filters, etc...???? Stupid idea. Period. No other way to describe it.

"Transmission flush" machines are money makers for the shops and dealerships because they are quick and easy and they can actually charge more money for it under the guise of it being "better" for the transmission... when it is really a detriment.... suckers are born every day...

Read the factory service manuals and point out the place where a transmission "flush" is recommended.

So what if all the oil cannot be removed. A "flush" doesn't remove it all either.

If you really really want to replace as much oil as possible in the transmission, drain the pan, service it by removing/cleaning/changing the filter and reassemble. Refill the transmission with fresh fluid. Disconnect one of the cooler lines at the radiator, put it into a bucket and start the engine. Let the transmission oil pump purge the old oil into the bucket so that nothing is subjected to abnormal oil flow. Start pouring oil into the transmission to keep it full while the idling engine/transmission oil pump purges the fluid thru the system. Easy and quick and gets ALL the fluid out... and eliminates any risk of hooking up to a "flush machine".

I know this is about 4.1/4.5/4.9 engines but be aware that on the Northstar engines/4T80E transmissions there is a hidden drain plug for the transmission side cover that requires that the bottom pan be removed to drain the side cover oil storage area. The idea of flushing a 4T80E is even more ludicrous than a 4T60 transmission for this reason.

The 4T60 and 4T80 transmissions are similar in that both store oil in the side cover...but they do it differently. The 4T60 transmission with the 4.x engines stores oil in the side cover only when HOT. There is a bimetal thermostatic valve that closes causing side cover oil to be trapped behind a weir or dam. So, change the oil in a 4T60 transmission when it is cold to get the most oil out... The 4T80 transmission is a dry sump unit that ALWAYS stores it's oil in the side cover. There is a scavenge pump that scavenges the oil from the bottom pan to the side cover all the time. That is why there is a hidden drain plug underneath the bottom pan to drain the side cover when the pan is off for service.

FORGET THE IDEA OF FLUSHING YOUR TRANSMISSIONS. Normal transmission maintenance is a good idea. Drop the bottom pan, change the filter and clean everything up and refill the transmission with fresh fluid. Do the cooler line/bucket purge if you are really fastidious about changing all the fluid... but... DO NOT hook your transmission up to a flush machine.

Really now, would you get a blood transfusion from an unknown source that is reusing needles... about the same thing if you think about it. A flush will do absolutely nothing more than a good drain and refill will accomplish... and potentially a lot of harm. Do not take the risk. Just because some have had good experiences (or the lack of a bad experience) with a flush does NOT mean that they will always go good."

[Cadillac Jim]

Uses such as high performance operation.

Who, me?

I think I'll go with BodybyFisher. And, I'll keep servicing the transmission every 30,000 miles IAW the owner's manual caveat about high performance operation. They don't define what that means, so I'll put my lead foot forward here and say better safe than sorry.

[MAC]

Here is what our old Guru (A GM powertrain engineer) had to say about it.

If you really really want to replace as much oil as possible in the transmission, drain the pan, service it by removing/cleaning/changing the filter and reassemble. Refill the transmission with fresh fluid. Disconnect one of the cooler lines at the radiator, put it into a bucket and start the engine. Let the transmission oil pump purge the old oil into the bucket so that nothing is subjected to abnormal oil flow. Start pouring oil into the transmission to keep it full while the idling engine/transmission oil pump purges the fluid thru the system. Easy and quick and gets ALL the fluid out... and eliminates any risk of hooking up to a "flush machine".

I don't think service stations are required to accept used transmission fluid? So where can we dispose of used fluid in an environmentally safe way?

[JimD]

The closest aftermarket parts store to my house is Advance Auto. Their oil recycle tank says motor oil or transmission fluid accepted.

[BodybyFisher]

Also don't forget that the 4T80E tranny has a second drain inside the pan that must be opened and drained.

Tranny Drain Plug text, see photo 2

[OynxSTS]

Uses such as high performance operation.

Who, me?

I think I'll go with BodybyFisher. And, I'll keep servicing the transmission every 30,000 miles IAW the owner's manual caveat about high performance operation. They don't define what that means, so I'll put my lead foot forward here and say better safe than sorry.

You might want to re-read Body by Fisher's post...

Never FLUSH

As you will have read...

a) if you're flushing this transmission this is not a good idea... And not the right way to do this...

b ) fluid change at 30,000 is almost twice as often as you need to, even if you are driving 1/4 mile at a time and

c) Transmission fluid, unlike motor oil does not get "dirty" the same way motor oil does... The limiting factor to its life span is its temperature... Not mileage...

Dealerships are in existence to make money... They will do everything they can to talk you into services that your car doesn't need.

Its your money and if this makes you feel better about your car, go for it...

But do it with the knowledge that this really will not achieve anything...

PS the change trans oil message that our cars can generate is based mostly on how long the transmission had run under "over heat" conditions... Like the OLM it is fairly reliable.

[GreenMachine]

If I recall the manual (at least for the 98 Deville) states that if:

you drive in heavy city traffic where the temperture regulary exceed 90F

-In hilly or montain terrian

-Frequent trailer towing

-Taxi, police, delivary etc

....then you need to do it 50,000 miles or X number of months, or when the Change Trans Fluid message appears, not sure where the 30,000 mile number comes from.

Also my Factory Service Manual states that you should change the fluid AND replaced the filter (screens, apparantly theres internal filter that doesn't need replacing unless overhauling) at those intervals, flushing, if anything, only stirs that stuff up and may clog the filter or even worse force the gunk back into the system.

It does however mention "flushing" the Transmission cooler using the flow lines and letting them get all claned out.

I don't think service stations are required to accept used transmission fluid? So where can we dispose of used fluid in an environmentally safe way?

As a last resort flushing them down your toilet (or down the sewer) can be done. DO NOT however ever put anything down the storm drains.

At leat thats what I told by the town department as that "waste water" is treated and the storm drains are not.

[OynxSTS]

I don't think service stations are required to accept used transmission fluid? So where can we dispose of used fluid in an environmentally safe way?

As a last resort flushing them down your toilet (or down the sewer) can be done. DO NOT however ever put anything down the storm drains.

At leat thats what I told by the town department as that "waste water" is treated and the storm drains are not.

This varies city by city.... some of the older cities in North America still have combined storm and sewer systems and both water is treated... But OMG I can not imagine ANY City manager ANYWHERE telling you to flush new or used transmission fluid down the toilet.

Your sewer treatment system is designed to remove as much "bio-solids" (AKA ploppies) from the waste water... It is not designed to remove excess amounts of oils or industrial chemicals. In fact large quantities of simple cleaning chemicals are strong enough to kill all of the helpful bacteria that are used to perform secondary treatment.

What you should do, is take the use oil (motor, transmission, etc) to any shop that changes oil, local walmart, corner garage, quickie lube, etc and let them recycle it properly. This too varies state by state and province by province but in most places they are required to take it at no cost.

[BodybyFisher]

I would never dump oil or tranny fluid down the toilet or storm drain under an circumstance.

[chazglenn3]

I was told that you could pour antifreeze down the toilet...that also sounds like a bad idea to me, but the auto stores don't offer recycling for it that I am aware of.

Charles

[MAC]

I found a State of New Jersey website which lists recyclables and classifies them, and provides a list of dropoff points for each classification. In New Jersey, motor oil, transmission fluid, and antifreeze are considered Class D recyclable materials and must be disposed of by brining them to an authorized disposal location. I spoke to a municiple representative where I live and was told that used antifreeze cannot be flushed down the toilet. The State's "Clean Water" website is also a good source of information regarding recyclables.

I also have disposed of antifreeze by flushing it down the toilet. I was told years ago that toilet flushing was allowed. From now on, I will bring used antifreeze to an authorized disposal location.

[JohnnyG]

I have to admit there is a lot of confusion

What confusion? Only one person has recommended changing the fluid before the time stated in tha manual, and NOBODY has ever recommended the flush machine (except the dealer looking to make a quick buck of course!)

[KHE]

I bring my used antifreeze to the local Valvoline oil change store - they take it at no charge but require your name and address for their records.

[Fretbuzz470]

Ok and in no way is this an argument of sorts just curiosity. It seams that the main reason for NEVER flushing is due to the fact its more expensive than a pan drop and you don't know the condition of the equipment or the last vehicles trans condition hooked up to the machine.

Now lets say that you are one of two mechanics ( the other mechanic being as maticulous as you are) that use the machine since it got brought into the shop new. You have seen the vendor of the machine clean it inside and out on a monthly basis including changing all internal machine filters. It is also cheaper for you to run this service as you only have to pay 5% over the bulk trans fluid per qt price. Is there another reason that a Trans flush should never be done on these STS transmisions?? Our machine has a window to show the trans fluid passing through and we are not alowed to stop the trans flushing until the fluid is all clean. Any advice or reasonings beyond the negatives I have stated abouve would be greatly appreciated not only for my STS (being that I am a virgin Caddy owner) but also for the Cadys that I service through my shop. I do actually care about our shops reputation and would hate to be making a huge mistake on our customers vehicles. Oh yeah btw the reason I am asking is my cost on a flush is $29.99 and I just picked up my 00' STS w/ 107,000 miles and want to do any PM items that should be thought about w/o knowing the vehicles full PM history. I will most definately just drop the pan if there is a reasoning behind it as I am not about saving a few bucks just to "F" things up worse. I've see the latter way too much in my field. Thanx all for your input and if NE of ya are in the Milwaukee WI area feel free to drop me a line and I'll hook you up on tires or whatever I can.

Jay

[JohnnyG]

I DO remember our resident Cadillac engineer advising against the flush for the reasons you stated. What I also remember is that when dropping the pan, unusual debris collected on the screen might be discovered, indicating a serious condition. This statement was made in light of the fact that most people DO NOT EVEN CONSIDER transmission service until they have a problem. Therfore, 1 the flush will not fix the problem, and 2 the next guy that gets his tranny flushed will inherit the problem from him. This also assumes that most shops are NOT as meticulous as you on flush machine maintenance.

What I don't know is the flow rate through the side cover reservoir. A little unique feature of these transmissions. When dropping the pan, there is a seperate plug that must be removed to get the fluid out of the side cover, and as I recall, a substantial volume of fluid resides there. If this is a low flow area of the transmission, running the fluid through the flush machine until it appears clean, may not impact the quality of the fluid in the side cover area. This little reservoir of "not so good" fluid would then work its way back into the main body of the tranny in short order, defeating all of your efforts to flush ALL of the fluid out.

[MAC]

Read Ranger's post #5, which is written by a GM powertrain engineer. If you read it you will see that he goes into detail about why he would not recommend flushing a transmission.

[Fretbuzz470]

Ok so if I spend the lil extra money and drop the pan (clean pan out) change the filters, and pull the extra plug as well as the flush I should be OK. I just wana do things right and I am kinda a perfectionist (cept my spelling LOL)

[adallak]

Read Ranger's post #5, which is written by a GM powertrain engineer. If you read it you will see that he goes into detail about why he would not recommend flushing a transmission.

MAC,

What a beautiful Eldo! Looks like new.

[Ranger]

There are no filters to change. The filter is deep in the trans and only gets serviced during a complete overhaul. There are 2 reusable screens in the pan. The gasket is also reusable.

[BodybyFisher]

Read Ranger's post #5, which is written by a GM powertrain engineer. If you read it you will see that he goes into detail about why he would not recommend flushing a transmission.

I have been thinking the same thing MAC that is a beautiful Eldorado

[MAC]

Read Ranger's post #5, which is written by a GM powertrain engineer. If you read it you will see that he goes into detail about why he would not recommend flushing a transmission.

MAC,

What a beautiful Eldo! Looks like new.

Thanks adallak & BodyByFisher...And thanks to everyone who has complimented my Eldorado.