Draining from the tranny cooler line - safe or no?

[onion]

Ok smart guy. Remove the oil filter from your engine. Now start it and let the oil dump int a bucket. Is the engine getting lube oil?

A 'bucket flush' does essentially the same thing with an automatic transmission. The main difference being that MOST of the transmission isn't turning, so it probably doesn't matter much. But SOME of the transmission is turning. And lube oil isn't flowing.

Will it hurt anything? I dunno... don't really think so. But it's gonna take somebody who knows a whole [censored] of a lot more about transmissions than YOU do to give a credible answer.

 

[Jim Allen]

For the trannies I know something about, cooler line flow is about 10-15 percent of total lube flow, at most, and is at low pressure (relative to the other pressures in the trans). Cooler flow is just a small portion of the oil in the converter bled off for cooling. In some trannies, the cooler line oil comes back to lube & cool hard parts. In a few, it just dumps back into the pan. As I said, in the trannies I can look up here, the return oil goes to parts that are in operation or under load only when the car is moving, so the only potential damage I see is if the sump runs dry and the pump starves. That's easy to prevent if you keep the sump mostly full.

Boy, if the OP hasn't run screaming from this topic by now.....

 

[bmwtechguy]

Jim's explanation above is very good. The only risk I know of running one without pressure is on some chrysler units which may set a pressure code which can be erased fairly simply. And no, the lube system of a transmission is not that comparable to an engine, as regards flushing the oil. On an engine, it would be sorta like flushing the engine oil without the crankshaft or camshaft(s) turning.....now where's the harm in that?

 

[SteveSRT8]

absolutely nonsense to imagine this would hurt any auto box I've ever seen.

Nothing is moving except the pump and the converter, which is full of fluid. The instant you see cavitation you refill the pan. So the pump is not being starved, and there is still normal internal pressures. End of story for any normal auto box

 

[onion]

Originally Posted By: SteveSRT8
absolutely nonsense to imagine this would hurt any auto box I've ever seen.

Nothing is moving except the pump and the converter, which is full of fluid. The instant you see cavitation you refill the pan. So the pump is not being starved, and there is still normal internal pressures. End of story for any normal auto box


Don't forget the forward clutch. It's disengaged, and half of it is turning. How exactly is that bushing lubed?

I don't know the answer to that, and I imagine that it'll vary according to transmission design. Do you KNOW that the bushings for the foreward clutch hub/drum are not lubed by return oil from the oooler? Other parts of the transmission ARE lubed by said return oil in lots of transmissions... how can you be so certain that the forward clutch is ALWAYS an exception?

Like I've said more than once, I don't think any significant damage will be caused by a 'bucket flush'. But I see a [censored] of a lot of unwarranted certainty on the matter from people around here- backed up by nothing in the way of evidence. It's common knowledge that return oil from the cooler IS the lube oil for parts of LOTS of transmissions. How can ya'll be so certain that the forward clutch bushings (some of which ARE turning with the trans in park) are not among these parts that are lubed by cooler return oil?

 

[rslifkin]

It definitely does depend on the tranny. Some will be affected, others won't care at all.

 

[calvin1]

Originally Posted By: cp3
calvin1, how is sucking fluid out through the tube going to get more fluid? You wouldn't pull any from the converter would you?
If the trans is spinning then it's going to fill itself full of fluid. If it's off then it will partially drain into the pan. Whether you extract out of the dipstick or let it pump itself from the cooler line having the tranny running means less fluid can be taken out of the system.

 

[Jim Allen]

Originally Posted By: onion
But I see a [censored] of a lot of unwarranted certainty on the matter from people around here- backed up by nothing in the way of evidence. It's common knowledge that return oil from the cooler IS the lube oil for parts of LOTS of transmissions. How can ya'll be so certain that the forward clutch bushings (some of which ARE turning with the trans in park) are not among these parts that are lubed by cooler return oil?


No unwanted certainty on the cars/trucks I own, I can say because I have looked in the manual.

C6 Ford. '86 F250HD: Cooler flow lubes planetary gears. Forward clutch is lubed off the main pressure circuit.

BAXA Honda, '00 Accord V6: Cooler is at the very end of flow and dumps right into the sump. It appears everything gets oil prior to the cooler, so there should be no issue with a cooler line exchange at all.

4R75E Ford, '05 F150HD: I'm the least sure on this trans because the manual doesn't have a hydraulic flow chart perse, but indications are that cooler return goes to the rear of the trans. I'm less sure about forward clutch lubrication but on every Ford trans diagram I have seen, and GM as well, it's lubed off the main hyd circuit.

 

[lairdwd]

Originally Posted By: Jim Allen
BAXA Honda, '00 Accord V6: Cooler is at the very end of flow and dumps right into the sump. It appears everything gets oil prior to the cooler, so there should be no issue with a cooler line exchange at all.


Jim - do you know if that is also true of the 4 cylinder 2000 accord?

 

[Jim Allen]

Originally Posted By: lairdwd
Originally Posted By: Jim Allen
BAXA Honda, '00 Accord V6: Cooler is at the very end of flow and dumps right into the sump. It appears everything gets oil prior to the cooler, so there should be no issue with a cooler line exchange at all.


Jim - do you know if that is also true of the 4 cylinder 2000 accord?


Yes. My factory manuals also have the 4-cyl info and the hydraulic diagram is almost identical to the V6 but the fluid dumps right from the cooler into the reservior in both the 4 and V6.

 

[onion]

Originally Posted By: Jim Allen
Originally Posted By: onion
But I see a [censored] of a lot of unwarranted certainty on the matter from people around here- backed up by nothing in the way of evidence. It's common knowledge that return oil from the cooler IS the lube oil for parts of LOTS of transmissions. How can ya'll be so certain that the forward clutch bushings (some of which ARE turning with the trans in park) are not among these parts that are lubed by cooler return oil?


No unwanted certainty on the cars/trucks I own, I can say because I have looked in the manual.

C6 Ford. '86 F250HD: Cooler flow lubes planetary gears. Forward clutch is lubed off the main pressure circuit.

BAXA Honda, '00 Accord V6: Cooler is at the very end of flow and dumps right into the sump. It appears everything gets oil prior to the cooler, so there should be no issue with a cooler line exchange at all.

4R75E Ford, '05 F150HD: I'm the least sure on this trans because the manual doesn't have a hydraulic flow chart perse, but indications are that cooler return goes to the rear of the trans. I'm less sure about forward clutch lubrication but on every Ford trans diagram I have seen, and GM as well, it's lubed off the main hyd circuit.


Last time I got into this argument- a couple years ago- I looked up the hydraulic schematic in the factory service manual for my 4T60E. The schematic wasn't 100% clear, but like the example you cite, it appeared that the return oil from the cooler lubed only the planetaries. So in the case of that transmission and similar transmissions, I'm reasonably sure that a 'bucket flush' is a safe procedure.

But there are dozens of different makes and models of automatic transmissions out there. And without specific info, I would be hesitant to categorically state that a 'bucket flush' is 100% safe in all cases. Anybody can make that CLAIM... but backing it up is another thing entirely. We KNOW that cooler return oil is often used for lube. Is that lube oil required only for parts that turn while the vehicle is moving? We can be pretty sure of that in several common applications... but for all applications? That would be conjecture at best.

And as far as I'm aware, all professional transmission flush systems pump new ATF back into the cooler return line. If a bucket-flush was 100% safe and effective for all transmissions... why isn't it a common practice in the repair industry? Why are shops paying big $$ for completely unnecessary equipment?

 

[akmac]

Has anyone tried hooking another hose to the trans return line and putting it in a jug of new fluid? In this scenario the return on the tranny would have a hose hooked to it and that hose would be in a jug sucking in new fluid, while the output hose from the trans cooler would be pumping out old fluid into a waste container.

Have not tried this, but I'm planning to do it soon

 

[AzFireGuy79]

akmac-Return lines don't have any suction. Most drain back into the pan/sump and all others may drain to planataries which only need lube when the vehicle is in motion. This is why cooler line flushed( two quarts pumped out, stop engine, refill and repeat is perfectly ok. The pump gears are always drawing fluid. No other lubrication is required as the car/truck is stationary.

Onion- the reason most shops and OEM's don't use the cooler line purge method is due to the fact that you can hook up the T-tech and walk away. It does everything besides hook itself up and fill its chamber with ATF. No need to start and stop the vehicle and have an assistant. Much less mess....... There is no way a transmission will be damaged using the cooler line purge method. Amsoil even has the procedure on its site for the DIY'er. Needless to say, I have done countless cars and trucks with all sorts of transmission design, without issue. Why do you feel the need to scare people??? I would venture to say you haven't ever rebuilt a transmission. You look at several diagrams and draw a flawed conclusion. How about you show me some examples of cooler line exchanges gone bad.......

 

[onion]

I'm not about to get into a [censored] contest here, but suffice to say that I've overhauled more transmissions than most people have ever seen. Most of my transmission experience is in agricultural and construction equipment... I can count the number of automotive transmissions that I've rebuilt on one hand. I'm not claiming to be a transmission guru, but neither am I a neophyte.

I've never claimed that a transmission WILL be damaged by a bucket-flush... I've just expressed doubts about the certainty with which it's claimed around here that a bucket-flush CAN NOT damage a transmission. It's a mighty big claim, and one that can only be supported on a case-by-case basis (there are LOTS of transmission designs out there). Parts of the transmission ARE turning while the engine idles in park.

The question remains: how are the bushings in the forward clutch lubed? On the schematics that I've looked at for GM transmissions, I'm fairly confident that cooler-return oil only lubes the planetary gears. Others in this thread are similarly confident about Ford and Honda transmissions. What do we know about Mopars? Subarus? Hyundais? etc. etc. Unless you've seen the proof that this is a safe procedure, you're making a pretty big assumption... one that could potentially damage said transmission.

And seriously... AMSOIL's site is being cited as evidence? The same company that recommends their ATF for every transmission under the sun, claiming to cover widely varying and even contradictory specifications? Spare me.

 

[SteveSRT8]

Man, that's some axe you have to grind there.

The key point is if you understand the fluid flow charts, the cooler only receives a portion of the fluid output, not all.

So as long as the pump is not operated dry then absolutely NOTHING goes unlubed. So what's to worry about?

Hey, any procedure carries risk, even using the stupid passive machines. I owned a B&G for a long time. It was nothing but a bladder and a reservoir! That's it. It's main value was the impressive rack of adapters to connect with almost any trans line.

 

[My442]

IF you can put new fluid in at roughly the same rate it is coming out, then there is little to no chance that damage will occur.

How to do that is the tricky part.