Transmission Fluid Flow Rate through Radiator problem?

My new transmission is (still) overheating on long highway drives.
Transmission shop tested the t-fluid flow rate through the radiator at
1 quart every 30 seconds. The transmission itself however will push times that amount, 3 quarts every 30 seconds, all by itself and also through an aux t-cooler.
My radiator is only 2 years old. When I first started having transmission overheating I found the radiator was shot and had it replaced and later put in a tran cooler too.
So the questions is... What should be the t-fluid flow rate through the radiator? In other words... is my radiator restricting t-fluid flow rates below spec?
1993 4Runner, V6 3L, Auto, 4x4, 170K
Thx Dave-in-Denver
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I do not recall ever seeing a specification for transmission fluid flow rate through the radiator. The flow rate will vary depending on pump output. I would see if the coolant temperature drops after it exits the radiator and cooler.
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Ray O
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On Wed, 13 Jun 2007 16:00:45 -0500, "Ray O" <rokigawaATtristarassociates.com> wrote:>

I have not seen a flow rate either but I also agree the pump output will variy some with engine RPM and is not a fixed rate. As mentioned above the tempature drop is the bigger concern and if OP had over heating tranny problems if engine was running hot too it would take the tranny with it unless you had a aux external cooler. DO not get carried away with aux cooler size though as many do because you can overcool oil and reduce flow rate because oil is thicker when cooler. ----------------- TheSnoMan.com
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Thanks SnoMan, I will ask about the in/out temp drop.
Engine has never run hot... temp gauge rarely varies once up to temp.
Have to presume that OP in tranny has been pushing against what we presume to be a low flow problem in the radiator since the radiator was new 2 years ago, and since the new tranny was rebuild 6 months ago. (FYI the new tranny work Soooo much better than the old one and it still does.)
Aux cooler was picked out by tranny shop... it looks smaller than what I would have picked out... so my guess is that the tranny shop follows your advise too and does not over do it on aux size.
Thx Dave-in-Denver
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On Wed, 13 Jun 2007 16:08:29 -0700, snipped-for-privacy@gmail.com wrote:

One tip here on aux cooler, make sure it is routed so fluid passes through radiotr core tube and then aux cooler, not the other way around and not bypassing tank cooler completely either. ----------------- TheSnoMan.com
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Hi SnoMan, Well that is a good tip.
I was considering asking the tranny shop to skip the radiator (due to its poor performance) and just use the aux cooler.
Why not just aux cooler... is it because there is no fan or is it a simple volume thing. FYI... my aux cooler is down on the skip plate... no room (they said) to double up at the radiator.
Thx Dave-in-Denver
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On Wed, 13 Jun 2007 18:13:49 -0700, snipped-for-privacy@gmail.com wrote:

There is a couple of reasons. First water can take a LOT more heat from oil than air if coolant is cool and it also help stabile the oil temp and warm tranny up because heater recirculates water through tank where cooler is. Next is if you do bypass it you will reduce effectiveness of your A/C some because it dumps hot air on condensor so it cools it less. Logically to get best cooling for it you want the oil to be pre cooled in radiotr then cooled a bit more in aux cooler with throwing all the heat into A/C condensor. When routed in seris like that the aux cooler does not dump as much heat on AC and it also acts as a safty net should engine overheat, tranny still gets cooled. ----------------- TheSnoMan.com
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Pro info. Thanks SnoMan.
Dave-in-Denver
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wrote:

I only installed a cooler on one of my vehicles (but others have come from the factory with coolers already installed). On this one, the instructions said you could either install the cooler in series with the radiator cooler, in place of the radiator cooler, or in parallel with it.
I chose the first of the three options, but later came to believe this was not the best method. As another poster mentioned, any kink, bend or extra bit of plumbing will add to the resistance to flow in a hydraulic system. A parallel installation would appear to give the least resistance to flow, while a series installation would give highest resistance.
One thing I am not in doubt about is the critical nature of tranny temperature, and I would much rather have it overcool than overhot.
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Thanks Ray O, Tranny shop said they tested t-fluid flow with "operating temp" fluid using the same RPM's for three flow tests; 1) just tranny which produced 3 quarts in 30 sec. 2) tranny and aux-cooler which also produced 3 quarts in 30 sec. 3) tranny and radiator which produced just 1 quart in 30 sec.
Do not know if they had a measured both the in and out temps... will ask.
Have to presume their logic is.... if there is a restriction or fault in the radiator flow then the t-fluid will not cool... especially when the tranny wants a 3 quart rate.
Thx Dave-in-Denver
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If that is the case, then there is a problem in the radiator. The transmission part of the radiator may have been rebuilt incorrectly, the cooling fins are obstructed so that sufficient air does not flow through them, or something has clogged the cooler part internally.
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Ray O wrote:

???
Cooling fin damage or obstruction will not affect the flow rate through the unit.
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I agree that cooling fin damage or obstruction will not affect the flow rate through the unit, but it can reduce cooling capacity, which was the OP's original problem.
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Ray O wrote:

Gotcha.
Thought you were just commenting on the flow rate....
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My bad, yup, after re-reading my post, it does look like I was just commenting on the flow rate...
Thanks for pointing that out!
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Thanks Ray O, Yep... it sure points to a clog of some kind.
When I called Toyota... they had not tech info on t-fluid flow rate through the radiator.
But one thing is clear... the radiator is sure slowing down the flow and that can not be good.
Thx Dave-in-Denver
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snipped-for-privacy@gmail.com wrote:

Every turn in a line, additional cooler, fittings, ect, will cause some resistance in the hydraulic flow. Did the trans shop test the radiator flow bypassing the additional cooler? I have never seen a hydraulic cooler fail from the inside from corrosion, or buildup restrictions except for component failure that restrict/plug the line with debris. Make sure that the trans temp indicating system is operating correctly like Ray said. Check the temp with an in line gauge. Check the actual trans pump flow as well.
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Thanks Ph@Boy, Well the old tranny sure had it problems and your comments make me think that perhaps some debris from it could have caused the restriction in the radiator. And that junk was not cleaned out as part of the tranny job.... causing overheating and perhaps introducing old debris into my new tranny.... Yuck.
Good suggestion to test the tran temp sensor... I will ask.
Check the actual tranny pump flow... well I guess that the tranny shop was happy with the 3 quarts in 30 seconds... but I will ask them if it actually meets volume and SPI specs.
Thx Dave-in-Denver
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On Wed, 13 Jun 2007 16:16:53 -0700, snipped-for-privacy@gmail.com wrote:

This sounds high for a tranny at idle. Nominal flow rate would depend a lot on trany size and isle speed and oil cooler line size to. If you are really worried you could install a pressure gauge on tranny line in a "Tee" to test it. Check pressure before cooler and after and if there is a restriction in cooler you will see a big pressure differentail. ----------------- TheSnoMan.com
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Thx SnoMan, I sure hope the tranny shop owner has enough smarts to test flow at an RPM that is above idle... but you never no so I will ask.
Also... I like your idea (and others?) to actually check the pressure coming out of the tranny and not just observing the rate of flow. Will ask about this too.
Thx Dave-in-Denver
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