Transmission Fluid Flow Rate through Radiator problem?

inefficient torque converter. On long highway drives this should not happen if the torque converter lockup clutch is working.

Thanks Mike, Now this sounds really interesting. It was my torque converter that was really shot before I had it (and the tranny) rebuild.

I will ask the tranny shop if we have a chicken & egg situation here. Torque converter causing heat... or even low t-fluid flow that causes the torque converter to not cool and thus over heat.

Thanks Dave-in-Denver

Without knowing how much cooling capacity the auxiliary cooler has, I would not recommend permanently disconnecting or bypassing the radiator.

inefficient torque converter. On long highway drives this should not happen if the torque converter lockup clutch is working.

Most cooling loops work like this:

Fluid from pump goes to torque converter. From torque converter it goes to the cooler. From the cooler it goes to bearings and other similar tasks.

Some fluid from the pump is bypassed to run the controlling servos and valves. That fluid is dumped back into the pan.

Any aux cooler of sufficient capacity will work just fine, you don't need the one in the radiator. IIRC the original post said this was a small(er) truck, right? ANd if you are worried about AFT temperature, get a temp guage installed and monitor the ATF temp in the pan. (No, there is no use in monitoring the ATF temp to the cooler, as that reflects the heat from the torque converter...) Measure the pan ATF temps. Ideally as cool as possible.

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.

PeterD wrote in news: snipped-for-privacy@4ax.com:

I am sorry but you are so wrong. the fluid goes from the cooler right back into the pan. Also the big trucks use a thermostat in the cooler so the fluid does not get over cooled. The reason the rad is suppsted to always be after the aux cooler is to prevent overcooling in colder weather. KB

Nope, I can prove it, though we both could be right as there may be some that do go from the cooler to the pan. But not all transmissions do so.

Rarely. If ever. Cite one vehicle for me... The Hummer H1: no thermostat. Dodge 2500 Hemi: no thermostat. Oh, and the Hummer H1--ATF from the cooler lubricates the bearings, and rate of flow is critical to longevity of the transmission. So critical that there is a bypass valve in case back pressure builds up to an unacceptable level.

Unlike engine oil that must achieve a certain temperature (to boil off water and other volatile elements) ATF need not reach any specific temperature. That being the case, the lower the ATF temperature, the longer lived is the transmission.

Some new info...

Tranny shop ran a flush cleaner machine on the radiator all night. When they looked at it this morning its flow improved only a very small amount... sill not much more than 1 quart in 30 seconds. That translated to just 1/2 Gallon Per Minute (GPM).

Tranny shop said that 0.5 GPM is just way too low... plain and simple. It should be in the 1 to 5 range. They were not particularly interested in spending the time finding out what the engineers and spec sheets say or in measuring the in/out temps. They said the flow rate test of the radiator failed BADLY and since the overnight flush cleaner did not find/fix any clogs then the next practical step to replace the radiator (close to $300 for P/L,etc). Then they will test flow and temps again... and send me home.

Tranny shop is also going to inspect and replace the inline filters, drop pan and inspect it for debris, and of course take care of the tranny filter itself. They have a 3 year warrantee (rebuild was a bit over 6 months ago) and will perform annual inspection and tranny service at 12, 24, 36 months for free to keep an eye on it.

This sounds reasonable to me (assuming they do not just scoop out pan debris every year and send me on my way).

What do you all think?

Thx Dave-in-Denver

Get an auxiliary cooler big enough to handle the HP your vehicle is rated for and then a little more. Use that instead of your in-radiator cooler. See what happens.

Have you thought about using a bypass filter in the cooler lines?

nate

Peter, Kevin, You guy are way out of my league.

One item of information that my brain has hung on to from 6+ months ago when I was shopping for a tranny shop....

An owner of one of the shops told me that the viscosity of t-fluid is very sensitive to high temps. And once a certain temp is reached, what ever the reason is and which is usually not much above where the idiot temperature light switch is set, that the resulting heat from viscosity/lubrication failure can become a run away problem and the tranny is cooked.

He said when a tran temp light comes on it is critically important to get you foot out of the gas, baby the thing out of the way, and just sit with motor running to circulate/cool the t-fluid.

FYI... that is what I did when I recently got my high temp warning.

Thx Dave-in-Denver

Yes I thought about something like what you mentioned back 3 years ago when I first put on an aux cooler to try to extend the life of tranny that I knew was doomed.

But none of the tranny shops liked the idea of completely bypassing the factory designed. Tranny shops were only willing to ADD to what the factory had by adding an cooler in-line (and as a few other posters have stated) but that is all. I would have to either do it my self (no talent or time) or take it to general repair shop to "modify" rather than "augment" the t-cooler setup.

Thx Dave-in-Denver

I don't know that I agree with them (I've not heard that it is bad for the trans to run too cool, unlike an engine where that is definitely true) but if it bothers you, you could use an oil cooler thermostat to regulate the temperature of the transmission oil. Unfortunately, that would probably approach the cost of another new radiator.

Alternately, I wonder if anyone makes add-on oil-to-water heat exchangers anymore? That would pretty much fulfill the same function as a trans cooler in the radiator; you'd have to splice into a heater hose or a radiator hose though.

nate

1 qt in 30 seconds is about half what it should be...

inefficient torque converter. On long highway drives this should not happen if the torque converter lockup clutch is working.

sure it is engaging. The lockup clutch is a mechanical clutch and is used to increase fuel mileage by eliminate torque converter slippage. If the lockup clutch is engaged (on most vehicles only in the highest gear) there should be little heat generated by the transmission.

inefficient torque converter. On long highway drives this should not happen if the torque converter lockup clutch is working.

Thanks Mike, Your comments sound exactly like one of the things the tranny shop found wrong 6+ months ago when they rebuilt the TC and tranny.

So I will ask them about this when we do our test drive after we put in the new radiator.

Thx Dave-in-Denver

Thanks Peter! Yep, your are correct.

I just found out this morning that the capacity specs on my radiator for the t-fluid flow is 3 to 7 GPM, depending on the power of the transmission fluid pump.

3 GPM = 6 qts in 30 seconds. A far cry from my 1 quart in 30 seconds.

Now I know that engine RPM and tranny RPM certainly (one of those two) impact the t-fluid rate of flow and to be precise we should state GPM at a some specified RPM. But since we are now certain the radiator is restricting the flow... we have identified our bad guy.

Thx Dave-in-Denver

Dave,

I don't have time to read over all of the messages in this thread, but I will chime in anyway, possibly adding nothing of importance...

I would like to know what you mean by "overheats". Do you mean that the trans temp light comes on at a certain point in your drive?

If so, I would be suspicious of the ATF level. If it is a hair too high in a A340F transmission/transfer unit, the fluid will readily aerate and cause that symptom. I would also be suspicious of what fluid additive a trans shop uses. They are often not as knowledgeable about transmission practice and theory as one would expect.

The original equipment aux cooler is very small, but it is adequate for any use I have run across. One problem with it is the location; a careless butcher can easily rack the left front lift arm on it and crush it trying to lift the vehicle. Has this cooler been bypassed in favor of an aftermarket one? If so, is the aftermarket unit inline with the airflow created by the mechanical fan?

I do agree that your original flow specs through the radiator cooler sound low, but that is a guestimate based on other similar experiments I have done at work, not your exact test.

Toyota MDT in MO

Hi Toyaota MDT,

I have inserted comments.

Yes... the tran temp light comes on. When doing 60+mph for about an hour.

Yes we found that we were way over filled... about 1.5 inches over the high mark. And yes a Toyota guy told me that too much fluid would aerate the t-fluid leading to overheating. I told this to tranny shop... was certainly unhappy that his guys overfilled the tranny but was skeptical that overfilling would cause tran temp light issues at just 60mph. So he did some checking and found the raidator had low t- fluid flow.

I do not know what t-fluid product they use. I was not in a position to have an opinion then... but now I know that what the Toyota guy told me; Dex2 is what that 1993 4Runner tranny was designed for... Dex3 replaced it a long time ago and on "really long multi-hour drives there is sometimes a problem". He suggested Texaco havelin AFT as most problem free product.

My 93 4Runner just had radiator t-fluid cooling. I had a shop put in an aux cooler a few years ago when I first noticed tranny waring signs. Size? I let the shop pic it out and they located it above the skid plate... no extra fan.

So thanks for your comments/questions... all things I will cover the tranny shop owner on Monday.

Thx Dave-in-Denver

95 4Runner, V6 3L, Auto, 4x4. I had a trans overheating problem also. After a heated discussion with my dealerships service manager, where I told him that my trans was overfilled and I thought that was my problem, he called Toyota. The fix was to check and make sure the trans was not overfilled. It needs to be checked after idling for 15 minutes. If it's overfilled it will cause the clutches to slip and overheat. On my last service they had overfilled it. They changed the fluid and filled it to the correct level and the problem went away.

Ron

Ron

Hi Ron, I think you are right... glad to have found someone who has the same picky tranny. If tranny fluid level was spot on... may never have found or noticed the poor flow problem.

The overfilled tranny was an important part of the problem. Then layer onto to that Dex2 vs Dex3 issue, then finding my radiator had restricted flow in it t-fluid section. This all did add up to some finger pointing... all had some ownership of the problem.

Thx Dave-in-Denver