Transmission Fluid Flow Rate through Radiator problem?

Even if there could be a long-term durability issue with running the trans "too cool" (which I honestly have not heard of) I don't see any problem at all with running it solely through an aux. cooler for a couple weeks simply to see if the overheating issue returns. If it does not, it would appear that your flow restriction is indeed the issue.

good luck,

nate

The problem with running the transmission solely on the auxiliary cooler is not that the transmission fluid would be too cool. The auxiliary cooler is just that - auxiliary - and not intended to be the primary or sole cooler. Without knowing what the expected temperature of the fluid coming out of the transmission is, and how much heat needs to be dissipated, there is no way to predict whether the aux cooler has sufficient capacity to serve as the sole cooler.

While the radiator can be bypassed and the fluid run through the aux cooler as an experiment, the fluid temperature would have to be closely monitored using a temp gauge of some sort. Of course, one has to know what proper output temps should be in order for this experiment to have any merit and to avoid the risk of transmission damage.

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

Actually it can in winter. THe raditor warms fluid up because heat discharge circulates through tank where cooler is so even if core is cold, the tank end can be warmer.

----------------- TheSnoMan.com

I understand that theory, but I see no other source for the problem you are having. Either dump the radiator for a new one, or bypass it and use the aux cooler all by itself.

You are getting only one-third of the required flow when the radiator is in the system. Take it out and get all of the flow that is available.

At this point, it is way better than the radiator. The aux cooler with cold air blowing across it has got to be at least as efficient as the single tube that is surrounded by hot water. If the OP was dragging a trailer over the Continental Divide or across the Arizone Desert in the dead of summer, then I'd agree that the capacity of the aux cooler would be important, but if the usage model he has is simply driving to work, then the aux cooler ought to be fine.

But, you're right. We don't know the capacity of the aux cooler. We do know that the capacity of the radiator is severely compromised ...

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

Ron, He has confirmed that the fluid does not flow efficiently through the radiator.

Hi Jeff, Yes... my radiator will only flow 1 quart in 30 seconds (a third of what the tranny fluid pump wants to push) and that it did not improve after spending the nigh on the flush/cleaner machine.

4Runner is still in shop... owner working on this himself on a hit/ miss basis rather than one of the his usual guys. So tomorrow he expects to tell be result of the flow test through a NEW radiator.

Thx Dave-in-Denver

Picked up 4Runner yesterday with new Radiator (and same aux cooler). T-fluid Flow rate through the radiator was great... "over a gallon in less than 45 seconds" according to the shop owner. (Wish he had done an apples to apples time/volume test... but the flow was "so huge" compared to the bad radiator the tranny shop knew the problem was solved.

AND they did not overfill it... in fact the t-fluid levels are at the mid mark on the dipstick... not the high mark.

I have a 6 hr drive in the mountains tomorrow with temps in 80's... will be a good test.

Thx Dave-in-Denver

Thx for the feedback... Ron

No OVERHEATING TRANNY!!!

Drove 300+ miles yesterday in the Colo mountains and not one blink from the Tran Temp Light. So the radiator was in fact the the bad guy.

Checked fluid level 6 times. Had everything from half an inch under the low end of the "hot range" on the dipstick to half an inch over the high end of the "hot range".

- The highest level was observed one block from the highway after a hard fast mountain pull.

- The lowest level later observed was later in day on the return trip home after power costing nearly an hour back down into Denver.

Thanks to everyone for there comments/suggestions!

Dave-in-Denver