Transmission Fluid Flow Rate through Radiator problem?

Thanks Ray O, Tranny shop said they tested t-fluid flow with "operating temp" fluid using the same RPM's for three flow tests;

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

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

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

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

Pro info. Thanks SnoMan.

Dave-in-Denver

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.

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!

I am not familiar with the 'yota trans but, do not believe it would be grossly different from most of the others. The cooler is an orifice bleed from the pressure controlled side of the pump to the torque converter. The engine RPM should make little difference in flow but, flow will change with line pressure in the trans which can change for several reasons. There should be little restriction in the cooler circuit, and therefore, little pressure in the cooler system as it is simply dumped back into the trans sump thru the rear of the trans. Basically, the cooler circuit should have little restriction resulting in very low pressure. I would try having the radiator cleaned and reverse flushing the built-in cooler to improve flow. If the end caps are removed from the radiator, visually inspect the cooler for any dents or kinks. If you have flexible hoses in the cooler circuit, I would suspect deterioration causing internal swelling or other damage restricting the flow. It is not common for the radiator cooler to become blocked for no reason as the feed orifice in the trans is small and incapable of passing debris large enough to block the cooler circuit downstream.

Good luck

Lugnut

What transmission? The cooler flow rate is listed in the detailed specifications. As well, there is a test described for some transmissions (I can quote the 4L80E's test if anyone is interested). Low flow in the cooler can lead to premature failure due to lack of proper lubrication of some components.

Perhaps... Again, without checking the 'book' you don't know.

Get some vinyl tubing with the same inside diameter as the cooler, wrap it back and forth until it's about the same configuration as the cooler, and pour some transmission fluid through it. If the fluid comes out of the cooler much slower than your reference tube, something is clogged. If not, it's probably okay.

--scott

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

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

Return flow from AT coolers in automotive use generally (but not in every case) goes into the rear lube circuits of the transmission and NOT directly back into the sump. Cooler flow restrictions usually cause case bearing, shaft and planetary gear set failures.

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

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

From all of the post here including your info, the only answer seems to be (preferabley) replace the radiator which probably has a restricted cooler. If the caps come off, a good rad shop can do this and visually inspect for physical damage. If you find physical damage, you are then sure of the problem even though you have already isolated it to the part you know has to be corrected or replaced. Option 2 is to completely bypass the rad cooler to an oversize aux cooler. Use a stacked plate type cooler which inherently has a sort of temperature control as it normally flows better at higher temps. These are widely available and easy to install. Self install for largest unit should be under $100 even if they rip you a little. Summitt Racing and Jegs have decent online prices. If you are concerned about over cooling the trans, I can tell you I have never heard of a trans failure because of overcooling and I have never heard this from my parts supplier. Denver may be an exception in the winter but, I don't think so.

BTW, since you have already had a trans failure, it is entirely possible that debris from that failure made it to the cooler and can still be found there even though it looks like you now have a filter on it. The filter was added by the shop to protect the rebuild - not by the manufacturer. I don't know where the filter is but, make sure the line ends were not crimped when they cut it to install the filter. I have seen tubing cutters dull enough to actually swage the ends of the line more than enough to restrict flow. The shop needs to check to be sure the ends are not swaged.

Lugnut