I don't know what the flow rate should be, but if you have installed an aux cooler, then you do not need to push the fluid through the radiator anymore, making the flow rate a moot point.
As a test, try connecting the transmission directly to the aux cooler, and leaving the radiator out of the circuit. If the transmission is pushing several quarts per minute without the radiator in line, and only 2 quarts per minute WITH the radiator connected, then leave the radiator disconnected ...
The diminished flow of fluid would certainly contribute to the overheating, so you are on the right track.
Thanks Jeff, My brain had this idea too... maybe on a temporary basis.
BUT... but another poster indicated that bypassing the radiator completely and just using the aux cooler would not be a good idea. What do you think about post #7?
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.
It is important as to what the vehicle is doing when the trans gets hot, but assuming normal loading and highway usage, the aux cooler should be more efficient than the radiator, especially if the radiator is clogged so badly that the flow is reduced by a factor of 3 or more.
There is much we don't know here, but if it was me having the trouble, I'd test the theory that the radiator is clogged by removing the radiator from the system. It should be easy enough to install some hoses that allow a direct connection of the transmission to the aux cooler without permanently altering the plumbing that is already in place. As part of the test, I'd simply connect both of the radiator hose bibs together so any fluid that might be inside the radiator does not come out and make a mess. Whatever fluid is there would be a small amount though, and any mess would be limited to the contents of the coils are inside the radiator.
Which poster said that? Utter hogwash, there is no reason not to remove the radiator cooling loop and use an aux cooler. Larger trucks have been doing that for years, and very successfully, too. Result is that the transmission runs *much* cooler (often times the radiator is heating the ATF, not cooling it!) and you get better flow rates.
BTW, what is post #7? Is that like love potion #9?
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.
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).
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?
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.
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.
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.
How much fluid flows out of the transmission all by itself? How much comes out of the radiator? How much comes out of the aux cooler?
If you get the same flow from the trans all by itself and from the aux cooler (without the radiator connected), and this amount is more than what comes out of the radiator, I can't see any problem with simply replacing the radiator again or bypassing it.
You could have pumped a piece of crap into the radiator that became lodged, and now the fluid won't flow like it should. (If this is true, the transmission guy should be able to hook the radiator up backwards to his Flushing Machine and blow fluid through it that will send the crap back out the way it came in.
If the radiator is the cause of the low flow (and the resulting heat build up), AND the aux cooler does not restrict the flow, then no matter what else is going on, the aux cooler is the only thing you should be using until you get the radiator repaired/replaced. If you want to get a larger aux cooler, then maybe that would be a good idea. I think your big issue now is to get your heat under control, and that is not going to happen as long as the radiator remains in the fluid path.
That last bit was a Guarded Statement, you need to determine where the flow becomes restricted, and cut THAT part out of the system, or fix it.
PS Lots of shops flush the transmission by simply hooking it up to a machine that pumps fluid through the cooling lines. They disconnect the trans from the radiator and hook a machine up to one of the lines, then pump juice in until what comes out is clean. They may or may not include the radiator when doing this, but there is no reason they could not JUST do the radiator. It would take more time to connect the machine than to run it, and if they used a clean bucket to collect the fluid that comes out, you could examine it easily to see if there was any crap in it.
The guy that does this could also surmise if the flow was restricted because he ought to know how fast he is pumping new fluid in, and old fluid coming out should be at the same rate. He should be able to tell if the fluid is coming out slowly or not. If it is coming out slowly, then the radiator is toast, no matter how old it is. They can also blow clean fluid through the aux cooler to see if that is the choke point. In any case, they can use the same equipment connected different ways to see where the fluid is being blocked. You need to run these tests and stop messing around with unknowns.
If cash is tight AND the radiator is clogged, then you would stop the hemorage of money if you bypassed the radiator for a few weeks until you could get a new one.
Tranny and radiator = 1 qts in 30 sce (or 0.5 PGM)
Tranny and auc cooler - 3 qts in 30 sec (or 1.5GPM)
I would agree and would have have no prob doing this short term. On a long term basis... I am trying to learn from other on this post.
Yep... good thought on a reverse flow on the radiator... maybe the tranny shop tried this maybe not so I will ask. But the all night run on the radiator did not solve the poor flow.
Agree completely! The radiator is restricting the flow... it got to go.
Yep... they ran the flush cleaner on just the radiator all night. It was no help so the radiator and a big tag on it now... BAD BAD.
I think we have got this nailed with the poor GPM from the radiator. The twists and turns of this post have taken us a bit off course... but the orig question essentially was is 0.5 GPM too slow for the radiator or could there be another problem.
I will get a new radiator... just did not want to through money what could have been the wrong problem.
Since you have narrowed it down to raditor, you could even consider having a raditor shop put a custom high flow oil "tube" in tank if the basic design is flow restrictive. (assuning radiator is in good order otherwise)
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.