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175-200°F measured at the pan is pretty much ideal.

Max allowable for short durations should be around 275°F at the pan (300°F entering the trans cooler).

And it never hurts to have some insurance: Grab a bottle of the appropriate Lube Gard (Napa BK 765-2601 is the one for Dexron, there are others) and put it in. I've seen that stuff make a HUGE difference in the lifespan of transmissions that see extreme severe duty use (police academy training cars..)
 

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For the most part I agree with machman 175-200 is fine for regular non-synthetic ATF. I have no experience with Lubeguard, and I don't use any other additives to comment on. I do use Schaeffers trans fluid which is a semi synthetic, it is a very good quality ATF. The 275-300 degree max is a little high IMO particularly for regular ATF. There is synthetic ATF that is good to 400 but it is very pricey.
Another rule of thumb I was taught is 100* above ambient air temps is a god indicator for adequate trans fluid cooling.
 

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175-200°F measured at the pan is pretty much ideal.

Max allowable for short durations should be around 275°F at the pan (300°F entering the trans cooler).
I too have to agree. Here is some info about tranny coolers and it talks about tranny temp and ideal operating range.

If you examine the location and orientation of the heat exchanger in the radiator, you will see that it is located where the radiator's bypass water flow runs. Normally, the heater core is fed from an engine tap before the coolant thermostat, so that it sees warm water as soon as any significant heat has been produced by the engine warming up. The return water from the heater core is dumped back into the radiator in a place where it will flow across the heat exchanger before it re-enters the water pump and makes another circuit. This means that the heater core water, which warms up more quickly than the main radiator water, also serves to warm up the transmission fluid in the heat exchanger. This is important because warm transmission fluid is only a so-so lubricant, and cold transmission fluid is even worse. You want to get the fuid warmed up as soon as possible in order to lengthen the life and improve the durability of the transmission. The waste water from the heater core flowing over the heat exchanger does this.

The heat exchanger also cools the transmission during normal operation. When the fluid is hotter than the radiator coolant then the fluid loses heat to the coolant, and the cooler fluid is returned to the transmission. The net effect is that the temperature of the fluid from the heat exchanger is loosely regulated to about 200 degrees Fahrenheit, and this warm fluid is used to bathe the working parts of the transmission.

There are several things that can be deduced from the above:

You want the radiator heat exchanger to be the last thing in the hydraulic circuit before the fluid is returned to the transmission. If you add an external fluid cooler (a really good idea), place it before the heat exchanger so that the radiator heat exchanger has the "last word".

Keep the restriction in any cooler low. Since a high volume of oil flows in this circuit at times, you need low restriction to avoid having pressure build up in the torque converter. That pressure buildup is bad for a lot of things, including the engine's thrust bearing, the torque converter, and the various bearings and washers in the transmission which handle the axial thrust load. In a really bad case, excess converter pressure can crack a transmission case.

Do not block the hydraulic lines in any manner. This includes thermostats and shutoff valves. Blocking the fluid flow not only results in very high converter and line pressures, it also causes a lack of lubrication inside the transmission which will quickly lead to transmission failure.

Keep the heater coolant flow through the radiator intact. If you wish to remove the heater, then use a piece of hose instead of the heater core, but let the coolant circulate around the heat exchanger in the radiator.

Keep the inside of the cooling system in good shape. This maintains the effectiveness of the heat exchanger, and greatly reduces the likelihood of the heat exchanger corroding through. BTW, if engine coolant gets into the transmission then you will have to replace all of the friction materials in the transmission as they are made of paper and will disintegrate when wet.


Here's where I got it http://www.442.com/oldsfaq/oftrn.htm

I don't neccessarily agree on where the info suggests putting the tranny cooler but running a tranny in the right temp range will give it the most life. I've seen my gauge slowly climb to 250F for a short duration and that had me pretty nervous. I did pull over and let if cool down. If I'm towing something 220-230F is my warning to watch it closely and if it keeps climbing it's time to let it cool off. My $.02
 

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I have had mine as high as 250* once. I had the idle set high and after I turn the idle back down it hasn't goten as hot. I have an air to oil cooler. Running down the road not towing anything it usually is about 150-165 coming out of the trans. When I am in town with a lot of stop and go it get a little above 180. So form what I read that should be okay right?

Thankyou for you help.
 

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http://www.txchange.com/heatchrt.htm

I have seen this heat/tranmission failure chart elsewhere too, it is just for reference here, I have not done business with this company and know nothing of them.

With the exception of synthetics, transmission fluid is mineral oil with various additive packages. Each manufacturer specifies their own package. That being said, it does not take much heat to cook down the fluid, that is why it is very important to have a gauge on the cooler out line, the hottest fluid can be gauged right there.
 
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