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Automatic Transmission Fluid temperature range


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6 replies to this topic

#1 WhiteJZX100

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Posted 02 March 2006 - 09:52 AM

Hey guys,

Just wondering what the optimal operating temperature for the automatic transmission fluid in the auto boxes we have is? I think we use Dexron III grade stuff, but i havent been able to find what the Dexron III specs are.

Also, how would you go about fitting a thermostat to a transmission cooler to maintain an optimal operating temperature? Would this also work for a oil cooler?

I'm looking at purchasing a transmission cooler (or two, cheers ghost!) and a oil cooler kit and want to fit thermostats to both of them. Anyone done this?

Thanks!
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#2 markII streeter

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Posted 02 March 2006 - 10:13 AM

Would this also work for a oil cooler?


Most oil coolers come with either a relocation plate or a sandwitch plate which has provisioning for 2 senders (the oil temp and oil pressure senders). As for transmision cooler it shouldn't be too hard to adapt a sender to fit into one of the hoses. I had a omori water temp sender that sat in the middle of two sections of hose, I assume you could do a similar thing with the auto trans cooler.
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#3 WhiteJZX100

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Posted 02 March 2006 - 10:16 AM

Most oil coolers come with either a relocation plate or a sandwitch plate which has provisioning for 2 senders (the oil temp and oil pressure senders). As for transmision cooler it shouldn't be too hard to adapt a sender to fit into one of the hoses. I had a omori water temp sender that sat in the middle of two sections of hose, I assume you could do a similar thing with the auto trans cooler.


Yup, i was planning on mounting a Temp sensor and Pressure sensor on the relocation plate, but what i was after was a thermostat to control the flow of oil to the cooler. Make it work similarly to the coolant system in place for the engine, with the thermostat closed until the coolant reaches a specified temerature. This will mean that it wont take forever for the oil to get up to operating temperature and only get cooled when required.
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#4 ghost

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Posted 02 March 2006 - 01:19 PM

Decent oil cooler kits have a tremostat built in. If it is a sandwich plate, then it should be in that. If it is a filter relocater kit as well then the thermostat should be in the remote plate where the filter sits.

This way the oil always passes through the filter regardless of the temperature.
My Greddy kit has the thermostat in the sandwich plate housing.

Stadard autos run trans fluid through the bottom part of the radiator and don't need a thermostat because the water cooling system regulates things to some degree. When adding additional coolers your transmission fluid will definitely run cooler and be less regulated I suppose, but the torque converter is producing a fair bit of heat just idling so I dont think it will get too cool (is there such a thing in cars)

Ok obviously you want you car to warm up as quick as possible and it would be bad to drive hard on cold oil, hence thermostats in water and oil systems, but I don't think one is necessary for auto trans.
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#5 WhiteJZX100

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Posted 02 March 2006 - 01:46 PM

Decent oil cooler kits have a tremostat built in. If it is a sandwich plate, then it should be in that. If it is a filter relocater kit as well then the thermostat should be in the remote plate where the filter sits.

This way the oil always passes through the filter regardless of the temperature.
My Greddy kit has the thermostat in the sandwich plate housing.

Stadard autos run trans fluid through the bottom part of the radiator and don't need a thermostat because the water cooling system regulates things to some degree. When adding additional coolers your transmission fluid will definitely run cooler and be less regulated I suppose, but the torque converter is producing a fair bit of heat just idling so I dont think it will get too cool (is there such a thing in cars)

Ok obviously you want you car to warm up as quick as possible and it would be bad to drive hard on cold oil, hence thermostats in water and oil systems, but I don't think one is necessary for auto trans.



Any idea on the safe operating temperature for the auto transmission fluid? I'm seeing 70 degrees + on my PFC handcontroller, and i've got no baseline to go by...

Oh and Ghost, do you bypass the stock radiator cooler with your setup and go straight to the additional coolers or do you run it thru the stock cooler then thru the additional ones?

Edited by WhiteJZX100, 02 March 2006 - 01:47 PM.

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#6 ghost

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Posted 02 March 2006 - 02:14 PM

Any idea on the safe operating temperature for the auto transmission fluid? I'm seeing 70 degrees + on my PFC handcontroller, and i've got no baseline to go by...

Oh and Ghost, do you bypass the stock radiator cooler with your setup and go straight to the additional coolers or do you run it thru the stock cooler then thru the additional ones?


I have no idea on the temps as I have no gauge.
My coolers are connected gearbox-radiator-cooler-cooler-gearbox.
So I have still utilised the rad cooling. Probably more flow restriction compared to having one big cooler but I dont think it really matters.
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#7 Arthur

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Posted 20 April 2006 - 11:22 PM

I have no idea on the temps as I have no gauge.
My coolers are connected gearbox-radiator-cooler-cooler-gearbox.
So I have still utilised the rad cooling. Probably more flow restriction compared to having one big cooler but I dont think it really matters.


The question asked by the previous post concerned a base line for transmission temps to know whether a 70c operating temp is ok.
I have info from a reliable authority that Ford [wash my mouth out] had a thermostat in some transmissions of the 90's set at about 80c to maintain detergent wash properties and satisfactory servo piston/clutch pack operation. Magnesium was usually the detergent additive.

Unlike engine oils auto transmission fluid is designed for its hydraulic properties with friction modifiers added to suit the various transmission types. Dextron 3 is the recommended fluid in our auto boxes that is matched to the clutch pack material and gives smooth changes over a wide range of conditions.

Fitting an external cooler is added insurance for track use, towing or any other sustained punishment and should be fitted after the radiator cooler. The main reason for this configuration is that the fluid needs to attain an operating temp of about 70c which is preheated and regulated to a large extent by the temp of the radiator coolant. It needs temperature to operate efficiently. If its hotter than the radiator coolant it looses heat and vice versa.

A problem can arise though, with sustained punishment, of heat soak in the transmission resulting in raised temps that an external cooler may not control. A possible fix for this is a switch to a synthetic Dextron 3 which in Castrol form is Transmax Z. This is good for another 25c above the standard spec.
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