Z32 Turning a oil cooler into a trans cooler would it be ok.

Discussion in 'Technical' started by ADAMZX, Feb 23, 2022.


    ADAMZX 2000spec Conversion

    Hey everyone, so im in full hardware mode as I like to call it, planning all of the things I want to do with my Z during the rebuild phase and one idea I've been toying with for years now is to install one of those OEM TT euro style oil cooler's into the factory mounting location on the cross member and use it as an external transmission cooler for my factory 4 speed auto i'm currently running.

    I know there are a ton of variables to consider with this idea which is why I havent mentioned it before on the forums, as I've been researching and checking the viablilty of this idea on the net before I proceed any futher for a long time now and I was kinda planning to make this all a surprise video idea/content for the channel but there are still alot of unknowns I have yet to find answers for with this idea and I just thought Id ask the question and hopefully get those answers to my questions from the more mechanically minded people on here about what they thought of the idea and whether its possible or not and whether its ok to do or not.

    What i'm not sure about is is that oil cooler way to big to be a trans cooler and would the transmission fluid run too cool for everyday driving. Currently Im using the standard setup with the inbuilt trans cooler in the radiator which works perflect fine so far but if this idea was possible i could then install the new trans cooler in the same location as the TT has for the oil cooler and just route the hoses to the transmission with some modification oblivously and that make the whole setup all look factory spec and I would never need to worry about if the ATF fluid was getting too hot and cause the transmission to fail in the future.

    But if the fluid runs to cool it might also have a negative effect on the transmission in another way, so thats why im here to ask the big question and hopefully get an answer I have yet to find some far.
  2. ryzan

    ryzan Black Mesa? Fat chance...

    It would be fine, however I'd run it in parallel with the factory cooler. The factory cooler doesn't just help maintain trans temps, but also helps to get the trans oil up to temp quicker too. Your external cooler would help remove temperature before then going through the radiator.
    MickW and ADAMZX like this.
  3. The Aussie Shed

    The Aussie Shed New Member

    G'day Adam, kinda depends really. Are Trans Temps an issue for you? Apologies, I have no idea how much power you are pushing through it.
    Unless you live in Siberia you wont have issues with the Trans being "To Cool".
    I run a 25 Row Setrab Oil Cooler on the Transmission in my 370gt, yes its an Re5 but they are very similar Transmissions.
    Over the years I did a lot of Temp testing with my setup in various stages of its creation, firstly, I added a secondary temperature sensor to the trans, as the factory sensor data is only available through obd2 & I dont have obd2 compatible gauges.
    With my setup, as far as Temps go, I monitor Coolant temp, Engine Oil Temp, Trans Temp & Diff oil Temp. (Data is King)
    Initially I added a 19 row Setrab & disconnected the Radiator Trans Cooler. At this Stage the car was still NA.
    Trans warm up times were almost identical & cooling was very much improved when loading it up.
    The biggest benefit was the Engine Cooling System heat up & recovery times were drastically improved, due to the reduced thermal load.
    Post Turbo Build, I now run a Dual Pass CSF Radiator (not available for Auto's) & a Bigger 25 Row Setrab Oil Cooler on the trans, again, warm up is not an issue.
    The Car now makes close to 400rwkw & I can lean on it really hard on hot days out without any dramas.
    A different vehicle yes, but the same principles still apply.
    Get the Data.
    Make Improvements where the Data tells you.
    Dont waste your money doing things you don't need to do.
    Add more Power.
    Rinse & Repeat.
    Cheers Mate.
    MickW and ADAMZX like this.

    ADAMZX 2000spec Conversion

    Hey aussie shed, thanks for your detailed replay to my questions regarding this setup. Your response has given me alot of solid answers I was looking for which I appreciate very much.

    Well I cant know for sure, as I have no way to monitor trans fluid temps from my transmission ECU even with conzult's sensor readout. All I can tell you is the temp sensor is reading 1.48 volts at idle. Otherwise the transmission I've been running is working flawlessly and shifts perfectly. And as for power, I'm running a stock na with nearly 290,000 km connected to a transmission from a 96 ADM model with low kms I believe. I have no plans to increase my Z's power levels at all and I'm more interested in longevity more then power.

    Perfect, I have seen the same answers on other forums about temps not changing, so I'm happy to know that wont change all

    Having watched your youtube videos as your Z build progress's, I can tell you know your stuff when it comes to modifications and performance upgrades. Your very much like my dad when it comes to thinking outside the box and finding solutions to problems when you come accross them and the only difference between you and my dad is, my dad doesnt like upgrading a car to be more powerful which is probably why I sometimes argue with him regarding these types of ideas and plans for mods with my Z which he flat out disproves of.

    Anyways this setup is more a show thing with a hope for increased realiability for the transmission long term. My Z has been through 2 transmissions so far in its lifetime, with the first original transmission going out on me in 2007 literally 15 months into my first full year of ownership. That transmission was replaced with an unknown km's wreckers tranmission that lasted the next 10 years before that one just went out on me as well but there is a whole 10 years of electrical gremlins with that transmission to go into but lets just say that transmission went out on me a month after I serviced it myself, after 10 years of doing nothing and the fluid that came out of the pan was black as tar. Luckily for me the current transmission I'm running came out of a 96 ADM model that a member in NSW (i think) was stripping and once I replaced the ATCU module to fix a intermiate shifting issue i was experiencing, this transmission as been the best transmission I've had to date.

    So you can see I'm always worried about when or if this transmission will go on me and though I have vowed to maintain a regualr 40k service of the fluid and filter on this transmission, I know its common practice for transmissions shops to install a external trans cooler to provide better cooling for the trans and I figured this setup would give me the best of everything and look stock. So with all this information now, I am going to push ahead with the conversion to the new cooler setup, but I just need a couple more parts to make it a reality and one of those parts which I have yet to find is a TT style power steering hose line that runs along the front of cross member which the na line sits ontop of the panel and prevents the mounting plate from being installed, once I have that part the next problem is how do I connect the two different hose sizes together as I know that the trans cooler hoses off of the tranmission lines are 8mm in diameter but I think the oil cooler barbs are at least 10 or maybe 12mm in diameter and though I could simply put a reducing barb fitting in the hose system to connect everything up, wouldnt that not cause problems with the fluid flowing from a smaller hose to a bigger hose and then from a bigger hose to a smaller hose.

    My questions to answer.
    The Aussie Shed likes this.
  5. MickW

    MickW Carntry member...

    To run a series / parallel switchover setup for the ATF you'd need one of these oil thermostats -


    You'd configure it so the ATF gets heated up as quick as possible via the radiator.
    Then as the ATF starts to get hotter it will be sent to the external cooler.

    ** The above setup is not configured for that.
  6. MickW

    MickW Carntry member...

    I learned the hard way how important that is after re-routing the ATF away from the OEM auto radiator to an independant ATF cooler system. Problem is, the temperature sensor in the autos' sump won't let you have overdrive or lockup until the ATF temperature gets high enough and the shifts are harsher than they should be while the tranny is cold. Not so bad for our Aussie climate range but I often wonder how they get on in the sub-zero temps in other countries.
  7. MickW

    MickW Carntry member...

    Well summed up mate! The tldr; version is, be careful about messing with delicate balances.

    I was halfway through writing a similar response to maybe fit some gauges to the transmission to gather data. Such as line pressure and temperature gauges like these -


    But that's getting into custom work, gets exy if you can't DIY. And probably unnecessary for Adam.

    A permanent ATF temperature gauge? Maybe not needed in this case. But...

    A quick temporary DIY gauge for the ATF temp can be done with a multimeter that has a temp setting and a K type thermocouple long enough to reach into the ATF sump via the dipstick hole. I've lost the pics of that but it's self-explanatory. ATF won't come exploding out the dipstick hole but it doesn't hurt to put a bit of cloth around the sensor wire at the top. And the temp sensor won't get drawn in and crunched up by gears or do any damage if you insert it to the same depth as the ATF dipstick. Promise :)

    It was ghetto but it worked well enough to tell me that yes, the factory temp sensor was working accurately.
    If your temps are accurate but always too high and you're having repeated tranny failures?
    Check the lockup clutch is working. Someone please fact check me on this -

    As I understand it, whenever your revs are below 2,500 ( stock torque converter ) you're generating heat in the trannny. But when it locks up you're no longer using pumped ATF for motion and not generating near as much heat. Is that about right?

    If the Lockup clutch is OK then maybe fit some extra ATF cooling. Then you might need a line pressure gauge as well when you start running extra hoses to remote coolers, in case one of the hoses fails later on. The gauge would need an audible alarm to be any use though. As in, if the alarm squeals you need to pull over immediately.

    Hope that all made sense, I do tend to ramble a bit :)
  8. MickW

    MickW Carntry member...

    Hi Adam. I've been leap-frogging through your thread and answering other members, sorry.
    Hopefully you'll find some useful snippets amongst what I've already posted.

    Also, I've restored the pics in my 2011 post about messing around with my TT auto tranny.
    Try not to cringe at my commentary style.


    ADAMZX 2000spec Conversion

    No thats fine Mick, information is key here and you've answered then all very well and I do appreciate your responses to all the questions in this thread. Atm this idea is currently a pipe dream for now as I still need to collect a few more cruical parts to make it happen like the power steering return hose line I mentioned early which I am hopefully to secure in the next few weeks and once I do I can then go full steam ahead to make this new setup a practical and functional one.

    Ah yes your tranny thread which I must thank you massively for, as if it wasnt for your information about the repair of the Auto ECU i wouldnt have finally solved my intermediate shifting problem I had been experiencing with my second and third transmissions that lasted for nearly 10 years. After reading your solution about getting the ecu board repaired by injectronics, I sourced a second hand replacement auto ecu which when installed resulted in my shifting issues disapearing overnight and I have had nothing but smooth and crisp shifting every since then as well as going from having several error codes coming up to now only having one which is a T/C value solenoid fault which I plan to replace when I service the transmissions fluid and filter during this rebuild phase.
    MickW likes this.

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