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NP231 Black Fluid.....

I'd actually consider putting a gauge in instead of a warning lamp. That way you can get an idea for what temps it rides at under what conditions and tell if something seems out of whack. Maybe a second trans temp sensor with a switch to select which you're looking at?

I know my bone stock NP231 behind a stock 4.0/AX15 will get hot enough to give mild second degree burns to the back of my hand while prying the shift lever away from it (I didn't have a linkage hooked up...) but I'm not sure what temp to expect normally.
 
Dont mean to keep reviving this post but I want to close it out. I rebuilt the 231. Added a temp sensor and I am using a toggle switch at my trans temp gauge so i can toggle between transmission temp and transfer case temp. Also I added 2 liters of synthetic ATF when it was on the bench (instead of the 1.5 i normally can get in there).


Been driving it a bit in the 95 degree heat. Transmission stays at its normal 150 and gets up to 170 occasionally while pulling a grade. Transfer case lives at 150-170 as well but will get up to 210 after 70mph going uphill. Takes awhile to cool off too. I Didnt realize they got that hot in 2wd. Maybe its from all the heat of the V8 getting forced through the tunnel and blasted onto the t-case. Anyway, now we know what they run at, 210....which is a bit north of where I want it. Doing a 800 mile trip here shortly (in two weeks) towing the trailer, well see what it gets up to then....


IMG_6650.jpg
 
t-case also has no cooler to drop it's temp like the trans does......and no thin pan in the airflow to help either

This.

I have always wondered about the ability to add a cooler. I think the easiest approach would be to attach a heatsink to the bottom- but that brings issues with impact and the like.

Very likely, the best answer is to run a high quality synthetic and not worry about it.
 
Has anybody tried Royal Purple Synchromax synthetic manual transmission fluid ? they say it's made to replace auto trans fluid in manual trans and transfer cases .I using it in my cars 5 speed and it does work good , it shifts better and is quieter .
 
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