this may be a dumb question, but i am a newb so sorry. But which port on the the tranny is for the feed and which is the return. and I have a flexalite 20,000 GVW cooler, size is 20" by 8", would i be better off going through the radiator then to the cooler, or take the radiator out all together? thanks

 

If you have a 97 and newer 4L80E, the fitting on the front of the trans case is the pressure line to the cooler, and the fitting on the rear of the case is the return line from the cooler.

As for whether or not to use the radiator's trans cooler, there's a lot of debate. I took my 4L80E out of a cargo van, and it did not have a cooler going through the radiator (only a separate independent cooler) so I did not run mine through the radiator. However, I did put a Derale fluid thermostat in line with my cooler. It cycles the fluid through the cooler at 180 degrees.

 

It's usually OK to just use an external cooler. My climate ranges from slightly below freezing maybe a total of a week out of the year, up to 100 in the summer. I don't think I'm ever in danger of having the fluid too cold, so in my case I skip the thermostat for the trans fluid. If you've ever had the radiator cooler break, giving you Pepto Bismol coolant and a (eventually) ruined trans, it's not worth the headache. I guess the OEMs do it to keep the trans temp normalized for just about any climate. I don't know.

 

Front line on a late model unit 97 and up. Top line on a 96 and earlier.

 

thanks for the responses! My next question is how much fluid will it take to fill it up from empty?