If this has been thrashed about I couldn't find it but I NEED a trans cooler, (https://www.cherokeeforum.com/f2/bil...railer-252685/) Narrowed it down to the Hayden 677 or 678.

The Hayden site lists the 677 as the right part for the '99 4.0L and even a YouTuber thought the 678 he was installing might be too much. Any other ideas or suggestions?

 

I did the 677, it may have been the summit brand equivalent, but it works good, on 100 degree days the temp never gets above 180, usually hovers around 170 or so.

 

They are universal coolers so most sites won't list them as a direct fit for your Jeep. When it comes to transmission coolers the bigger the better, I have a Haden 405 on mine and it works great, but it's a tube and fin cooler which isn't as efficient as a stacked plate cooler like the 678.

 

Here's a good read on coolers:
https://transmissioncoolerguide.com/...ission-cooler/