I have a 1990 cherokee with an ax-15 and 31s when I go down the interstate at about 75mph and 2 1/4 rpm my temp starts climbing slowly if i put lower gears in it would it help or do i need a heavy duty radiator

 

you shouldnt need to regear with 31s

 

i have the same set up you do (31s ax15) and you definitely shouldn't have a problem with gears even though they are only 3.07s, 2,250 rpm sounds just right at 75mph, but the thing is your jeep should be able to turn 2,250 all day no problem, if it was 3k rpm that would be a different story...i would check your cooling system, is the overflow tank at the right level?, is your t-stat opening and closing? (try turning the heat on to see if it makes the temp go down) and does the temp keep climbing until the engine starts overheating? or does it stop?, my jeep goes a little bit above 210 all the time but always works its way back down.

 

i agree your problem is not gear related

 

i have the same setup as both of you and my engine sits at about 210 and as for rpms i think i sit just above 2 at 75 but im not to sure.. i rarerly go over 68-70ish.. if you want to regear just get a set of axles with 3.55s or 3.73s from an auto.. both axles shouldnt cost you that much unless your shooting for a d44..

 

you might want to look at the fan clutch

 

x2

 

The temp just goes up very slowly and won't be over heated until a good hour of 75+ speed the fan functions properly thermostat is good and the overflow tank is filled properly