A few months ago I installed 4.7 gears in my t-case. The gears are a bit noisier than stock, but are not noticeable with the radio on. Problem now is that my radio got stolen.

The noise from the gears isn't terrible, but I was wondering if it'd be a good idea to quiet them down by using thicker oil. The Trail Gear website calls for 80-90 oil with the 4.7 gears. Anyone see any problems with something like 80-140? Btw, summer temps here are in the low 100s, and winter lows are in the 40s.

 

You might get slightly worse gas mileage; MAYBE you'll feel a slight drag on power compared to the 80-90. I had 75-140 in my rear diff for awhile(instead of 75-90) and I could tell...it seemed like the engine lost a tiny amount(maybe 3%?) of its power. I could have lived with it.