The real issue is heat rejection, not just fluid volume. A deep differential cover can add oil and slow the initial temperature rise, but that extra oil also stores heat and takes longer to cool back down. In our loaded hill-climb test, the larger-capacity cover recorded 199 degrees with 7.5 quarts, while the Banks Ram-Air Differential Cover Kit recorded 192.5 degrees with only four quarts. That is the difference between holding heat and shedding it. Our Ram-Air design uses airflow through the cover fins to pull heat out of the lubricant instead of depending on extra oil to mask the problem. If you tow or work your truck hard, airflow is what cools the differential.
Banks conducted a controlled hill-climb comparison on Interstate 5 using a 2018 Chevy Silverado towing an 11,650-pound trailer.
Each run began at the same temperature, with the rear differential brought to operating condition before the climb. The truck then maintained 55 mph up a 6% grade for 5 miles, gaining more than 1,600 feet of elevation.
At the top of the grade, the differential equipped with the stock cover measured 205°F.
The stock cover held 4 quarts of lubricant, establishing the baseline for the towing and climbing conditions.
The same test was repeated with a Mag-Hytec differential cover containing 7.5 quarts of lubricant.
Despite carrying substantially more oil than the stock cover, lubricant temperature at the top of the climb measured 199°F, only 6°F cooler than stock.
Banks then tested its Ram-Air Differential Cover under the same conditions.
With only 4 quarts of lubricant, the same capacity used for the stock-cover test, the Ram-Air recorded a temperature of 192.5°F at the summit.
That made it 12.5°F cooler than stock and 6.5°F cooler than the Mag-Hytec cover.
Under these test conditions, the Banks Ram-Air cover produced roughly twice the temperature reduction of the Mag-Hytec cover compared with stock.
The Mag-Hytec reduced temperature by 6°F, while the Ram-Air reduced it by 12.5°F despite using 3.5 fewer quarts of lubricant.
The comparison demonstrates that greater lubricant capacity alone did not produce the lowest differential temperature.
In this test, the 7.5-quart Mag-Hytec ran hotter than the 4-quart Banks Ram-Air. The results support Banks' conclusion that cover design and airflow can have a greater effect on differential cooling than simply increasing oil volume.
