The best is what the owners manual calls for. The numbers you mention
are nonsense numbers.

Usually Jeeps use 10W30 for normal North American temperatures.

'My' XJ's owners manual calls for 20W40 or 20W50 for temperatures 'only'
above freezing or 30F or -1C up to as hot as it gets.

For temperatures above 0F or -18C it calls for 10W30 or 10W40 up to as
hot as it gets.

For temperatures 'only' Below 60F or 16C it calls for 5W30 down to as
low as it gets.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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gcdenis wrote:
>
> whats the difference between 5w20-40 and 10w20-40. whens it best to use one
> or the other? Whats best for my '96 cherokee?