2004 Chevy 2500HD 4 doors
 

Hello, just brought a 2004 Chevy 2500HD 4x4 with 200,000 miles to plow snow at Amazon in Denver Colorado. Will want to change all the fluid and this truck will be for work as snowplow only. Have some question to ask.
1. engine oil, it recommended to use 5w-30 but since it a high mileage, should i use 10w-30 instead?
2. front and rear differential. Should i use 75w-90 or 75w-140
3. What do you think about using product as moly engine flush.

Thank you

1.if the oil pressure is ok...use the recommended oil. synthetic is best for cold weather start up...less wear and easier on the battery to crank. 5/30 is better for cold weather
2use the oem recommend diff fluid
3never tried it.

Agree w/ TECH2. use 75w90 in both axles and dextron atf in the transfer case unless you have auto 4wd it uses autotrak II