The exact specification will likely be printed in your owner's manual (if you still have it). However, given the age and potential modifications, you'll likely want something a bit more robust. Look for something like:
* 10W-30: This is a common and generally suitable viscosity for older V8s, particularly in warmer climates.
* 10W-40: This is a thicker oil, better suited for higher mileage engines, hotter climates, or heavier loads (like a school bus conversion). This is probably the safer bet.
Crucially, the oil should meet the API (American Petroleum Institute) service classifications:
* SF, SG, SH, SJ, SL, SM or SN: These are older specifications, and finding something explicitly labelled with these older designations might be tough. Modern oils that exceed these levels (like SM or SN) will usually still be suitable. However, check the owner's manual for guidance if possible.
Check your owner's manual! This is the most important source of information. It will provide the specific oil viscosity and API specifications recommended by the manufacturer for your specific engine and year.
Since your van is modified, consider consulting a mechanic specializing in older vehicles or Dodge trucks. They can advise on the best oil for your specific situation and the added stress of the school bus conversion (increased weight and potentially increased operating temperatures).
