Short answer: Viscosity measures how easily oil flows. In a grade such as 5W-30, the number before the W shows how the oil performs on a cold start and the number after shows its thickness at normal operating temperature. The right viscosity is the one the vehicle manufacturer specifies in the owner's manual or on the oil cap.
How to read the label
- The viscosity grade (for example 0W-20, 5W-30, 15W-40): the first figure is cold start, the second is thickness at operating temperature.
- The API classification: S for gasoline engines and C for diesel engines; later letters in the alphabet indicate newer standards.
- The type: conventional, synthetic blend or full synthetic. Alternating between synthetic and conventional will not damage a healthy engine.
What to stock
It depends on the cars that come into your shop. Review your work orders from the last few months and see which grades repeat: those go in drums or bulk, and the less frequent ones in quarts. Diesel truck and fleet engines usually run heavier grades and C-rated oil.
We can help build the list
If you are not sure which grades to stock, your ADB rep can help you build a list based on the vehicles you service, and quote it line by line.
Frequently asked questions
What does the W in 5W-30 mean?
It refers to cold (winter) performance. The number before the W shows how the oil starts in the cold; the number after, its thickness at operating temperature.
Can I switch from conventional to synthetic?
Yes. Alternating between full synthetic and conventional will not damage a healthy engine.
What does the API classification mean?
It is a two-letter code: S for gasoline engines and C for diesel. Later letters indicate newer standards.
How do I know which viscosity a vehicle takes?
The manufacturer lists it in the owner's manual, and often on the oil cap.
About ADB Automotive
ADB Automotive, Inc. is a family-owned wholesale distributor in the Miami area, founded in 2002 by Francisco and Bryan Almaguer, backed by more than 40 years of the family in the automotive industry. It sells to businesses only and delivers daily across Miami-Dade, Broward and Palm Beach.
Address: 2175 E 11th Ave, Hialeah, FL 33013 · Phone: 305-836-4222 · WhatsApp: 305-984-3434 · Email: sales@adbauto.com · Monday to Friday, 8 AM to 5 PM.