Since your co-worker finds fair amounts of both grades (10W-30 and 15W-40) in store ... I assumed we were talking about the final product. You are also talking about Wal-Mart, ST and prices which relates to the final product.
For example Super Tech has the following 10W-30:
- Conventional
- Full Synthetic
- Advanced Full Synthetic
- All Mile Coverage Synthetic Blend
- High Mileage Full Synthetic
These are rated from 5000 miles to 20,000 miles. Marketing aside, they all must pass some approvals and performance levels.
On the back of the jug, they have ratings for the following categories:
- Reduces Engine Wear
- Combats Sludge and Deposits
- Extreme Temperature Protection
Then we have many other 10W-30s like M1 EP, Ravenol, Amsoil SS, etc. not all created equally.
These were some other 10W-30s I had considered in the past and finally settled on M1 EP 10W-30 because it has my approval.
