The viscosity ratings have to be the same regardless of what the oil is made from. Those numbers refer to how fluid the oil is at different temperatures. The "30" means the oil will flow less easily in warm weather during a cold-engine start-up. The thinner oil is more likely to squirt from the tiny holes in the connecting rods, onto the cylinder walls, to lubricate the pistons. While this might not be a big issue, less piston scuffing will occur if you can get oil onto the cylinder walls as soon as possible after start-up.
The disadvantage to using synthetic oil is the higher cost, and if there is a small, insignificant leak, it will leak out much faster. In my opinion, there is no advantage to using it, but opinions vary. It is supposed to make really cold engines easier to start, but since my first fuel-injected '88 Grand Caravan, I've never had a failure to start in the middle of Wisconsin winters, except when the batteries decided to give up.
My biggest concern with synthetic oil is they almost always advertise the much longer oil change intervals to offset the higher cost. The problem is oil is oil, and will always be oil. It's the additives that wear out over time, and the contaminants that build up in it, that are the reason for the recommended intervals. Most additives, including seal conditioners, anti-foaming agents, dispersants, and detergents, wear out in about 3,000 miles. The dispersants carry the contaminants to the oil filter. Using synthetic oil doesn't give the filter more room to hold the stuff we want to remove. If the filter becomes plugged, there is always a bypass valve around it. The engineers feel unfiltered oil going to the engine is better than no oil. That is definitely true, but cleaned oil is better than oil with carbon and metal particles in it.
Wednesday, April 12th, 2017 AT 5:19 PM