10W30 will be a little thicker when it's cold so it will not flow as easily as the 5W30. Both will be the same thickness, or "viscosity" when they are hot. There's little chance you'll notice the difference. 5W30 is typically recommended when the temperature gets real cold or when the manufacturer wants you to use a thinner oil for less friction in the engine and better fuel mileage. That "less friction" does not mean it lubricates better. It means it takes less engine power to push the oil through the passages.
Of more importance is the two-letter designation on the container. All that is necessary is you use oil with the minimum designation it called for when the engine was built. For example, years ago all oil met the designation for "SD" which means "spark ignition" and "D" was better than "C". As the refining process and additives improved significantly to warrant a higher classification, it was listed as "SE", then "SF", etc. You can't find oil with the older classifications any more once the newer ones come out unless you have stuff stored at home. By the way, "CD" means "compression ignition" meaning diesel engines.
My '88 Grand Caravan calls for 10W30 but I've been using 10W40 for the last 148,000 miles because it has less tendency to run out of the engine bearings.
Monday, April 1st, 2013 AT 10:57 PM