time for Ensure?

I've got 114,449 miles on the clock and I'm past due for an oil change.

Is it time for my car to stop drinking soda (5W-30) and start drinking ensure (10W-30)?

No, but you may want to go to a 5W40 or 10W40 weight oil.

whats the diff btwn 10W-40 and 10W-30?

Both numbers are a measure of flow (viscosity) at specific temperatures, against a standard straight weight oil. The first number is the cold flow rate, the second is the hot flow rate.
So, a 10W30 and a 10W40 both flow at the same rate as a straight 10 weight oil would when it's cold. And flow like a 30 weight and a 40 weight oil when they're hot.
So the 30 is "thinner" or less viscous then the 40 when it's hot. Because it's thinner it would appear to give less protection in the engine when it's hot or over heating. So one might assume that a higher weight would be better, like a 20W50.
Unfortunately nothing is that simple. Higher weight oils take more HP to pump though the engine and have more internal friction (cause heating). In the old days most drag racer ran 20W50 in there cars at the track, because most engines were machined with larger clearences on the mains and rods, they were run very hard and often near over heating, so they wanted the most protection they could get and were willing to sacrifice a little HP to get it.
Modern engine are machined with smaller clearences and run hotter then ever before. And the trend has been to use higher quality (synthetic oil) with low overall viscosities to reduce friction and Hp loss. This helps with the gas mileage figures.
The manufacturers recommended oil weights (from the owners manual) are probably good for 95% of all driving and drivers.
Of course us Hot Rodders always want more/better, and tend to run slightly high or wider viscosity oils. This is of course just the tip of the iceburg, there is much much more to this subject and to correct oil selection.
Bottom line on all this is, that in your case with your engine miles, you could go with a slightly high viscosity oil like a 10W40 or 5W40.

I got a full synthetic 10W-30. In 3,000 i'll try 10W-40. Thanks for the info, very informative.