Using the wrong oil

what happens if you put 10w 30 oil into a 5w 30 vehicle

Nothing really - at least not right away. If your vehicle calls for 5/30 you should use it, but the world is full of vehicles that ought to have 5/30 but get 10/30 at oil change places. The 10 means that the 10/30 will be a little thicker at start up than 5/30 would be. The oil will take longer to get to some of the places in the engine that need it. But this is most important when the weather is cold - so now that we are getting on to spring (I’m assuming you’re in the northern hemisphere) you’ll be fine with it. And if you live in the south and rarely get freezing level temps your engine will probably never notice the difference.

In short, you should use 5/30, but the 10/30 is no big deal.

Nothing to worry about. IT will be a little slower to start on a cold day and it may reduce fuel mileage, but likely too little to notice.

Don’t worry, but next time use what the manufacturer recommends.

Look in your owner’s manual, most vehicles that state to use 5w30 also give 10w30 as a substitute. If it is very cold where you are at, I would recommend using the 5w30 in the winter time if at all possible.

NOTHING happens. For summer driving, many prefer 10-30 regardless of what the book says. This is NOT a big deal. Much depends on your climate…

I agree with the others with one exception.

If you are driving a Toyota, make sure you use only the recommended 5W30 due to the notoriously high idle during start up.

You’re correct. But let me emphasize that there is cold and there is cold. A few years ago I had occasion to pour three quarts of 10/30 into a car with a leaking rear oil seal on a cheery -18F morning. It looked, and poured, like vasoline. If one lives in Los Angeles or Miami, it probably doesn’t much matter what oil weight goes into the engine. But if one lives in Fairbanks, Fargo, or Saranac Lake, I suspect that even one season of 10 weight oil might materially decrease the lifetime of the engine.