How much oil do I put in a Briggs and Straton Bolens push lawn mower?
Model 11A-084E765 4.5hp
Verify- the best type of oil is straight 30 weight, right?

Yes, SAE 30 is the correct weight.
Capacity? I'm not sure but if you have two quarts available, that should be more than enough. Just add slowly and check the level periodically. Start the engine first, then recheck for correct oil level.

The correct oil capacity USED to be 20 oz. then briggs came out with the same bottle just a little smaller and made it only 18oz. So do as capt. Rich suggested and recheck the level. But if the crankcase is drained completely, it will take the small briggs and stratton bottle that contains either 20 or 18ozs. The variance depends on how long the dealer has had the oil in stock. And sae 30 is the correct viscosity of oil. I would only use oem briggs and stratton oil.

My instruction manual for that particular mower says it should have
18 ounces to re-fill after a change.

Also you can run 5w30 SYNTHETIC motor oil in it as first preference.
Only use 30 weight if you are not going to run it below 40 degrees F.

Hi,
Think you got that backwards, 30W above 40 degrees.
Peace,
Clarke