Am I at risk of blowing the engine on my Riding Lawnmower?

You can use a synthetic oil. However, we do not recommend a 10W-40. Please use a 5W-30 synthetic oil. You can find additional information on the Briggs & Stratton oil recommendations at the link below.

http://www.briggsandstratton.com/us/en/support/faq...

your best bet is whatever the manufacturer recommends.. Briggs sells a SAE 30 for this mower type.. The oil you added will be fine. a 10w-40 is a thicker oil so it would coat the parts better but not a huge difference if over time say a few years from now it smokes a bit then maybe up the viscosity a bit..

You are not at risk of blowing your engine by using 10w-30,however it is best to follow the manufactures recommendations if it's under warranty

Used it for years in mine then switched to 5w-30 when that is what my sons car needed. Never had an issue. In the states, unless your running it in cold weather, al you really need is 30 like James stated, that is the manufactures recommendation.

here in the uk we are more experienced than america when it comes to synthetic oils ..you are at no risk to harming your engine ...the oil will run thinner in hot weather ..but being fully synthetic it can handle that easily ...i use the same oil in my murray tractor ..thats a briggs and stratton engine ..and as its in the south of france the tempureture gets to 50c ..no probs

Your only danger is if you overfill the oil, then you can blow seals. Oil on its own is all good. It's a lawn tractor, not NASCAR.