Outdoor Power Equipment and Small Engines - Oil?

Hi,
This is my first post, so go easy please.

Between myself and a friend we have a fair number of small four stroke engines on various implements.

2 X B+S 3.5 hp
1 X B+S 11.5 hp
1 X B+S 5.5 hp
1 X B+S 10 hp
2 X Honda 160cc

Is there any reason why I shouldn't use normal 10w40 oil (car type) in them? I hear people advise against it, but no one can ever tell me why.

Use 10W30. No one is using 10W40 anymore. 10W30 has different and better lubricating properties than 10W40. And since it is a little thinner, engine maufacturers have found that the oil goes thry the engine faster on cold starts resulting in less wear.

A 10w30 and a 10w40 are the same thickness at startup its at operating temperature that the 10w30 is thinner. The oil that is used should depend upon the outside temperature that the engine is operating in. I think most 4 cycle engines used in warm temps. call for straight 30w above 45-50 degree weather. The problem with multi-vis oils such as 5w30 & 10w30 etc. evaporate much quicker than straight weight oils but allow for easier starting.

07bloomfieldb,
Welcome to the forum, you must have a mean streak to have posted this, lol. IMHO, 30w above 40degrees 10W30 below 40degrees, if it runs above 4000 rpm or below 1500 for extended periods of time check the manufacturers specs. Have a good one. Geo

Seeing that you are in the UK, the above temps are in Farenheit. If it's above 40 degrees C in England, stay inside and enjoy a frosty cold adult beverege.:D:D