Small Engines (Lawn Mowers, etc.): Oil, shell helix, recommended oil

Question
Hi Michael, I am just wondering if you can use Shell Helix Ultra 5W-40 grade automotive engine oil in small engines. I know that the recommended oil is 30W but will the viscosity & density differnece harm any of the components?

If you could get back to me it would be appreciated.
Thanks,
Jay.

Answer
Hi Jay,

Sorry, I am not familiar with the Ultra 5W-40.  As you mention, usually a straight 30W is recommended.  Now, that is for temps over 40 degrees F.  A 10W-40 is not okay because it is really a 10 weight.  If I had to guess, I would say the 5W-40 would not be good for an air cooled small engine.  However for cold temps, a 10W-30 or even a 5W-30 IS recommended so in that case you would probably be okay.  

Please let me know if you find out anything different.
Michael