Garden machinery oil questions

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StevehS3
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Garden machinery oil questions

I am a bit confused about oil grades and types for 4 stroke Honda and B+S type engines. I have been using fully synthetic oil often of a 'better' grade than shown in the manual. Recently an experienced repairer told me to use only mineral oil as that is what they were designed for and as it states in the manual. 
My questions are (i) is there a downside to using synthetic in these types of engine? and (ii) is it ok to go for a wider temperature range oil such as the 5w50 motorsport oil used in the 7. Again, what's the downside?

Many thanks, Steve

Wrightpayne
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Steve,

Generally, I'd go with the manufacturer recommendation, usually 30 grade. If it was low and I didnt have any, I'd use a multigrade to top up.

I guess tolerances in a rudimentary engine are a lot slacker than a motor vehicle and need something a bit thicker. 
 

Ian

garybee
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What type of engine is yours?  Does it have an oil filter (and therefore an oil pump) or is is a splash lubrication system?  If it is pumped 5w50 will be fine but I wouldn't feel confident using that grade in a splash lubricated system.  I'd be dubious about getting enough oil to the big end bearing.  I put 5w30 in my mower engines.  It should help on start up (better than a 30 weight) but acts like a 30 weight does at higher temperature.

Do you know what the numbers mean in relation to oil viscosity (probably should have asked this first)?

garybee
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"I guess tolerances in a rudimentary engine are a lot slacker than a motor vehicle and need something a bit thicker."

It's not as simple as that.  Your car uses a positive pressure lubrication system.  Oil is pumped to where it needs to be so it can deal with thicker oil.  Smaller utility engines don't have a pump so very thick oil may fail to lubricate the big end through the drilling on the big end caps.

StevehS3
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Thank you Ian.

Thank you Gary, The mower is a Honda V-Twin 18hp with a filter and the other is a B+S about 5hp from memory and I think that has a filter too but I'd need to check. I think I understand what the numbers mean. I used 5w30 synthetic at the last oil change. Should I be using mineral oil or is that ok?

garybee
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5w30 (mineral or synthetic) will be absolutely fine in either.  I wouldn't expect the B+S 5hp to have a filter, that size of engine is usually un-pumped/splash lube.  Synthetic will be more able to keep its film strength so isn't something that you need to stay away from. 

The engine repairer didn't give you bad advice as such.  He was playing it safe I'd imagine, you can't go wrong if you stick with what's in the manual.  I'd only consider it bad advice if he told you to use something that would actually cause damage.

StevehS3
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Brilliant. Thank you!

Petethediesel
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For the Briggs use a straight 30 grade mineral oil. The main point with those engines is that the oil quantity is very small and requires changing at 20 hour intervals. Yes that's right, 20 hours.

Pete C