What’s what with oils?

Canal Boat - - Ask The Experts - MAG­GIE ALLEN, via email TONY REPLIES…

QWe need oil for a petrol gen­er­a­tor and the mark­ings on oil con­tain­ers are con­fus­ing. The rec­om­mended oil seems to be AP1, SE, SF, SG, SH, 10.30, but all we can find lo­cally is a semi-syn­thetic ACEA A3/B3 API, SL, CF. Would it be okay?

There are two parts to the way oil is des­ig­nated, one re­lates to its vis­cos­ity or ‘run­ni­ness’ and is a stan­dard set by the So­ci­ety of Au­to­mo­bile En­gi­neers ( SAE). The higher the num­ber, the less ‘runny’ or more vis­cous the oil.

By the 1960s mono-grade oils ( SAE 20, SAE 30 and so on) could no longer pro­vide op­ti­mum lu­bri­ca­tion, so multi­grades were de­vel­oped. Th­ese have two vis­cos­ity num­bers sep­a­rated by a W so we get SAE 20W50 or SAE 15W40. The first let­ter shows how ‘runny’ the oil is when cold and the se­cond when it is hot. The oil does not get thicker, it just thins more slowly as it heats up than a mono-grade oil. So it looks as if you need an SAE 10W30.

The se­cond part is a set of per­for­mance stan­dards. There are two stan­dards bod­ies, ACEA ( Euro­pean Au­to­mo­bile Man­u­fac­tur­ers’ As­so­ci­a­tion) and API (the Amer­i­can Pe­tro­leum In­sti­tute). API has a log­i­cal pro­gres­sion sys­tem. The first let­ter tells you what en­gine type the oil is de­signed for so, if the two or three char­ac­ter des­ig­na­tion starts with an S, it’s for Spark ig­ni­tion (petrol) en­gines. If it starts with a C, it’s for Com­pres­sion ig­ni­tion (diesel) en­gines. Some oil

Ameets the cri­te­ria for both en­gines so you find API specs start­ing with both S and C. If the oil is for your boat you con­cen­trate on the Cs and if it’s for a petrol gen­er­a­tor, con­cen­trate on the Ss.

What fol­lows the ini­tial let­ter is an­other let­ter or some­times a let­ter and num­ber that de­fines the per­for­mance stan­dard. The fur­ther up the al­pha­bet the let­ter the higher/bet­ter the oil per­forms. Nowa­days, pure min­eral oil sim­ply can­not per­form well enough for some en­gines and has to be pro­duced in a fac­tory, so oils for high per­for­mance en­gines tend to be known as fully syn­thetic or syn­thetic.

Oils for more mod­est en­gines are based on min­eral oil but have chem­i­cals added to meet per­for­mance stan­dards. Th­ese are lsemi-syn­thetic.

So, you are look­ing for an SAE 10W30 oil in API SE, SF, SG, or SH. The oil you quote would ap­pear to be of a too high spec­i­fi­ca­tion for your gen­er­a­tor but, be­ing a petrol en­gine, I doubt it will do much harm apart from to your wal­let. You also do not give its SAE (vis­cos­ity) des­ig­na­tion. Do­ing a Google search shows most 10W30 oils are ex­pen­sive syn­thetic oils. If you do not want to get it mail or­der and have no time to visit out­lets such as Coun­try­wide Farmer’s Stores and Mo­tor Fac­tors, I sus­pect the best you can do is to use a 10W40 in API SE, SF, SG, or SH oil. This will be the cor­rect vis­cos­ity when cold but a bit thicker than that spec­i­fied

when hot.

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