First off,20-50 wt is used for AIR COOLED engines,NOT water cooled engines,it is to thick at start up.Second FOLLOW your manufacturers specs,the company engineers know what they require.3d, semi synthetic to me is a waste of money.I use FULL synthetic oil in all 19 motorcycles I own,my lawn mower and my cars and truck.The reason is less break down from synthetics than dino oil,much better shear rate,better lubricitymuch better ability to handle higher engine oil temps without breaking down.Semi will have MORE breakdown and deposits than full syntheic less shear rate (very imortant) less ability to handle heat (not to important on water cooled engines).Use the lightest oil you can safely use.5-30 on a tight engine.10-30 on an engine with higher miles that has never run synthetic till you are sure you won't have leaks (synthetics DO NOT CAUSE SEALS TO SHRINK,synthetics are such good detergent oils that they tend to clean out the deposits and sludge from the mineral oil and thats where the leaks come from.I use ONLY Mobil 1 or Shell ROtella synthetics.If I could get it around NJ I'd also use Mobil DElvac synthetic.STAWAY FROM CASTROL SYNTEC,ALWAYS scores lowest in tests on synthetic oils.
