Re: Omc 4.3 litre cobra engine oil
There is no shortage of information on the net and in these forums on the differences of various types of motor oil. Multigrade vs straight grade, synthetic vs non-synthetic, pro's & con's of the different additives found in all those different oils. So many 'opinions' & 'bias' can make it hard to distinguish whats best for your engine.
My only advice is to educate yourself the best you can using credible information available to you. If you can find a (genuine) factory OMC service manual, it will recommend the proper oil, and it will be hard to go wrong using that. Keep in mind that there have been a few improvements in motor oil since OMC printed those service manuals.
SAE 30 is often recommended for engines running at higher operating temperatures, in environments above 32 F. Multigrade oil breaks down sooner at high temperatures that SAE 30 but SAE 30 oil is too thick to run in cold starting temperatures (below 32 F). That is why multigrade is used in automobiles, which often run in a wide range of environments, but rarely at WOT.