oil question

[lathehand]

Just wondering what the harm if any would there be using quicksilver full synthetc pwc tow cycle oil in my 1977 1500 merc and my 90 power trim engines.The juug says not for tw-c3 engines .I don't even know what a tw-c3 engine is. I remember back in the day I just used any 30 weight non deturgent oil and I never lost a engine to oil problems. I used the same 50 to 1 ratio same as this container is saying.Also I was wonering on the front of the jug it says synthetic 2 cycle oil and on the back it says contains lubricating oil and petroteum products so what is it? A friend's wife got me 2 gallons never opened at a yard sale for only 5 bucks . I'm not saying I'm cheep I'm just bsaying I got short arms and deep pockets LOL