nothing thicker than regular motor oil is meant to go into a crankcase...
I have seen it in some cases CAUSE oil leaks due to the increase in oil pressure...
all these motor honey or lucas engine oil treatments just mask for at least a while a problem that is overdue..
they make a great product.. the whole line of lucas is the only stuff I use in anything... EXCEPT the engine oil stabilizer...
its a ghetto fix... as long as you know that going in, use away... and just be sure to buy it form Nu Way!!!