I have an 85 mustang gt 5.0 , its low miles, but for being park for month and month without driving, after so many year, I think it damage the valve steam seal... and this year engine was having weak ring from factory. so now it have little blue smoke and its make my oil turn black pretty quick, that tell me its have bad ring. also if I get on it really hard it blow blue smoke. at idle its not bad,but you can tell it have some blue smoke... for now I dont have any trust mechanic that can rebuild this engine the way I like. I know one guy he a very popular mustang restoration , but his shop is 4000 miles away, for now I just want put in some heavy oil to slow the burning a bit for as long as possible, until I find an trust mechanic to rebuild it right. its currently using 10w30 mobil 5000 and FL1A oil filter. I was thinking some shell diesel 15w40 ... thank you every one.