413 industrial... oil?

industrial 413. prettty much stock. fuel injected tbi. what oil should i use? i swear by synthetic, but only in new motors?? i hear high zinc is good, but i also like thick oil. i work it hard in a truck. with a granny 4 speed. so..... i usually go Quaker State Synthetic 20-50. is that good??

A diesel oil with zinc is good. SYN ? ... I think it is uNnecessay.

I use the napa fleet 15/40 oil

also run a lot of straight 30 or 40 weight in the older 318

older flat cams could do with all the zinc you can get

I went roller so its much ez for me,still run the 15/40 in it

Kendall GT1.We run it in all the early cars and have for years.I also run it in my Harleys.Rocky