I have a 97 s-10 Blazer with 150k miles on a 4.3 ltr. and started it up the other day with what sounded like a stuck valve. I wasn't in a good mood and didn't realize it untill I was on the road but it stopped before I had a chance to. The next day it did the same thing for at most 5 mins but I had used my remote start and didn't hear it(a neighbor came and got me). I took it to a shop that I now know not to be very good. And they told me to try 20-50w oil and it should be ok. They didn't do anything since it would not make the noise again and has since not. I have never heard of changing oil weight for this. Should I do it? My 92 Blazer went 235K with no problems with 10-30w. Can someone give me a simple explanation of oil weights? Like the difference in 10-30w, 30w, or 20-50w.

I did some looking and found out what I needed to know about oil weights, but still curious if I should use the 20-50 or not? And should I be concerned about my engine I don't what to put a new one into it since I'm looking to get a truck?