As your car has been driven 170K, so better start using Thicker oils only.
Please choose any of the following
PTT Performa 20/50 "Its thick & Red Color oil". Very powerful & strong. And change it every 3K.
ZIC Hi-Flow 20/50 "Yellow" color plastic bottle.
Performa's 20/50 oil is thicker than ZIC. I've long experience to use them in my car. And Performa always gives good mileage as compared with zic and keeps engine more happy.
Do not trust Caltex Havoline, Shell, Total, PSO, etc. etc. etc. Because all of these oils are being packed here and their quality has been significantly reduced recently.
Presently this Performa & ZIC, both are good. But use 20/50. Better not to use 10/40 because last owner was already using 20/50. And if you will use 10/40 or similar oil, then it will increase and engine's sound and will make it bit more warm also.
When you go for the oil change, then shop owners keep the "dirty oil" with them. Right?
The companies like Shell, Toyota, Caltex, PSO, etc. mostly buy these dirty oils, "re-fine" them and re-pack into new bottles. That’s why these oils gives low mileages even then what companies recommend to run.
As far as Radiator valve is concern, just visit a local mechanic to seek his advice.
All the best.