5w30 oil all year round for the northern states 10w30 in summer in southern
Depends on the make, model, and the year of the vehicle which you failed to list.
SAE 10w30 High Mileage any major brand.
Any major brand SAE 10w30 or High Mileage oil if the engine is high mileage. Use API service SL or SJ.
High Mileage, Zinc-enriched 50 weight from Valvoline.
Use the exact weight that is listed in your owners manual and nothing else. It can be synthetic, conventional, or high mileage.
10W30 Unless it is a high mileage engine, use whatever your owners manual says.
SAE 5w30 weight unless the engine is very high mileage which in that case use SAE 10w30.
You should since it increases longevity just like changing engine oil does for the engine.
It depends on the engine. 100k, 200k, or 300k
SAE 5w20 High Mileage oil any major brand. If it is burning oil then use SAE 5w30 High Mileage.
Use SAE 5w20 but switch to a High Mileage oil in that weight. The High Mileage oil will help protect your engine as it has some additives that are benefitial on an engine with lots of miles on the odometer. Any of the major brands are good.
Not necessarily- it all depends upon how well maintained the engine has been, and also whether it's the vehicles' original engine or not. A high-mileage engine that has been well looked after and cared for, will be in a better running condition than a low-mileage one that hasn't. Also, if the vehicle has had a replacement engine fitted, then mileage will be irrelevant anyway as far as the engine's condition is concerned.