Question(s) about Motor Oil Grades

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ROAD_DOGG33J

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In the manual for my car, it says 5W-30 is recommended. But I think my dad has been using non-synthetic 10W-40 oil the whole time he had the car.

So I looked up oil grades online and it said that manufacturers (like GM) recommend 5W-30, because it's a bit better for fuel economy. But they also mentioned that it may not be good for the engine in the long-run. Yet on various sites, there were some people claiming that the fuel economy claim proved true or that they had worse economy when they switched.

The car currently has about 95,000 miles on it and is mainly used for short distance driving.

So, I guess the questions are: Is a higher-grade oil better for older engines? What grade of oil should I be using? and What are the effects of running a higher or lower grade than is recommended?

Thanks in advance
 
If the manual says 5-30 then run 5-30. I use Valvoline 5-30 dino oil in the Prelude and it has like 93k miles on it. Correct me if I'm wrong but I think that the 5 is just the weight of the oil when its cold and the 30 is when its hot? A thicker oil will just make cold starts harder because its thicker and harder to turn.
 
If the manual says 5-30 then run 5-30. I use Valvoline 5-30 dino oil in the Prelude and it has like 93k miles on it. Correct me if I'm wrong but I think that the 5 is just the weight of the oil when its cold and the 30 is when its hot? A thicker oil will just make cold starts harder because its thicker and harder to turn.

The argument against 5W-30 was that it was too thin (like water) and it wouldn't lubricate and protect the engine enough at low temperatures.
 
If the second number is 30, then it's 30 when it's hot, regardless of whether it's 0w30, 5w30 or 10w30... to a point... there are still slight differences at operating temps, but they're minor.

The formulation and additives of each oil plays a big part... you can have a synthetic 10w40 that's lighter than a dino 10w40...
 
The fact that a 5W30 doesn't protect as well as a 10W40 is simply not true. I would only up a grade if you're having issues with oil consumption or some sort of engine noise (loud unadjustable valves, piston slap, etc.) When you start your car, you want the thinnest oil possible.
 
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