Forgive me for being stupid;
What does the 5 and the 20 stand for? I think that 5W is thinner then 10W (but how is it calculated?) also what is the difference between 20 and 30? (ie 5w20/5w30). Any help would be appreciated.
You are on the right path. I forget the precise method to determine the thickness, you can probably get it from a web search or one of the guys who frequents this forum claims to be an oil expert.
Essentially the weight spec is ##W##. The ##W being the viscosity of the oil at freezing temperatures, I think usually at 32degrees F. The number after the W is the summer or above freezing weight and I think it is usually at something like 70 F.
Lower numbers mean thinner oil essentially which means easier flowing.
So, a 5W30 would be thinner at freezing than a 15W30 for example, but at normal operating temperature they would be the same viscosity, ie 30 weight.
Always follow the manufacturer recommendation but in general... If I lived in a moderate climate I would probably go with a 5W30 to maybe 15W40 year round. If I lived where heck freezes over, I would probably try 0W30 which is probably a synthetic anyway. If I lived in Saudi Arabia, I would probably go with 20W50 year round. Engines are different etc so these figures are very general.
I use synthetics and I don't worry about temperature ranges since they are typcially good from below 0F to almost the point of the paint on the engine catching fire ;^)
I have tried 0W30 Mobil 1 in a chebby and it made a fair amount of noise as compared to my normal 5W30 Mobil 1. I use a 10W30 Valvoline syn in my 94 460 that I use to tow, mostly because I don't think Valvoline had 5W30 syn when I changed to syn on that engine in 96.
Heavier oils have some advantages in warm weather. They seem to cushion the internals better, and seal loose rings better than thinner oils. The disadvantage is that they can decrease mileage a bit(single digit %s usually) and in cold weather they do not flow as quickly so your engine may be oil starved. I have also heard that the thick oils in cold weather can cause some lifters to not pump up properly and there is the occasional exploded oil filter.
In my opinion, an engine in good condition in moderate temperatures say 30F to 100F is plenty happy with 5W30 to 15W40. If you run synthetic, who cares what temperature it is.
I have used syn since 1980 in GM, Nissan, Ford vehicles and yard equipment in sub freezing to blazing heat and towing with no problems. Course a good modern dino probably would do just as well, but back in 1980 things were different. I did use Valvoline dinos since about 1971 to 1980 with no problems, except for once when I got into freezing conditons with 20W50 which turned into taffy in the crankcase.
depends what kind of motor youve got. for old pushrod V8's 10-30 is usually better than the 5-20. but it depends what kind of weather your in to, id say during the winter for a pushord engine 10-30 would be good down to 15 or 20 degrees. for pushrod engines during the summer 100+ run 15-40.