Does anybody know for sure what is the real difference
between 5w30 and 5w-50 oil?

 

lower #'s = thicker oil
higher # the thinner it will be

A 5-30 will start out as a 5 viscosity, the thinnest/hottest it will get is 30 viscosity.


[Modified by Z-07 freak, 3:03 PM 3/30/2004]

 

So acctually this means that 5w-50 will bu much thinner
when it warms up.
If thats true than I should switch back to 5w-30.

 

I always thought it was the opposite...the lower the number the thinner the oil and the higher the number the thicker the oil....straight 50 wgt oil would be a pretty thick oil...5 wgt oil would be pretty thin...
:seeya

 

http://www.autoeducation.com/autoshop101/oil-change.htm

 

From http://www.vtr.org/maintain/oil-overview.html

Multi viscosity oils work like this: Polymers are added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

 

In your comparison....

5W30 : Same consistency as the 50 when cold.
5W50 : Thicker than the 30 when warm and will not pass through some of the smaller holes in seals, gaskets or piston rings that the 30 would. Run in higher mileage engines a lot of the times.

 

note, too, the 5W part is at a very low temp. at ambient temps in most spring/summer/fall climates the 5W50 will be considerably thicker. most oils have published viscosities at 40°C and 100°C, and typical numbers for a synthetic 5W30 are probably 60/10, whereas the 5W50 might be more like 110/16. so them both being rated as a 5W is misleading for most climates, and during the engine's warmup phase.

-michael

 

No, you've got that backwards.

The numbers indicate resistance to flow; viscosity.

The first number is an indication of resistance to flow at 32 degrees F; the second # is an indication of resistance to flow at 212 degrees F.

The higher the number the MORE resistant it is to flow; thus the pressure will be higher BUT the flow will be less.

If you'd like to see a detailed explanation of oil viscosities, you can probably find it on the sites of some of the big engine oil companies, such as Valvoline and Pennzoil.

So, a 5W 50 oil (if there is such an animal) will maintain higher oil pressure when the oil is really hot; higher than the 5W 30 will maintain.

The lower the first number (5W = 'W' standing for Winter) allows the oil to flow more freely in cold temps, making starting the engine easier and allowing better flow to the crucial parts.

Jake

 

i've seen the 32 degree F assertion in plenty of places, but it's not true that i can tell. i was first clued in when examining published viscosities at various temps, so i did more research.

it turns out that the "W" means that the oil passes the 32 degree F requirements set forth by the SAE for winter use. however, the number ratings preceding the W actually designate what the temp should be for the viscosity requirement.

that is (using bogus numbers just to have an example), a 10W has to meet certain viscosity requirements at -20 degrees C, and a 20W at -10 degrees C. this is tricky because it means an oil can actually meet various xW requirements simultaneously. for instance, an oil might be the correct viscosity to me rated as 10W, but also right to meet the 20W at the different measuring temp.

most 0W oils, for instance, are also 5W and 10W oils. in fact, you'll notice the 40 degrees C viscosity on many 0W oils is actually higher than some 5W and even some 10W oils.

what's interesting is that the xW designation has to meet certain minimum low shear requirements at 100 degrees C, but no maximum. this is basically how you get the 2nd number in a multigrade (along with high shear tests), they see what "weight" the oil meets for the 100 degree C test, and tack that on.

here's the API chart, although i don't think it's comprehensive. there are more requirements than this:
http://www.infineum.com/information/viscosity.html

-michael

 

I took it from the Valvoline and Pennzoil websites showing the temps that the SAE and API require in rating viscosity.

You guys can check it out for yourselves and see if you can make heads or tails out of it.

Jake

 

Milage? Year?
I use the Valvoline Max Life. But Mine is an '84 with 87k on it.
Good Luck!
tony