determning viscosity requirements

[bonnie john]

can someone please tell me how to determine the viscosity required by the manufacturers in their oil recommendations

case in point, my 14 year old harley big twin recommendations are "use 20w50 for temps 20F-100F".

i would like to know if i can check an oils suitability by comparing the oils cts at 40C and 100C, but don't understand enough to do it i.e will a 15w50 be ok to use or is it too thin when it is cold

hope this hasn't been covered before and thanx in advance for your replies, johnny

 

[427Z06]

Here's a quick and dirty.

Match up the last number. So if it says to use 20w50, select something that is Xw50. If it's non-synthetic oil, also match up the first number. So in this case, if it's non-synthetic use a 20w50. If your considering a full-synthetic, the first number can drop a grade or possibly two. So a full synthetic 15w50 would easily meet this requirement. If you want to get into more details may I suggest you do a lot more reading.

Here a good place to start:

http://www.lubrizol.com/LubeTheory/default.asp

 

[bonnie john]

t/y 427z06

does anyone have the link to a recent graph which showed different grades and the heat/viscosity relationship between them

it was a nice color graph and for the life of me i can't seem to find it again

 

[427Z06]

Haven't seen what you're looking for, however, you can use this link and Man'f specs to find the viscosity at a particular temperature:

http://www.geocities.com/CapeCanaveral/3655/VI.html

 

[bonnie john]

hi 427

just studied the chart on the front page

am i correct assuming that i can run any oil which falls with the cts values in my motorcycle?
book says 20w50, so could i use a "thin" brand in winter and a "thick" one in summer?

and then experiment along the lines you suggested, matching the last number and dropping on the first with synthetic

if so, good stuff

 

[427Z06]

Yes.