|Originally posted by Robertzep2:|
I read somewhere that GM issued a service bulletin that all Fiero's with over 50,000 miles should be using 10w30 and not 5w30
I'm not aware of any such TSB. There was
a TSB issued in the late 1970s or early 1980s advising against using 10W40 in GM engines for which 10W30 was specified.
|Originally posted by no2pencil:|
I was under the impression that 5w30 vs 10w30 was based on time of year & location. Cold vs warm climate.
The "30" is a rough index of the oil's viscosity (i.e. "thickness") at normal engine operating temperature (~100°C/212°F). The "5W" and "10W" are similar indices of the oil's viscosity at cold ambient temperatures (i.e. under cold-start conditions ... ~-18°C/0°F).
Both 5W30 and 10W30 will have the same viscosity at normal engine operating temperatures, but the 5W oil will provide better lubrication for cold starts ... the lower the start-up temperature, the greater the benefit from the 5W oil.
See this thread
for an excellent discussion of the topic. Also see Motor Oil 101
for a more rigorous (if long winded) exploration of the subject of selecting the proper motor oil viscosity for different driving conditions.
[This message has been edited by Marvin McInnis (edited 06-16-2014).]