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
So, did GM ever issue such a service bulletin?

Not sure and it really doesn't make sense as the 5-30 oil is just about standard for almost all cars now. 5 is for startup lube and I would think an older car with more miles on it would be needing that.

But I did find this,

http://www.tsbdata.com/tsb/...ero-v6-173-2_8l.html

Hope that helps

Steve

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Technology is great when it works,
and one big pain in the ass when it doesn't



Detroit iron rules all the rest are just toys.

if you're sure that your pressure gauge is accurate (check pressure with a mechanical gauge and compare), stay with the 5 w 30 as long as your pressure stays in the 15# range at hot idle. It will probably stay just around 40# at road speed. If pressures drop, first go to 10 w 30 then to 20 w 40.

haven't heard that one, but depending on your climate, it shouldn't be an issue.

I was under the impression that 5w30 vs 10w30 was based on time of year & location. Cold vs warm climate. If that's true, suggesting a single standard wouldn't make much sense.

quote 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.

quote 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).]

5w30 is common on new cars. Tolerances are closer and they need it to get mpg the gov wants. Id never use 5w30 in a car older than 2000 unless the manual says to. I might if the daily temps were in single digits most of the time. I generally even use 10w30 or 10w40 in my newer cars. 5w just dont seem good enough to me just as temps of over 230* are too high. Im all old school...I want oil to cushion bearings and cylinders and running temps that arent already over boiling. Ill give up 1/2 mile per gallon of gas to make an engine last an extra 100K.

I did not ask this question based on a oil pressure problem my car is having. On a mechanical gauge, mine reads approx. 30 PSI at hot idle. The reason that I asked about this Service bulletin is; I had answered someone else's question about low oil pressure. I remember reading about this years ago, and could not for the life of me remember where I had read it. So I thought that I would throw it out there. Thanks for the replies.

First time I have heard anything about that. With today's oil's being mostly synthetics you should be just fine by using high mileage 5W30 full synthetic oil. I live in colorado so the altitude is rather high but I still use 5W30 with no problems at all.

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The wetter the better

[This message has been edited by zzzhuh (edited 06-16-2014).]