oil change question

[Hog]

Originally Posted by soslow

A few days ago I brought my 1990 ZR-1 in for an oil change and specified to the mechanic that I wanted Mobil 1 High Mileage oil. He replaced the 8.5 quarts and gave me a half quart to bring home. When I got home, I noticed that he put in 5w-30 weight oil instead of the 10W-30 that the car calls for. Is this a big deal? It is synthetic and has some 10W-30 from the last oil remaining that doesn't drain out. Any thoughts?
The car only has 11,000 miles on it.

The 5W30 will have the exact same viscosity at 100ºC/212ºF as the 10W30 oil will. The difference will be during cold start temperatures, where the 5W30 oil will flow easier than the 10W30 will. Your engine may in fact have a decrease in cold start wear as the 5W oil will flow easier at that lower cold start temperature.
Since it sounds as though you have the luxury of being able to drive your Z in the Winter(I envy you) simply start up the Beast and drive it. IMO No need to warm up an EFI car, nothing gets you engine up to operating temperature faster than gently driving it. Having it sit there and idle merely prolongs the amount of time that elapses before your engine reaches operating temperatures. Very little wear occurs during normal driving, most of it occurs during cold starts.

OEMs have been decreasing the cold temperature viscosity numbers over the years. In the 90's it was 10W, then went down to a thinner 5W**, and now is down to a 0W for many OEMs.

IMO In regards to the LT5. I feel that its more important to provide an engine oil that has the proper high pressure lubricants package for the lobe followers/lifter, chains and the large chain guide surface area(as well as other areas)as there are not a roller type, than worry about the cold(Winter) viscosity number of an engine oil, esp. a synthetic oil. The synthetic oils that some people use have much better cold flow properties than conventional oils do.
And at the other end of the spectrum temperature wise, synthetics are superior in terms of high thermal stability. This would be of great concern IMO in an early car with OEM turbocharging such as the Callaway Corvettes rpo B2K. Though they didn't use flat tappets, they did have rocker arms that exhibit galling above 6000rpm(not an issue in OEM parameters).

Of course all of my opines here excuse non of the issues that you should have with the oil change business that provided you with an incorrect fill.