Yes you can, but it might take a lot to make a meaningful difference unless
your engine is a big leaker.

Mike
MU-2


"Ben Jackson" wrote in message
news:CQkJb.261117$_M.1211945@attbi_s54...
Let's say you're at a point where you need to add a quart of oil.
You've decided you would like to finish this oil change interval at
a lighter weight (eg you put in AeroShell W100, SAE-50, and now it's
freaking cold). Can you add a quart of a (substantially?) lighter
weight oil (presumably in the same 'series')?

--
Ben Jackson

http://www.ben.com/