Should we be using lighter weight oil?

Joel A. Frahm frahm at jilau1.Colorado.EDU
Sun Dec 29 12:01:25 EST 2002

I believe that Ford is recommending 5w-20 for many motors that used to
require 5w-30:

I don't know how/if the new 5w-20 protects as well as 5 or 10w-30 did.

I can't imagine why they would make this recommendation for cars they no
longer have under warranty or need to keep fuel consumption does for CAFE
standards, unless it is somehow beneficial.  I know my Audi manual does
not recommend high speed driving for long with the thinner "winter" oils
in the crankcase.

I had a 32v 4 cam Ford V8 for a few years, it was important not to use
heavy oils in this motor to prevent cam wear on startup.  Thicker oils (at
least thick dino oils) take too long to pump up to the cam bearings.
There were also a few cases of popped oil filters due to excessive
pressure on startup with cold 50 weight.

Personally I feel that with synthetic oil you can use a heavier weight in
winter due to the exellent cold pumpability of synthetic oils.  However I
also think that synthetics do not suspend particles as well as dino, so I
blend them.  Generally I blend oils from the same company (even though the
specifications require full compatibility among different brands.)  In the
winter I use 2/3 synthetic to 1/3 dino or thereabouts.

I haven't used the Audi in bitter cold yet, but if your needs include long
high-speed travel and very cold startup I would recommend an engine heater
rather than very thin oil, and good synthetic oil for the coldest months.

Joel Frahm <frahm at>
University of Colorado, JILA

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