i have an oil question pertaining to my '99 Scab 5.4L. it has about 112,000 miles on it, and my brother has been putting M1 10W-30 in it for the past 3 years. with the winters here in chicago, i wanted to knock it down to M1 5W-30 (which is the recommended anyway). this engine runs great and has had M1 in some form since 6,000 miles, so will changing the weight do anything harmful to the motor? i have read on this site many times that there is little difference b/w 5W and 10W, but wanted to run it by everybody. thanks for taking the time.

 

use whatever factory states u should use which is either gonna be 5w-30 or 5w-20 for ur engine

 

Changing weights usually does not cause problems.

Problems usually occur when the engine has been running dino for a long time then you switch to synthetic oil.

So go for the switch, shouldnt be a problem

 

A few points about oil...

-- Run whatever weight Ford recommends depending on the air temperature where you live, ie - thicker in the desert, thinner in the winter. See your owner's manual.
-- 5w30 in plain english means "pours like 5 wt, protects like 30 wt".
-- Use quality oil, whatever grade. There's no substitute for good oil, no matter the grade or the change interval.