From: rakoczynskij@gtephx.UUCP (Jurek Rakoczynski)
Subject: Valve covers & Mobil 1
Organization: AG Communication Systems, Phoenix, Arizona
Date: Tue, 1 Sep 1992 21:50:49 GMT

Just wanted to post some info about what I found changing the valve
cover gasket this weekend (I only did one so far).  Don't read anything
more into this than what I write!  Questions always excepted.

The valve cover gasket was leaking oil and I had to fix it: there was a
strong oil burning smell inside the truck. I was curious to see what it
would look like under the valve cover after long term use of Mobil 1
with 1 year (~12-14,000 mile) between oil changes.

It's a 1983 Chevy Suburban 350 cid I got in 1985, with 33,000 miles and
oil changes every 2,000 miles.  In ~1986 @ ~40,000 miles, I started
using Mobil 1, 5W-30 and a Fram PH373 (2 qt truck oil filter).  I was
living in the Chicago area at the time.  Moved to the Phoenix area in
1987, and started using 15W-50 and later went to 10W-30.  All my oil
changes where once a year, around Christmas.  Now there's 105,000 miles
on the truck.

The previous owner had fixed the leaking valve cover gaskets before I
pickup the truck by using a RTV silicone (the orange/red stuff, I don't
remember which one that is).  It work for several years.

Well the covers came off pretty easy and the leak problem was readily
apparent; the lower center 4" of silicone was missing.  The adjacent
silicon tapered to nothing when it met this area.  I don't want to say
it was dissolved, but it had the same appearance.  There was some
flaking of little pieces of silicone in the thin areas but other
sections
pealed off the head with easy.  More of it stuck to the rough surface of
the head than was on the cover flange.  After I got almost all of the
silicone off the head, I used "brake clean" to cleanup the oil off the
flange of the head.  Was I surprise when some of the brake clean that
pooled up at the lower edge of the head was colored *ORANGE*.  What
little silicon was left on the head was being dissolved or loosing it's
color to the "brake clean".  I finished clean it all up and than started
looking at what deposits the oil might have left.

The inside of the valve cover was clean except for a thin yellow varnish
like coating.  I washed the cover in gasoline (no flames please :-) ) on
it didn't do much in the way of removing this coating.  Neither did a
spray on engine cleaner.  I didn't try scratching the coating.  I'll try
it when I do the other valve cover in a few weeks.

The head itself also looked clean except for the same coating the was
obvious on the rocker arm ball nuts.  There was no sludge, even on/near
the valve springs.  Looked down the oil drain holes and what I could see
look clean.  The coating on the rocker arm ball nuts did show what
looked like stress cracks starting from the mounting stud and working
2/3 of the way to the edge of the nut, but this was only the coating. 
No visible cracks in the nut.  I'll test for cracks on the other bank
when I do it.

Overall, the engine was clean, absolutely no sludge.  I'll test some
solvents on this varnish like coating.

But a clean engine is not the only requirement for an oil.  I did no
measurements of engine wear.  I also just went to a 6 month oil change
interval, having changed the oil last month.
-- 
Jurek Rakoczynski, AG Communication Systems, POB 52179, Phoenix, AZ. 85072
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