Using 5w20 Oil

[Henry Paul]

I have seen a product at AutoZone called Slick 50, which claims to do the
same thing. It's supposed to cling to metal parts better when the engine is
at rest so it doesn't get so badly hammered at startup.

 

[Mickey]

That's backwards:

When cold, 10w40 acts like a 10w
When hot, 10w40 acts like a 40w
snip

It is NOT a 25% change. Don't believe there is any percentage
relationship between various oil weight ratings.

Oil viscosity changes with temperature. For straight weight oil each
weight rating has its own curve visc Vs temp. With multi-visc oils
the additives change the curve so they thin out with temp much less
than straight weight oil, flatter curve. For something like 10-40, a
thin base oil that has the same visc as 10 weight at the cold temp
measurement point will thin out to where it is the same visc as 40
weight at the upper measurement point. (Can't remember what the
temperatures are at the measurement points.)

Mickey

 

[Henry Paul]

Right, so if it is really cold you want a number lower than 10, or if it is
really hot you want a number higher than 20 or 30. Like say 5w30 for winter
and 10w40 for summer.

We have hot summers and cold winters so I run 10w40 in the summer and 5w30
in the winter.

 

[y_p_w]

I remember (decades ago) people in the Montreal Alfa club liked the oil
additive "MolySlip" (with molybdenum disulphide ISTR?) This worked sort of
like a suspended high temperature graphite grease: slippery "plates" of
molecules, which would settle on bearing surfaces and supposedly provided
lubrication when there wasn't much oil in the journals. I remember using
it in my 2000 GTV a couple of times, too. One of the track racers claimed
it saved his engine once when he put a hole in the oil pan and didn't
notice (until the smoke?). OTOH, others warn against additives that might
gum up the works. Dunno. Anybody use anything like MolySlip these days?

Apparently MoS2 is used in assembly lube, and may be present in high
concentration in 5W-20 motor oils, as well as in gear lubes. What I
gather is that the sulfur is corrosive to copper parts. I'm not
sure how much copper/brass/bronze is exposed to motor oil though.

 

[y_p_w]

I have seen a product at AutoZone called Slick 50, which claims to do the
same thing. It's supposed to cling to metal parts better when the engine is
at rest so it doesn't get so badly hammered at startup.

I would stay far, far away from supposed engine treatments from Slick
50, Duralube, or any number of snake oil vendors. BTW - Slick 50 was
bought out by Quaker State, and is now part of Sopus (Pennzoil/QS/Shell).

Check out the 1997 settlement of FTC complaints against Slick 50:

<http://www.ftc.gov/opa/1997/07/slick.htm>

They made tons of misrepresentations about the effectiveness of regular
motor oil regarding startup protection. The anti-wear additives in
most motor oils actually form somewhat of a protective layer during
startup. They've also never proved that Slick 50 (PTFE) actually bonds
to moving engine parts. About the only application I can see for PTFE
as a lubricant is in a grease or spray lube. They no longer make the
claims, but a lot of people will likely buy it based on their previous
claims.

I tried Slick 50 once, and the only thing I noticed was that there was
some hard, brownish crud stuck to the filler cap and the threads of the
valve cover.

 

[Henry Paul]

I've never used any. As far as optimum starting protection, I use a motor
oil with a temperature range suited to my climate zone. My Subie actually
starts with fewer cranks than my Jeep did. That thing could crank for a
solid 7 seconds before ignition. I've logged my Subie ~2 seconds of
cranking.

 

[Juhan Leemet]

Apparently MoS2 is used in assembly lube, and may be present in high
concentration in 5W-20 motor oils, as well as in gear lubes. What I
gather is that the sulfur is corrosive to copper parts. I'm not sure
how much copper/brass/bronze is exposed to motor oil though.

Well, head gaskets are copper, aren't they? I guess they only touch oil
"edge on" in the various passages through the gasket from block to head.

 

[CompUser]

For something like 10-40, a
thin base oil that has the same visc as 10 weight at the cold temp
measurement point will thin out to where it is the same visc as 40
weight at the upper measurement point. (Can't remember what the
temperatures are at the measurement points.)

Except that 40-weight is *heavier/thicker/more
viscous, than 10-weight.

Viscosity increases numerically, with lubricating
oils.