While picking up some 0w-40 Mobil 1 (still on sale at Advance Auto $4.77). I was told that the 5w and 0w was actually the same thing. He suggested that 0w would have 0 viscosity. Is he an idiot or is there anything to this? I've never heard anything like this before.

 

they are not the same thing. Mobil1 does have a 5W-40, FWIW, but it's made for diesel trucks.

 

"W" means winter. In winter weather the 0W oil will flow like a 0W oil, and the 5W will flow like a 5W oil and a 10W will flow like a 10W oil just until the engine warms up.


http://www.synthetic-oil-tech.com/d....weight_oil.htm

 

I'm going to go with idiot on this one. If his first statement were true, then the 5W would also have zero viscosity according to his second statement. Zero viscosity would imply that the oil is a solid when cold and would not flow at all until heated up to a certain temperature. I don't think many car manufacturers would recommended using an oil that would provide no lubrication during initial engine warm up.

 

check out this link that describes the SAE grades:

http://www.texacoxpresslube.com/carc...viscosity.html

0w can be pumped and cranked at a slightly lower temperature than 5w. that is the biggest difference. the w component of the oil's viscosity is all about getting the engine started when it's -40 C (and maybe even -40 F, lol). for a multiviscosity oil, the 2nd rating number, e.g. "40" is what matters once the engine is starting to warm up. note that at high temperature (100 C) the viscosity must only meet a minimum threshold to meet the specified grade for "w" lubricants. the specification for kinematics viscosity is the same for both 0w and 5w, which might be what the advance guy really meant to say.

 

Mercedes is phasing out 0W-40 Mobil 1 in favor of 5W-40 Mobil 1. AMG has not yet endorsed the oil. We will continue carrying both weights in bottles but will switch to 5W-40 in bulk.
$4.77 is a good deal. We get requests on a daily basis to ship it out at $5.50 per qt.