How does multi weight non detergent motor oil work?

April 29, 2013 12:07 AM

I seen this oil at home depot called "Powermate Non-Detergent 4-Cycle Engine Oil - 10W30" my oil knowledge is at a beginner level but I thought multiweight oils were a emulsion. How do they make a 10w30 oil if there is no detergent in it?
posted by john123357 to Home & Garden (7 answers total)

No, not an emulsion. The detergent in motor oils is to clean the insides of the motor. You don't want it in a motor that isn't built for it for metallurgy reasons.

Multi weight (viscosity) oils are (basically) a mixture of two oils. So a 10w30 is a 10 weight motor oil with other molecules mixed in that are temperature sensitive. When they are at room temperature, they are coiled in into little balls and when they are at motor operating temperature they uncoil and act like sticks. Which modifies the viscosity of the 10 weight oil so that it acts like a 30 weight oil.

In reality, all it does is slow down the rate of thinning. A 10 weight oil at room temperature is still WAY thicker than a 30 weight oil at engine temperature.

(Greases, however, are emulsions as far as I remember. Oil, soaps and sometimes clay-type stuff to make it thicker.)
posted by gjc at 2:26 AM on April 29, 2013 [1 favorite]

Response by poster: so what kind of molecules are mixed in that are temperature sensitive to create that effect?
posted by john123357 at 2:45 AM on April 29, 2013

Viscosity index improvers are often used. They are polymers that swell as temperature rises, offsetting the decrease in viscosity of the base oil.
posted by exogenous at 4:45 AM on April 29, 2013

I found gjc's info intriguing. :) here is a page I found with good information:
http://www.blackstone-labs.com/oil-viscosity.php

And explaining the viscosity improving molecules:
http://www.machinerylubrication.com/Read/1327/viscosity-index-improvers

Lots of big molecules respond to temperature like this; proteins, for example, which is why we cook them.
posted by Made of Star Stuff at 4:46 AM on April 29, 2013

Response by poster: What is the chemical name of the polymer they use to make it a multi-weight oil?
posted by john123357 at 5:16 AM on April 29, 2013

The classic engine oil viscosity index improver, first introduced in the 70s, is olefin copolymer (OCP). HiTEC 5825A is an example of a modern OCP formulation. Other complex polymers are used as viscosity index improvers nowadays as well.

You might want to take read Bob is the Oil Guy's What’s in your Motor Oil.
posted by RichardP at 6:08 AM on April 29, 2013

Response by poster: So if they are adding olefin copolymer which is a type of plastic wouldn't the oil I listed earlier "Powermate Non-Detergent 4-Cycle Engine Oil - 10W30" which is advertised as a petroleum based oil actually be a semi-synthetic oil?
posted by john123357 at 6:51 AM on April 29, 2013