Hello everyone,
Just adding my 2 cents. Here is part of a Technical Service Bulletin (#DT-2005-09-21) from Amsoil pertaining
to the original post.
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OBJECTIVE:
To provide information about the effectiveness of tacky/sticky gear oils and relay information that tacky additives,
under high shear forces or heat conditions, are ineffective.
ISSUES:
Some lubricant manufacturers add tackifier additives to gear lubes so they become “tacky” or “sticky”. Tacky gear
oil provides a visual marketing benefit when used in clear, see-through plastic gear demonstration units or “egg
beater” demonstrators. In these units tacky gear oils climb gears or cluster together around the egg beater
demonstrator more than non-tacky gear oils. This property is sold as a benefit to prospective customers.
TECHNICAL DISCUSSION:
Tackifier additives are large molecule components that are not shear stable. When subjected to high shear forces,
they break down and lose their tackiness properties. In order to demonstrate that tackifier additives become
ineffective in service due to mechanical shearing forces, a commercially available SAE 90 tacky gear oil was
subjected to a 20-hour KRL shear stability test. The 20-hour KRL shear stability test is a requirement for automotive
gear oils according to the industry standard SAE J-306 (see KRL Graph).
(graph did not copy and paste, sorry)
After the test, the SAE 90 gear oil lost 10.77% of its viscosity due to mechanical shear. Upon visual inspection, the
tacky properties of the gear oil were severely reduced.
Another factor that affects tackiness properties of a lubricant is temperature. Normal operating temperatures of
(92°C, 197°F) are sufficient to cause the depolymerization of tackifier additives(1). As operating temperatures
increase, tackiness properties decrease to the point they are ineffective.
CONCLUSION:
Effective gear lubrication only requires a thin film of lubricant. Excessive lubricant presents no benefits and, in
some instances, can have negative effects. The perceived benefit of adding tackifier additives to gear oils is to
show how the gear oil climbs or clusters around the gears. Under room temperature conditions, this is easy to show.
Under normal operating temperatures, this does not occur. Gear applications have some of the highest me-chanical
shear rates known. High molecular weight additives break down under these conditions.
Tackifier additives loose their tack ability.
GM, Ford, & Chrysler gear oils were tested for tacky properties. None contained it. Based on this, it
appears that OEM gear manufacturers do not use or recommend tackified gear oils.
Reference:
1.) “Lubricant Additives chemistry and applica-
tions”, 2003, Marcell Dekker, NY., Rud-
nick, Leslie R., Chapter 12, Page 358.
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I am not trying to stir up any heated debates about oil. Some people can respond as if the topic is an attack
their religion. I am just trying to inform about the plastic demo device and why the Lucas Oil climbs. A year
ago I worked part-time job at an Advance Auto Parts and they had the Lucas demonstrator on the counter.
It was fun to see people fascinated by it. I do not believe in gimmicks or miracles in a can. Good oil is
engineered to do a specific job. Adding additives can reduce the quality of any oil - you are mixing chemicals
together without knowing what is in either the oil or the additive.
As for the STP and it's ilk, it is a viscoscity improver. Just to make an easy explanation, let's say you are
using an SAE 30 oil and add STP, basically, you are increasing the viscosity of that oil to be a 10W-30
multi-weight oil allowing it to work more like a 10 weight oil in the cold. I do not think it was ever intended
to lubricate anything by itself, except maybe a straight screwdriver tip help between the thumb and forefinger.
Keep in mind the test is for an automobile differential gear set, which is under tremendous shear forces compared to straight cut gears - that is why some transmissions call for engine oil as a lubricant instead of hypoid gear oil and some even use ATF.
Me, I have a 6" Atlas lathe and at present I am lubricating the gears and moving parts with some out of date synthetic gear oil. It is overkill but, I have to use it on something and was told not to use it in a differential. Gear oils have a shelf life and the additives can drop out of solution and just shaking the bottle will not rectify the condition. Whatever I use, it gets oiled prior to and during its operation. Messy!
