Another engine oil thread, this time about JD diesel oil for marine app.
03-21-2012, 06:45 AM
#11
Registered
Hemanite, the "plasticisers" you are refering to are actually called polymers. They are an additive to control the rate of thinning of oil when oil gets hot. it is these polymers that make a single weight oil a multi-viscosity one.
If an oil blender used cheap polymers, they can shear down and your oil will loose viscosity or "fall out of grade", eventiually reverting back to the original viscosity base oil. Base oils cannot loose viscosity.
Some mulit-viscosity oils, contain no polymers. This is done by combining multiple base stocks of different viscosities to achive a final grade.
Mercury's oil does not have much of a viscosity spread. Little or no polymer is going to be used in the blending of this product, which helps control the shear or falling out of grade.
As far as adding the two numbers together and dividing by 2, short answer, no.
A mulit-viscosity oil meets TWO different grades or viscosities AT 2 DIFFERENT TEMPS.
The number preceding the W,(which means winter and not weight), is the oils cold weather performance of the oil. This related to the oils ability to get pumped to the far reaching corners of the motor at start up. The 25w spec of Mercury's oil is rated at -5 C for cranking and -10 C for pumping.
(For comparison, a 0w oil is rated at -30 C for cranking and -35 for pumping).
The number after the W is the viscosity at 100C, which even though the number is higher, the viscosity is thinner. Remember oil thins with heat and thickens with cold.
The ratings are on two different scales hence the confusion.
The different scale thing also applies to gear oils. A straight 90 GEAR oil has the same viscosity of a 50 weight MOTOR oil.
Once again the above info is "broad brush".
Hope this helps.
Ken
If an oil blender used cheap polymers, they can shear down and your oil will loose viscosity or "fall out of grade", eventiually reverting back to the original viscosity base oil. Base oils cannot loose viscosity.
Some mulit-viscosity oils, contain no polymers. This is done by combining multiple base stocks of different viscosities to achive a final grade.
Mercury's oil does not have much of a viscosity spread. Little or no polymer is going to be used in the blending of this product, which helps control the shear or falling out of grade.
As far as adding the two numbers together and dividing by 2, short answer, no.
A mulit-viscosity oil meets TWO different grades or viscosities AT 2 DIFFERENT TEMPS.
The number preceding the W,(which means winter and not weight), is the oils cold weather performance of the oil. This related to the oils ability to get pumped to the far reaching corners of the motor at start up. The 25w spec of Mercury's oil is rated at -5 C for cranking and -10 C for pumping.
(For comparison, a 0w oil is rated at -30 C for cranking and -35 for pumping).
The number after the W is the viscosity at 100C, which even though the number is higher, the viscosity is thinner. Remember oil thins with heat and thickens with cold.
The ratings are on two different scales hence the confusion.
The different scale thing also applies to gear oils. A straight 90 GEAR oil has the same viscosity of a 50 weight MOTOR oil.
Once again the above info is "broad brush".
Hope this helps.
Ken
Last edited by minxguy; 03-21-2012 at 11:40 AM.
