Why is it bad to mix Synthetics?

[rrrrrroger]

All the synthetic brands say it's okay to top-off with conventional/natural oil. For example using Mobil 1 as your fill and a few thousand miles later topping-off with Pennzoil conventional.

No prob.

But they do not recommend topping-off with synthetics. For example, using Mobil 1 and later topping-off with half a quart of Pennzoil or Castrol Syntec.

Why is mixing synthetic/natural oil, but mixing synthetics bad?

 

[XPR]

Never heard that before.

 

[wbwanzer]

Should not be a problem.

 

[d00df00d]

Maybe because it's a given that you should be able to top off with an oil of similar quality?

Either way, there can be some competition among components in radically different formulations but the effects are usually minor -- i.e. the result is sub-optimal but there's no harm per se.

 

[Gary Allan]

Quote:
But they do not recommend topping-off with synthetics. For example, using Mobil 1 and later topping-off with half a quart of Pennzoil or Castrol Syntec.


If you read this on XOM's site ..can you link us to it

 

[ctrcbob]

By law, all motoroils must be able to mix with all other motoroils. Otherwise, if you had an oil problem while on the road, you would not be able to find the oil that you had to use in your car.

Example; If there was a Group X Synthetic, and you had it in your car, and this Group X did not mix with Group V or IV or III or II, and you needed to add oil to your car for whatever reason, you probably would not find it at filling stations, or wherever you were when you discovered that your oil level was low. When you need oil, you need it NOW.

(An example of non mixing fluids is Brake Fluid where DOT-5 Will not mix with the other DOT Fluids - problem if you need to top off your fluid and the local places don't have it).

 

[mechtech2]

Oils that are graded the same can be mixed with no problems.
That is part of being graded [like SM, SL, etc..].

 

[XS650]

Originally Posted By: ctrcbob
By law, all motoroils must be able to mix with all other motoroils.



Cite please.

 

[PT1]

Originally Posted By: XS650
Originally Posted By: ctrcbob
By law, all motoroils must be able to mix with all other motoroils.



Cite please.


Maybe he means "Murphy's Law"

 

[XS650]

Originally Posted By: PT1
Originally Posted By: XS650
Originally Posted By: ctrcbob
By law, all motoroils must be able to mix with all other motoroils.



Cite please.


Maybe he means "Murphy's Law"

Murphy was an optimist.

 

[PT1]

Originally Posted By: XS650
Originally Posted By: PT1
Originally Posted By: XS650
Originally Posted By: ctrcbob
By law, all motoroils must be able to mix with all other motoroils.



Cite please.


Maybe he means "Murphy's Law"

Murphy was an optimist.


LOL!

 

[dwendt44]

I doubt it a law as such.
It more likely is a custom that became a habit.
At one time, way back when, any oit company that wanted to do business with the federal government and the military had to have oils that would mix or could be used with any other oil.
There was a military spec for that 'mixability'.
The result was that all major brands of oil could be mixed with each other.
Now a days, it's either an old habit or a custom that the oil companies continue. It's all OIL, and the additives are generally similar as well, anyway.
My 2¢

 

[refaller]

I am currently running 3 different synthetics in my car. Have not lost any sleep at all.

ref