Why do you need to change oil in sealed machinery?

[Popinski]

Sorry, I don't know where to put this question.

I've seen a lot of industrial machinery that says it is sealed and the oil, grease, any lube, never have to be changed.

Some, however, like the rear end of a RWD car, need to be changed out.

If it is a sealed system where contaminants are non-existent, why change the oil? Oil never loses their lubricity!

 

[JHZR2]

Define sealed. Is there still some air exchange to allow for expansion/contraction, like in a diff? Then there is the potential for oxidation and moisture to be present.

Wear metals are also an issue - buildup.

Some sealed components, like suspension parts, are sealed for good, have no headspace, and are truly lifetime lubed.

 

[Dupree]

agreed, that is like the sealed transmissions, unless it is absolutely air tight there is possibility for contamination. Wear does occur on metals also resulting in contaminants even in a sealed environment to be presented. This in my opinion is why the new "sealed" transmissions are a set up for early failure. I understand they are preventing mis-fills and wrong fluid choice which can cause premature failure. But a properly maintained transmission with correct fluid and levels with periodic fluid changes is going to outlive the same unit in a sealed drive the original fluid forever transmission any day.

 

[bullwinkle]

One example is sealed refrigeration system compressors-operating in the absence of any air (normally), they will last until something breaks, burns up, or seizes without regular oil changes.

 

[Quest]

Originally Posted By: Popinski
Some, however, like the rear end of a RWD car, need to be changed out.

If it is a sealed system where contaminants are non-existent, why change the oil? Oil never loses their lubricity!


2 things of note:

(1 ) RWD drives rear differentials is not "sealed" but vented. This is required for thermal-expansion related venting.

***of course, air and other contaminants can get in from the vent hole/lines because of that***

(2 ) regardless of whether the lubrication system is "sealed" or not, additive depletion, etc. still happens as time goes by.

So, in summary, nothing lasts forever and lubricants should be changed out on a periodic basis (IMHO).

Q.

 

[gathermewool]

Put simply, heat + air = degradation by oxidation. Contamination through vent paths and wear materials is also of concern. With that being said, many probably change diff fluids when inspection for proper level would have been sufficient. I belong to that group.

 

[Popinski]

Obviously I have a lot to learn.

Thanks for the answers.

 

[JZiggy]

Some applications use very specialized lubricants like flourinated fluids which retain their properties for much longer because they are very stable. I believe this is more for things like vacuum pumps. I don't know much about them, but interesting anyway.