Need help translating this.

[dave1251]

"If you have ever rebuilt a motor you know about golden brown varnish and sludge. Varnish is a tough adherent oxide or carbonaceous material that coats surfaces. Hot surfaces and/or time will often cure varnish to a hard/brittle consistency. Sludge, which is sometimes a precursor to varnish, is soft and sticky and can move about the crankcase until finally coming to rest at sump bottoms, troughs, strainers, filters, and narrow fluid passages. Other common words for varnish and sludge include deposits, lacquer, tars, pigments, gums, and resins.

Air bubbles begin circulating in oil due to overfilling, low levels or high revving (over-agitated). Air bubbles can cause failure of the oil due to the condition known as Pressure-induced Thermal Degradation (PTG). This can both introduce air into the oil and inhibit efficient detrainment of the air (degassing). Also, aged and water-contaminated fluids lose surface tension over time, resulting in air bubbles reducing in size when agitated. The smaller the air bubble, the slower its trip to the surface."

This is just something I read, I will be honest I am having a problem wrapping my head around this. To me it looks like someone is throwing a bunch a definitions with a theory together. Sludge before varnish? It seems everyone that has varnish on your engines surface had sludge on there before.

 

[yonyon]

I've always thought varnish was more typically a polymer material while sludge is mostly graphite with possibly other misc. schtuff mixed in. If that's so, it's hard to believe sludge would be a precursor to varnish while the inverse might work. Is this not so?

 

[dave1251]

I just feel more unintelligent every time I read it unfortunately when someone posts something like this on the internet their word becomes gospel because the majority of the reply's to this from the members on that forum are lining up to eat this gospel like some our overweight brethren like to eat at a buffet.

 

[dave1251]

I am sorry I should be more specific I have read where (PTG) is referred to the process in which an air bubble transitions from a low pressure zone to a high pressure zone. But I can not grasp how this causes a motor oil to fail and this is what causes sludge or how this was written causes sludge then varnish.

 

[bullwinkle]

Originally Posted By: dave1251
Air bubbles begin circulating in oil due to overfilling, low levels or high revving (over-agitated). Air bubbles can cause failure of the oil due to the condition known as Pressure-induced Thermal Degradation (PTG). This can both introduce air into the oil and inhibit efficient detrainment of the air (degassing). Also, aged and water-contaminated fluids lose surface tension over time, resulting in air bubbles reducing in size when agitated. The smaller the air bubble, the slower its trip to the surface."
This sounds a little Bull Shiitake-ish to me-just having air bubbles in your oil is not going to have anything to do with "pressure", or "thermal" i.e. HEAT degradation-this "PTG" sounds awfully similar to shear!

 

[dave1251]

Also I understand Oxidation if left unchecked would cause varnish. But I do not understand the sludge turns into varnish.

 

[Kestas]

Who wrote that? author and credentials.

 

[Bob Woods]

This appears to be the source, http://www.northamericanmotoring.com/forums/r56-hatch-talk-2007/226209-oil-change-intervals-2.html

 

[Kestas]

Dave, I've seen many people talk well beyond what they know.

Don't get a migraine trying to understand that passage.

 

[dave1251]

Yeah Bob that is where I found it. Kestas thanks, shortly there afterwords me and the family went to see the latest Muppet's movie. 3 minutes into the movie I remembered why I did not like the Muppet's while I was a kid. My kids did not seem to enjoy themselves either I would prefer to watch Sesame Street for 2 hours.

 

[Shannow]

Air bubbles can cause thermal degradation, as they can "microdiesel" when they go into high pressure parts of bearings, or hydraulic cylinders come to a rapid halt etc. it can literally cause combustion byproducts.

When you pull apart a turbine and see the following, you know that air and water are not under control. You can see where the oil has undergone rapid pressure rise, and "stuff" has happened to it...that in itself is scary, but it alos means that it will be plating out in cooler areas (like the governor and control valves).

A couple of good reads on varnish formation, still pertinent to automotive, which is worse with radicals introduced via blowby, mixed metal manufacture, and many many more heating/cooling cycles..

http://www.machinerylubrication.com/Read/998/varnish-formation
http://www.power-eng.com/articles/print/volume-109/issue-8/features/vanishing-varnish.html

 

[mechtech2]

Many many engines have varnish - slight to moderate, and have no sludge issues whatsoever.
I note that hot running engines are prone to varnish .
Faulty PCV systems can contribute to both sludge and varnish.

 

[dave1251]

Thanks for the info.