Sludge

[FL_Rob]

Has anyone ever actually analyzed sludge?The chemical properties,what is sludge really?Condenced/dehydrated oil?or what?

 

[SuperDave456]

Pretty much it is worn out oil.
People who go 10,000 miles and up on bulk dino oil leave deposits of leftovers all over the inside of their engines. As the oil cools off after each run contaminates fall out of suspension and begin to bond to the interior surfaces.
Over extend your oil over several OCIs and you get layers of burned junk that looks anything from black boogers all the way to black charcoal.

Ive seen engines that when you take off the valve cover there is a perfect cast of the valve covers in carbon directly under them after several years of long OCI's. In this case the engine made noise, but still ran.

In another case I had a woman bring a 1 year old Dodge Neon into the shop asking about engine noise. She had gone 30,000 miles on the factory fill and she needed a long block. I went back to school a week later and never found out if the Dealership covered it under warranty.

It is just oil in another form.

 

[FL_Rob]

I dont know how an engine could run at all like that,in older pushrod designs,the lifters would start tickin' and sticky valves,rings, etc.I guess ohc engines have a greater margin of destruction.So, some engines really are sludge sensitive,others as long as theres 'liquid sludge' pumping through

 

[rclint]

I have seen sludge form in gear boxes, and such from lack of oil flow. If you have a corner, a crevice etc that oil does not flow well around/over that is where sludge tends to form. I don't think it's 10,000 miles on bulk dino causing sludge problems, I go 7500 miles on dino in my 02 accord I have no sludge problems, and I have went over the 7500 miles a couple of times.

I think in the past sludge was from the oil itself, you will also notice that some engines like Toyota's tend to be sludge prone. I don't have a clear answer of what sludge is, however it seems it's caused by heat, and looks like the oil being dehydrated/cooked.

 

[oblivion]

Sludge is mostly carbon and whatever metals are in the additive package of the oil after all the volatiles have been burned off. Plus whatever non volatile solids are in the gasoline that have accumulated in the oil from blowby or leakage. Maybe add whatever the engine inhaled that made it into the oil.

To demonstrate: Put some (cooking) oil in a frying pan. Fry up some hamburger, chicken, whatever. Leave the pan on too high of heat for too long. You should now have a perfect example of what sludge is in the bottom of the pan to try and scrape off: Toasted oil and bits of whatever else was there at the time embedded in it. (not recommending that we fry up out burgers in a good synthetic)

 

[Wilhelm_D]

Originally Posted By: FL_Rob
Has anyone ever actually analyzed sludge?The chemical properties,what is sludge really?Condenced/dehydrated oil?or what?


Oil sludge is the breakdown product of over-stressed motor oil adhering to various particles in the oil.

The stressers are primarily heat and contamination. After prolonged exposure to high heat, engine oil begins to oxidize and break down, creating a gelatinous substance which agglomerates around foreign particles such as bits of carbon, dirt, or even some oil additives like ZDDP.

Since sludge acts as an insulator and decrease oil flow through small passages, it increases the chance of formation of more sludge.

Causes include poor quality oil, too infrequent an oil change interval, increased engine temperatures due to Federal fuel economy requirements, and lack of cooling system maintenance.

Prevention includes use of synthetic motor oil (which resists oxidation and high heat), more frequent oil changes, and proper cooling system maintenance.