by John Baker
Engine sludge.
It’s a back gelatinous substance that wreaks havoc in engines. And
long before the engine’s demise, engine sludge can foul engine sensors
and interfere with performance. Some mechanics call it the “black
death.”
How does motor oil, which is fluid, become a semi-solid paste or gel inside an engine?
How engine sludge forms
Engine sludge is the result of a series of chemical reactions.
The lubricant degrades as it is exposed to oxygen and elevated
temperatures. The higher the temperature, the more rapid the rate of
degradation. In fact, every 18°F (10°C) increase in temperature doubles
the rate of oxidation.
The by-products of this reaction form highly reactive compounds that
further degrade the lubricant. Their by-products react with other
contaminants, forming organic acids and high-molecular-weight polymeric
products.
These products further react, forming the insoluble product
known more commonly as sludge.
What begins as a thin film of lacquer or varnish deposits on hot or cold metal surfaces and bakes into an expensive mess.
The effects of engine sludge
Sludge can block the oil passages and oil-pump pick-up screen,
resulting in oil starvation. Often, the negative effects are cumulative
rather than sudden.
Many engines with variable valve timing (VVT) use
oil-pressure-operated mechanical devices to change valve timing,
duration and lift.
Sludge can plug the solenoid screen or oil gallies
and impact the operation of VVT mechanisms, eventually leading to a
costly repair bill. Sludge reduces efficiency and increases time and
money spent on maintenance.
Synthetic oil helps prevent engine sludge
Fortunately, sludge and varnish deposits are something oil manufacturers can control. Using thermally stable synthetic base oils reduces the rate of degradation (oxidation).
Anti-oxidant additives help reduce the rate of degradation as well.
One of the most widely used is zinc dithiophosphate. Not only is it an
excellent oxidation inhibitor, it is an outstanding anti-wear additive
as well.
High-quality additives fight engine sludge
We can further address many of the issues occurring after the initial oxidation stage.
Additives, such as detergents and dispersants, are commonly part of
motor oil formulation. They help promote the suspension of contaminants
within the oil and keep them from agglomerating.
Detergents, which are also alkaline in nature, assist in neutralizing
acids generated in the sludge-building process. Anti-oxidant,
dispersant and detergent additives are consumed during use.
AMSOIL Signature Series Synthetic Motor Oil, for example, has 50 percent more detergents* to help keep oil passages clean and promote oil circulation. It provides 90 percent better protection against sludge**.
Signature Series Synthetic Motor Oil was subjected to the Sequence VG
test to measure its ability to prevent sludge. Signature Series
produced an oil pick-up tube screen virtually free from sludge. Our
unique combination of detergents and high-quality base oils control
oxidation and sludge to keep engines clean and efficient.
(AMSOIL Signature Series virtually prevented engine sludge on this oil pick-up screen below.)
Severe service invites engine sludge
Equipment operating conditions also influence the likelihood of sludge or varnish issues.
Stop-and-go driving, frequent/long-term idling and operation in
excessively hot or cold weather can increase the likelihood of sludge
and varnish, especially if using more volatile conventional oils.
If sludge has already formed, you can use an engine flush to clean sludge from your engine.
Interestingly, most auto manufacturers note in their owner’s manual
that operation under any of the above conditions is considered severe
service and requires more frequent oil changes.
From a mechanical standpoint, things like adding too much oil to the
oil sump, antifreeze contamination, excessive soot loading, excessive
oil foaming, poor engine-combustion efficiency, excessive blow-by and
emission-control-system issues can all lead to the formation of sludge
and varnish.
By practicing good maintenance and using properly formulated, premium synthetic lubricants, like AMSOIL synthetic motor oil, your vehicle won’t succumb to the “black death.”
*vs. AMSOIL OE Motor Oil
**Based on independent
testing of AMSOIL Signature Series 5W-30 in the ASTM D6593 engine test
for oil screen plugging as required by the API SN PLUS specification.