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Message: <blockquote data-quote="E46Fanatic" data-source="post: 347887" data-attributes="member: 81">I sometimes wonder whether its sludge or bitumen which ends up in the engine.  Its known the N52 runs hotter than the M54 and the oil disapearance issues seem to be isolated on our climate conditions (hot and humid).  Came across this letter.. here : <a href="http://www.schleeter.com/oil-sludge-letter-01.htm" target="_blank">http://www.schleeter.com/oil-sludge-letter-01.htm</a>.  Any oil men or petrochemists wanna give their inputs?  Calling Schwepps or WCC?"" Dear Norris,I wish I had stumbled across your brilliantly informative site much earlier. However, I have been carefully studying the failure of my 1997 LandCruiser engine (135,000 Klms/around 85,000miles) for over a year and I have derived information that I trust you'll find useful, even though it is at odds with some of the underlying assumptions of your work on "sludge". By the way, in parlance I am more accustomed to and from my experience pre-PCV systems and detergent/dispersancy factors in motor oils, "sludge" is a combination of soot (from blow by) and moisture and it gathers in the sump as grey to black muck that can be readily washed out with kerosene. It is nothing like the material that accumulated in my engine.The material that caused my engine to fail proved to be "Bitumen" (yep, the type of material that road surfaces are made from) and definitely not sludge in the my traditionally understood sense.It was not formed through chemical interactions and was not caused by poor maintenance. It had nothing to do with ash content, soot, or moisture. Moreover it formed from pyrolization of the organic fractions remaining in the base oil from the refining process.The oil mist generated by the moving parts smoked off on contact with excessively hot surfaces within the crankcase and rose within the engine internals to condense as bitumen on cooler internal surfaces (e.g. cam cover and timing chain cover, and that which passed through the PCV valve condensed on the inner surfaces of the inlet manifold and that found its way down to coke up the inlet valves). It had nothing to do with the efficacy of the PCV system or any other contaminants.One of the tests I did with thermo couples showed that a thin film of the oil I was using will smoke off a 140 degrees Celsius metal surface. (This is not the same as Flash Point). Bearing in mind that the usual coolant mix under pressurization can reach more than 130 degrees Celsius without boiling, it doesn't take much for the internals of the crankcase to exceed 140 Degrees under some operating conditions if the cooling system and temperature sensing system isn't up to the job and allows heat soak build up without temp gauge indication.As it turns out, the evidence overwhelmingly and irrefutably shows that the block has been operating at excessive temperatures because the cooling system cannot transfer the full potential heat load up via the cylinder head through the thermostat and radiator for cooling.The mass and surface areas of the aluminium cylinder head, cam cover and inlet manifold do a magnificent job of dissipating the heat they receive so the thermostat and bypass system stay nicely in equilibrium. Accordingly, the temperature sensing system gauge never varies from central despite the raging heat soak accumulation in the block below. Ergo, everything seems rosy to the driver and yet inside the engine can be dense clouds of smoke rising to condense as bitumen.It didn't take me long to find that this seems to be a widely present phenomena in a a range of manufacturers' engines (but not all).Based on the evidence, faulty cooling system design and manufacture is key to the problem as it affected me. And I reckon like problems underpin the scourge of so called "sludge" affecting many engine types.In mine,a.   Coolant flow is severely restricted by inadequate porting through the head gasket. The sum of the areas of all of the gasket flow ports is less than the area of the pump output throat. Furthermore, the surface friction effect of all of the small holes through the gasket compared to that of the pump output throat, is about 4:1 against the flow. Hence the action of the pump is severely hampered and cavitation is inevitable (plenty of physical evidence of cavitation). and also;b.   the outflow ducting from the pump and its interface with the port into the block, have a number of significant sharp edge protrusions interfering with the path of the coolant flow. Cavitation and major bubble formation is thus further exacerbated.To make matters worse, the occurrence of bitumen is cumulative and cannot be removed by any amount of routine servicing or flushing without removal of the sump.The problem here is defective design. The sump drain plug is positioned well above the lowest point. Thus the sump cannot be properly drained. Interestingly, the oil; uptake draws right from the very bottom of the sump (witness marks on the bottom of the sump and careful measurements prove this to be the case. So when heated, the bitumen accumulation is circulated through the lubricating system.Mine failed because varnish from the bitumen set around the cam followers so that when I went to start it from cold, crunch clack clack clack whir whir and cam shafts were damaged, cam cogs, chain and guides were mangled.Sorry this is so long. There is plenty more, like with hindsight how to detect the onset and prevent failure occurring. I'd be happy to answer any questions you might have.By the way, on rebuild, I had the gasket calibrated to overcome the restriction problem and the surface friction effect: Also, I spent a little time smoothing the flow path for the coolant and I repositioned the sump drain and shaped the bottom so that every last drop can be drained at any reasonable vehicle angle. Bitumen will never again be a problem in my engine.I have also introduced a thermocouple permanently into the sump to monitor sump oil temperature. Oil temp now runs between 85 and 87 Degrees Celsius and peaks at 94 Degrees Celsius under heavy load climbing. Oil company representatives had previously told me that Toyota LandCruiser sump temperatures ran normally at 100 Degrees Celsius plus. Proof is in the pudding for me and I am very happy indeed with the results of my study and work.Kind regards,Roy Edgar in Canberra, Australia "</blockquote>

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