Will a sludged engine consume more oil?

[Dr. T]

When I recently switched from BMW's 5W-30 fake synthetic to PAO due to visual accumulation of sludge and varnish in the oil filler cap area, I noticed an increase in oil consumption, but also a cleaner engine. Now (after 4 oil changes) the consumption has ceased. Can it be that one can see a rise in oil consumption because the oil is "cleaning" the engine out eg. from neglect or conv. oil deposits before consumption stabilizes?

 

[MolaKule]

Most likely, the rings were "reduced" of deposits somewhat. Ring deposits do not allow the rings to flex and therefore, the sealing of the combustion chamber is reduced, allowing oil to get past the rings in "reverse" blowby, increasing oil consumption. I would highly recommend Neutra or Auto-RX to further clean the engine. WHile synthetics are good at continued cleaning, they cannot clean like a dedicated engine cleaner, which slowly removes sludge and carbon deposits.

 

[Dr. T]

I agree...seems like standard oils (even synth. PAO's) stay and keep the engine clean, but DO NOT really clean things once they're really mucked up....other than prolonged use and many changes later.... But, this past round I've used Delvac 1 which I found did a tremendous amount of cleaning....probably the best so far....the engine runs better, quieter and more powerfull with each tankfull....should I continue to use Delvac or can I switch back to standard M-1?

 

[TooSlick]

Dr T, The answer to your question is Yes.... It is very common to see increased oil consumption when a high mileage engine is first switched to synthetic. I'd recommend reducing the filter change interval by 50% for the first 10,000-15,000 miles after changing over. It's not a bad idea to do the first filter change after 2000-3000 miles, as it will tend to load up with sludge. This dirty oil provides a poor piston ring seal, so consumption can go up significantly while this cleaning is taking place. If you have a significant layer of sludge sitting in the oil pan, the oil level will also drop as this is loosened up and filtered out. Once the pre-existing sludge/varnish/carbon deposits have been removed, oil consumption should be lower than with the same SAE grade of petroleum oil. The reason for this is that full synthetics have much lower evaporation rates than Group I/II petroleum oils.

 

[Dr. T]

So does that mean it's a downward spiral with sludge. A little bit causes an increase in consumption followed by some more sludge, followed by increased consumption and more sludge and they cycle continues. Which then leads me to ask....does the continued sludge build up and consumption cause slow and continued engine damage? And if so, can be arrested and reversed?

 

[TooSlick]

Dr T, Delvac 1, 5w-40 is the best product Mobil makes ....It is more shear stable than their 0w-40 and has higher additive "treat" levels. I don't have any experience using it in a gas engine, so I'd suggest doing an oil analysis after 7500 miles to see how it's holding up. As for keeping the engine clean, I would try to keep the TBN at changeout > 6.0, as well as keep oxidation/nitration < 50% of their allowable limit. This will insure you have plenty of detergent/dispersant additives remaining and aren't creating new sludge/varnish deposits. BTW, it is the organic esters that do the cleaning, not the PAO's ....