Recently, while doing PM of our Diesel engine (Make-Carlson, 6 cylinder engine), the lube oil was found deep black in color however,we changed the oil (Oil Total make, SAE40). It has run only approx 720 hours. Can some one suggest-should, I go for further investigations??

Hello GC Verma,

The sooth excaping from piston ring or blow-by is what makes the diesel oil black. And these are contaminants perhaps in the range of 3 microns which is far my estimate. I micron is 0.000039 millionts of an inch. Perhaps same size if you can get one piece of yeast. Our eyes can only see in the range of 40 microns in size. An average oil filter which you have in your diesel engine can remove solid particles in the range of 30 to 40 microns hence these soothe will escape your full flow oil filters. Should you want to improve your oil cleanliness you can adopt some oil by-pass filtration these are secondary filtrations besides the original oil filter you have. What is important is to specify the efficiency and beta rating of the secondary filters.

Hope this helps.

Rolly Angeles

GC Verma,

The accumulation of soot in many types of diesel engines is quite the norm, but there is such a thing as too much soot. Unfortunately, visual inspection is not an adequate method to determine how much soot is present. The most common method for soot determination is infrared spectroscopy. Most oil laboratories provide this test at a reasonable cost. It looks for an increase in the baseline attentuation of the IR absorbance of the sample, and correlates that to a soot level. Most engine designers can specify a maximum soot level (typically in percent wt/wt) and you can use this as a guideline to change your oil out. If you have a lot of engines, and would frequently need to check soot levels (such as fleet applications), instruments like the Wilks InfraCal soot meter are specific for just measuring soot. But if you are just trying to troubleshoot or occasionally check if you "black" oil is normal or has too much soot, I'd suggest a simple lab FTIR test.

Hope this helps.

Rich Wurzbach
MRG Power Labs

720 hrs. is a lot to expect from your oil unless it is of a superior quality like Lubrication Engineers brand. These hours are possible with an enhanced product but I wouldn't try that with a commercial grade oil and especially a "bid winner".What is your engine's OEM spec for oil changes? Are you using a highly accredited lab for analysis? Does your fuel have a higher than normal sulphur content? I would be glad to take this further at your request.monolec@suddenlink.net

I stand corrected, not used to ULSD so sulphur content doesn't factor in here.