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Ideas on why Viscosity is climbing

Viscosity is climbing at 15,000 miles on the oil viscosity is at 16.9 no additives, soot is at .04 Sodium is at 7 potassium is at 5 and silicon at 6 no evidence of antifreeze so what's going on any ideas

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4 Answers

sludge? i've read that oil may thicken due to engine's low operating temp or bad crankcase ventilation. iirc you have a cummins isx and those are known to plug the crankcase filter. that's the best i've got...

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Thanks it is a Cummins ISX but the temp is fine never drops below 195 and the crank case filter was replace when the oil was changed.

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are you running delo by any chance? when i ran it my boron and viscosity would always climb over time. never had that problem with rotella but my n14 drank too much of it so now i'm trying delvac to see how it holds up.

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Jerzy I am running Rotella T 15W/40

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Are you using any products like Lucus Oil Stabilizer?

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No just oil and it doesn't matter what brand either

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Try another brand of oil next go around. I was getting the opposite problem, viscosity loss, using a Delo 5w40 synthetic. I switched to Schaeffer synthetic oil and the unexplained viscosity loss disappeared. Over the years, I have become convinced more than ever, that engines, even within the same brand, can be fickle about what oil they seem to prefer. Not that the oil or the engines are bad. It is akin to .22 rifles and ammunition. I can take two high quality rifles and feed them both a quality ammo and get one that shoots better than the other. If I change to another quality brand of ammo, the results reverse.

Try a different brand and see how it plays out on the oil sample next time.

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Cliff I've tried Mobil Delvac 1300 15W/40, I've tried Delo 15W/40 and I am now using Rotella T 15W/40 and waiting to get enough miles to check it

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Jerzy Zaleski you were close to the problem. I found my viscosity problem or I should say Blackstone Labs did. I sent 2 samples in 1 to Polaris Labs and 1 to Blackstone Labs they both flagged the high viscosity but Blackstone said it was due to higher than normal oil temp so I knew Cummins uses a Oil cooler thermostat so I changed out the thermostat and everything is back to normal and good. Thanks Everybody for your ideas

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Mel will be eternally grateful.
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