Cummins ISX Viscosity issue

Just a guess, at 800k miles, your getting some loss at the rods and mains. Don’t think its the oil. Personal opinion, additives like Lucas are not worth the expense.

Some things you may want to consider.

Run a dyno on it, see what the CC pressure is.
Do an oil analysis on the existing oil.
When you do a full oil/ filter change, get about 6 oz of the fresh oil and split into samples, mark them as base line. Then do samples every 10k send both the base and the 10k sample. A good lab will know what tho do.

Last, if your really concerned, look into doing rods and mains, and run an overhead. Fresh oil/ filter start the analysis cycle over.

 

In my opinion, miles on an engine don't count, it's the hours put on.
Idling is a big contributor to engine wear, even with the rpms bumped up. And you're still not moving.

 

I have a real good suggestion - get a mechanical gauge and put it on the engine. The one on the dash unless it an older truck is electronic, not even electric and controlled by the ECM.

 

Delete

 

Question
Who is testing the oil samples?

If you are using Speedco you are not getting the best test.

Fuel dilution would lower viscosity. So how much diesel is present in the sample?

 

If it's simply the oil filter plugging I'd consider adding a bypass filter, but like another said a change in viscosity could be fuel dilution. I use Blackstone for my testing and highly recommend them.

 

Speedco no longer does Oil testing.

 

A solid suggestion. Easy to do as well.