Agreed..... we have run large Cummins, cat and iveco engines in our equipment in a hot, dirty environment for years..... no engine failures, regular oil changes and rotella t 15/40 synthetic blend....
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I'm not sure you agree with Dozerboy, he is for extended drain intervals and stated that your concern over contaminants can be addressed in many ways.
Dirt getting into your oil is the result of poor air filtration. Judicious air filter maintenance is important. I've gone round and round with many that are against extended drains, yet blow out air filters daily, some even feel they don't need to replace them ever, just clean them. That said, there is nothing inherently wrong with properly cleaning an air filter when needed. The key words being "properly" and "needed". Many newer systems on off road equipment do an outstanding job and have much longer intervals and may never need cleaning. Others need cleaning or it would get expensive fast. In that case, proper cleaning(when filter restriction is indicated) is important, as well as proper inspection before reuse. Replacement intervals should also be specified based on filter condition after x amount of cleanings. If you can't inspect the main filter properly (blue light/dark room works well), just look at the safety filter, if it's getting dirt on it, your main filter needs to be replaced. If you don't have a safety filter (like most trucks), you shouldn't be cleaning the filter.
UOAs can show how well your air filter program is working. I had trouble with one guy always wanting to clean a feed truck filter (no safety), anytime he would, silicon would spike 30-50 times the level it would be if filter was never touched.
There is still a certain amount of dirt that ends up in the oil though. If you air filtration system is in good shape and the silicon levels start to increase before your oil deteriorates, you need better filtration. That doesn't always mean additional filtration, on a lot of stuff you can simply change the filter(s) as needed.
The "soot" you mention is also an issue, however it is the job of the oil to neutralize the acids formed due to soot, something that is also shown in a UOA as the TBN and/or TAN. The particulate portion will be filtered out, there is a separate spot on the UOA that lists the soot content.
Anecdotal evidence of "no oil related failures" means very little as the number of engine failures/accelerated wear related to the oil itself are limited. Too many people focus on changing the oil early and calling it a "cheap overhaul", yet they neglect coolant and air filter maintenance. Coolant is responsible for more than 2/3 of the engine related downtime in the heavy duty trucking industry. There are many oil related wear/failures that are due to coolant contamination, fuel contamination as well as dirt contamination from poor air filter maintenance. However you will have a hard time detecting contamination without a UOA, until it's too late.
Cheap overhaul is shortsighted, with proper extended drain intervals, the costs of oil changes at the intervals some suggest, can outweigh the cost of an overhaul over time. The cost portion means very little for a single car or truck, but on a larger fleet it adds up fast. I've added it up in my case and the savings on oil changes alone are 5 figures(and I use cheap Delo 400LE). I've never had an oil related failure either.
For HD wet sleeve diesels, coolant maintenance is far more important than oil, much less the brand of oil you choose.
A UOA is a tool, I'll use them to extend drains, evaluate filtration and detect contamination, but I tend to ignore wear metals unless they are significant. I'm not going to rebuild an engine just because the UOA says the wear is high. I have used them to find issues with air filtration, fuel systems and cooling systems though.
When I extend drains, I don't go for the max possible. I send in samples at certain intervals and go as far as possible on the first drain, whatever it ends up at I cut in half and just send a sample when the oil is changed, or one sample per year, whichever is shorter.