Hi,
Roger3116,
I change the oil at around 3.00%. Since starting the analysis programme some years ago the highest reading has been 3.58% and the lowest at 2.90%
ExxonMobil had initially set a limit of 2.00%. But when Detroit lifted their limit from 1.5% to 3.00% when using CH4 mineral oils, the ExxonMobil limit was adjusted to 3.5%
The main criteria for change I use is distance - no more that 62000 miles - adjusted down by the TAN at/above 8, viscosity being outside ExxonMobil's limits, any dangerous contaminants and unusual wear metal movements etc.
At 62000 miles Delvac 1 is still suitable for use and it is probably only my conservatism and the service /inspection regime that I use that inhibited longer intervals at this stage
The amazing thing to me is that the viscosity has always been within limits. Our average has been 86, with the lowest 74 and the highest 90. The limits we use are, low 72 and high 119
The individual distances on my trucks discussed here is now between 510-550000 miles
On any new truck I purchase I will continue to use the Mann-Hummel "Spinner" and go to longer OC intervals using analysis on Delvac 1 CI. I will also install a self-greasing unit to enable adjustments to the service schedule
Regards