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This message has been edited. Last edited by: tribology.services,

Generally engine oils and hydraulic oils are formulated using different additives. For example, engine oils have high detergents/dispersants (shown by high Ca or high Mg) and antiwear packages (high Zn and P). Hydraulic oils on the other hand do not have detergents - mainly antioxidant and antiwear (can be zinc based or zinc free. Perhaps there is enough hydraulic oil getting into the engine oil to dilute some of the detergent package. By Knowing typcially how much of each additive the engine oil contains, the dilution may be worked out by the reduction in add pack eg Ca goes down. Also knowing the KV of the engine oil and the KV of the hydraulic oil, you can work out the dilution factor. Compare the KV dilution to the add pack dilution for some confirmation.

Largely agree with Rene.
However a lot of mobile equipment use SAE 10W engine oil so additive variation is not that big(significant) in these cases.Also CAT TO4(used in hydraulics and transmissions) can look similar to engine oil additives.
In these cases drop in viscosity is the most important factor as engine oil additive levels and TBN will be maintained to a large degree with the above type of contamination.
Use flash(Seta flash , quick cheap test) or other test(FTIR) for fuel contamination

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This message has been edited. Last edited by: tribology.services,

tribology-services,
These message boards were originally set up for non commercial purposes ie individuals looking for help and assistance, or providing helpfull information and advice. Opportunities for people to share and potentially pick up some business by assisting those in need of assistance. We don't often see business's admitting they need help to understand and provide the service they are charging thier customers for.
I'd suggest you need help based on your questions and recommend you hire a consultant to address the issue.
Regards.......

appologies, the posts were genuinely intended as legitimate questions from a "lay man" - as the finance manager, and share-holder, I have a keen interest in this. Not being a specalist, I like to get a broad appreciatation of other expert opinions around the world, and yes, if we are telling our customers the right thing. Perhaps I am niave in sharing of information, I have clearly mis-understood the nature of the forum.

Accordingly I have removed the questions.

Regards