Mobil is removing their DTE 797 and Teresstic GT 32 product lines and replacing it with DTE 732. They say that compatibility is not an issue. Anyone have thoughts or experience?

We have seen demulsibility issues on several turbine lube oil reservoirs recently that were using 797 and have been adding 732 for top-off. The turbines were originally fitted with coalesce technology for water removal which seems to be disarmed now. On all of these reservoirs where the demulsibility was lost we were able to remove and maintain water below saturation with Hy-Pro vacuum dehydrator. We do not claim that blending 797 and 732 is the problem but we have seen this loss of demulsibility on several systems that have a blend.

Mark;

When you said "they say that compatibility is not an issue", I assume you probably referred to what oil reps told you. Well, they might be right and they might be wrong. For your assurance, before you purchase new oil you should test your in-service oil and the new oil for compatibility by an independent commercial lab (we use Herguth Labs, which actually developed this method for ASTM, hence has wealth of experience with compatibility evaluation). The test method is ASTM D 7155. You can elect to do a full blown test method (which is kinda spendy) or you can request only Tier 1 part (visual observation and evaluation) plus any additional test(s) on a particular mixture(s) of your interest (e.g. foaming, water separability, etc.). Only testing that showed full compatibility may be your best bet that you will not experience any operational problems that may be caused by mixing incompatible oils.