How long should I run this oil?

[Falcon_LS]

Recently did an oil change on the Grand Marquis, and refilled with Liqui-Moly Top Tec 4200 5w30 (Group III basestock). The specifications this oil meets are impressive (ACEA A3/B4/C3-04, VW 50400/50700 (2004), MB-Sheet 229.51 and BMW LongLife-04), however there is one major issue bothering me.

I contacted the gentlemen I'm in touch with at Liqui-Moly, and have been told the TBN of this lubricant is 5.5 (turns out to be low SAPS). My previous service fill (Liqui-Moly Synthoil Energy 0W-40) had a TBN of 9.6. The previous fill was in service for 16,010 km (10,006 miles), but because I wasn't considering running it again, I never took a sample for a UOA.

Now the confusing bit is, depending on application, Top Tec 4200 5w30 can be in service for up to 50,000 km (31,250 miles). But with a TBN of 5.5 and 500 ppm sulphur levels in our gas, it would require a miracle to go that far.

So I was wondering what an acceptable drain interval would be for the current fill. I'm considering 10,000 km (6,250 miles), but am open to suggestions. At my next OCI, I think I'm going to go back to the 0W-40 or go with their Synthoil Longtime 0W-30 (also Group IV) that I ran in my '03 Grand Marquis. Thanks!

 

[tig1]

I did 10K OCI with my old 96 Merc GM. Engine stayed very clean and quite for 218K. Mostly M1 10-30. A couple of M1 5-30 OCs.

 

[Y_K]

With the TBN cut in half only an oil analysis could tell you with certainty for how long it could be run. As for base Grp difference, it does not matter much for the modular 8 - they are known to be very easy on oil. What most people are confused with when it comes to Grp 3+ is this notion of 'highly refined oil' or 'severely hydrocracked oil'.
Not only it is highly refined - it is *isomerised*. That's a quantum leap. I would hazard to say it will serve you well for 10k kilometers easily even with the slightly elevated sulphur in your fuel.