B&S Vanguard Synthetic 15w-50 oil

That's true. So are all the other oils on the list that Ford provided. But the fact that some don't meet the specs that CJ-4 did means that it isn't backward compatible.

It used to be that all you needed to know was the 'weight' and API cert in your owner's manual and anything with that cert or higher could be used in your engine. Not true anymore. Unless your engine manufacturer's blessing is on the container, you just don't know if it's OK or not. It may be (Rotella T-4) or it may not (Mobil Delvac).

Cpurvis- I agree, different world anymore..

I called Rotella today & spoke to a tech, he said the T4 formula has remained unchanged.. FWIW.

I think these oil companies really don't want us to know what is actually in the oils. Got a bottle of Kohler oil a while back, rear label said "meets or exceeds api sj" or something like that. The "exceeds" part is an open door to disaster for some motors that require the barrier lubrication of the older oils. Remember when oil was advertised with graphite in it, see some black stuff in the bottom of the jug even.

As we know, no mower engine maker produces their own oil, they sub it out to the best price for their specs.

So.....