In 2018, Ford quietly updated the 5W50 oil spec from 931C to 931D. I was on the FCSD website yesterday and it caught my attention that there are two 5W50 part numbers now - one for 931C and one for 931D. So, I wondered, what's the magic all about?
It's been my habit to actually purchase Ford's published specs for the fluids we use in our cars. So, I coughed up $35 and got the new spec. It is, in some ways, quite different than the 931C spec, and in other ways, not different at all.
The biggest difference is that it's got a new test - "LSPI". That's "Low Speed Pre-Ignition" and it's part of the API test for API SN Plus. LSPI is essentially knock caused by debris in the combustion chamber. Direct injected turbo engines like the Ecoboost are the most vulnerable, although there don't seem to have been any problems so far. Port injected NA engines like the Coyote and the Voodoo don't suffer from it at all.
I think it's safe to say that if you've got a Ford GT, a Raptor or a new GT500, then 931D is coming soon to an Owner's Manual near you. That is, if it's not there already. I bought a 2018 Explorer Sport with the 3.5 liter Ecoboost last fall, and the Owner's Manual calls for the corresponding LSPI updated 5W30 oil.
In terms of other differences, technically it's pretty much a wash. Some deposit specs are tighter but that's about it. The changes seem to have been aimed at making the 931D spec a closer copy of API SN Plus. The biggest difference between API specs and 931D is phosphorus, which is not controlled for a 5W50 under API but it has to be 800PPM or less to meet Ford's spec. The bottom line is that if your owner's manual calls for 931B or C, you can run D without any concerns. Where it matters is if you've got an engine that calls for D, then be careful to use it.
It's been my habit to actually purchase Ford's published specs for the fluids we use in our cars. So, I coughed up $35 and got the new spec. It is, in some ways, quite different than the 931C spec, and in other ways, not different at all.
The biggest difference is that it's got a new test - "LSPI". That's "Low Speed Pre-Ignition" and it's part of the API test for API SN Plus. LSPI is essentially knock caused by debris in the combustion chamber. Direct injected turbo engines like the Ecoboost are the most vulnerable, although there don't seem to have been any problems so far. Port injected NA engines like the Coyote and the Voodoo don't suffer from it at all.
I think it's safe to say that if you've got a Ford GT, a Raptor or a new GT500, then 931D is coming soon to an Owner's Manual near you. That is, if it's not there already. I bought a 2018 Explorer Sport with the 3.5 liter Ecoboost last fall, and the Owner's Manual calls for the corresponding LSPI updated 5W30 oil.
In terms of other differences, technically it's pretty much a wash. Some deposit specs are tighter but that's about it. The changes seem to have been aimed at making the 931D spec a closer copy of API SN Plus. The biggest difference between API specs and 931D is phosphorus, which is not controlled for a 5W50 under API but it has to be 800PPM or less to meet Ford's spec. The bottom line is that if your owner's manual calls for 931B or C, you can run D without any concerns. Where it matters is if you've got an engine that calls for D, then be careful to use it.
Last edited:
