I recently bought 5L engine oil  from a reputable retailer , this being  5W-20 type, which their computer flagged up as specific for the Reg No. of my Focus Mk 2 2010 1.6L Duratec 16v(Sigma) engine. But as I was pouring it in, I thought it much less viscous so checked it - unfortunately after filling - against my Owner's Handbook and a VM workshop manual. THe Handbook was clear - the oil had to meet Ford Specification  WSS-M2C913C of a 5W-30 oil: But the 2012 Workshop Manual gave both the same  5W-30 specification AND a 5W-20 spec of WSS-M2C948-B,  specific to my VIN number. A further check of another 2022 VM Ford Workshop manual, not specific to my VIM but to the type of car and engine gave the Ford Spec of WSS-M2C912-A1 for a 5W-30 oil. The thing is I'm wanting the retailer to pay for an oll change using the 5W-30 oil , but I have to prove that they sold me the wrong oil. So any ideas of  which department in Ford I should contact for a definitive answer that will stand up in court if necessary?

The handbook is 15 years out of date.  The electronic system is correct.

Thanks Tom, that seems to make sense. So the most recent spec I currently have  is from the 2022 manual, which states WSS-M2C912-A1  for  5W-30. Otherwise I guess I can get a print-out from the local Ford Dealer using the latest software manual.

Specification WSS-M2C912-A1 originates from the 1990's and was replaced by the WSS-M2C913-A specification in 2004. This is just an error in the Etis system. 

The WSS-M2C913-A specification was replaced by --> WSS-M2C913-B --> WSS-M2C913-C and eventually by WSS-M2C913-D in 2012.


The latest service information prescribes that for the 1.4 / 1.6 Duratec engine (including TI-VCT) both the WSS-M2C948-B and WSS-M2C913-D specifications can be used. The WSS-M2C948-B specification is the primary choice, and the WSS-M2C913-D specification can be used as an alternative.


The seller sold the correct type of oil for this engine type.


 

Thanks JW1982. While it would be a relief not to have to change the oil again, it worries me that there is such a difference in viscosity between the 5W-20 and 5W-30 -how can both be right?- and do you think that the age and mileage of the engine might be a factor favouring the thicker 5W-30? My mileage for the 2010 car is 104,500 mles. Also I tend to do long trips of 300 miles or so fairly regularly, which i understand might also be a factor? But if both are specified currently, I can't complain.  

Keep in mind that the viscosity is not the only thing that counts.

Both the WSS-M2C948-B 5W20 and WSS-M2C913-D 5W30 oil types have the same viscosity at cold temperatures. At a cold start they roughly offer the same protective oil film thickness. It is a higher operating temperatures that the WSS-M2C948-B 5W20 becomes less viscous as the WSS-M2C913-D 5W20 oil. 

The WSS-M2C948-B 5W20 oil may be thinner at operating temperature but is also a much more advanced engine oil. Its advanced chemistry offers better lubrication purposes and enhanced wear protection. It was specifically designed for relatively high power, small displacement turbocharged engines and after a few Years also became the recommended oil for many of the older naturally aspirated engines. 


As far as I see it the better lubrication purposes and enhanced wear protection of the WSS-M2C948-B 5W20 oil compensates for the lower viscosity.

Hi again JW1982. Well,  the plot thickens. I went into the main Ford Dealer today and got the attached up-to-date Ford Microcat EPC print-out, which specifies 5W-30 MSS-M2C913-C. Their customer services guy explained that after a time of preferring the 5W-20 oil, Ford have now reverted to a single specification for the 5W-30.  So I dunnow.... I tend to think that you are probably correct because you refer to MSS-M2C913-D, rather than C, and maybe the EPC catalogue needs updating. One thing is clear, that even Ford are unsettled on this issue and change their mind on a regular basis. Do you have a print out supporting your information that WSS-M2C948-B is the primary choice?

the thin stuff is only for emission control and fuel economy - engine longevity doesn't count in the world of emission testing for halfwit governments, emission regs and manufacturer sales

as they fit a half broken spring on the oil pressure relief valve and a thermostat that fails closed to overheat the car - I run 5 30 and wouldn't use the thin stuff - the other element of running 20w it is to get a quick start up on the designed to kill cam drive, that is the sole reason car's have the start stop insanity many lemmings love

 

So my conclusion from the discussion above is to use both the WSS-M2C948-B 5W20 and WSS-M2C913-D 5W30 oil types in a 50/50 combination - the idea being to get the best of both worlds. I've been running with that this winter and as far as I can tell without problems.