I believe 5w30 is what is recommended for it. Under your
temperature conditions, I would use 10w30. It really should
not make much difference since the w part only comes into
play at low temps. You do not want to use a heavier weight
than recommended because modern engines are very dependant
on flow volume which can be restricted by high viscosity
oils. I won't recommend or criticize synthetic oils or dino
oil. In my personal vehicles, I have always and will
continue to use a name brand dino oil. I routinely get over
150K miles with no major engine problems other than
occasional seal or gasket leaks that need attention and
usually go over 200k before trading. I change oil and
filter at 5k intervals using either the manufacturer's
filter or a Purolator brand filter. There are other good
ones out there but I tend to stay with what experience leads
me to believe is working for me.
Factory recommendation is 5W20 for most operating conditons..... for your
climate 5W30 may be an option. Your owners manual should have a temperature
chart showing preferred viscosity for different temperature groups.
Originally the Ford recommendation for your 1999 Expedition was 5W30. Ford
issued a TSB recommending the use of 5W20 that meets Ford Specification
WSS-M2C153-H in many older engines (including yours). This was done
primarily to increase the corporate fuel economy (by around 0.6% on
average). Personally I'd just stick with the 5W30. I've argued both sides of
this issue, but after a lot of soul searching, I've gone back to 5W30 for
all my Fords (even when 5W20 was recommended). I've read a number of SAE
papers on the subject of 5W20 oil and all agree that 5W20 will not lead to
durability problems. The only negative paper was from GM and it indicated
that 5W20 provided slightly (and I mean slightly) less minimum bearing oil
film thickness than 5W30. I have a 2003 Expedition and Ford's recommendation
was 5W20. I noticed a slight knock at cold start-up. It sounded like piston
slap and was not serious, but it still bothered me. I tried Mobil 1 5W30 and
this eliminated the noise. Do I think using 5W20 oil instead of 5W30 will
measurably decrease the life of the engine - NO. Do I think that using 5W20
will measurably increase my fuel mileage - NO. So it comes down to a coin
flip. In my case 5W30 is winning at the moment.
You might like to hear the opinion of other Expedition owners by joining
the Expedition Owner's Mailing List. See
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