best oil weight for 5.4L engine

I have a 99 Expedition (just acquired) which tows trailers and equipment 80% of the time. It has the 5.4 Liter engine.
We operate in hilly terrain, and the year-round climate is never lower
than 55F nor higher than 85F.
Looking for oil weight recommendations. It has 5-30 in it now. If thats fine, I will keep it, but if something else is recommended, let me know
thanks
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On 21 Oct 2005 13:28:14 -0700, "Joe"

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.
Lugnut
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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.
HTH

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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 http://mail.xpog.com/mailman/listinfo/expedition .
Regards,
Ed White
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