5W-20 isn't too hard to find.  Personaly I don't like it and would use
5W-30.

Ford specifies 5W20 for slightly better fuel mileage. particularly on
short runs where the engine never fully warms up. BTW, I see 5W20 at
A-Z, A-A, or W-M, in several different brands, so it's not that hard to
find.

Most likely if you look in the owners manual, and sometimes even on
the dipstick, it will show alternative oil weights that can be used. I
think it would be very difficult to reject a warranty claim since they
used 5w30 and 10w30 in the same engines for years with no warranty
issues.

The reason they went to 5w20 was to squeeze another 0.1 mpg out of the
ratings.  In order to create a 5w20 oil that provided the same
protection as the "old" 5w30 and 10w30 oils they had to resort to the
use of some synthetic oil in the mix and do a lot of other
reformulating. And even after that the best they could say about the
new oil was that it didn't seem any worse.  I think you are far better
off using Mobil One 10w20 or 30 .

This question comes up regularly. It is not just Ford that recommends 5W20.
Honda and Toyota (some vehicles) do also. It is unlikely that using 5W30 oil
will invalidate your warranty. You would have to have an oil related failure
that Ford could prove was the result of using 5W30. However, if you go to
Ford and complain about lifter noise, or piston slap, or other engine
complaints, one of the first things they are likely to ask you is "Are you
using 5W20 Oil?" It should also be noted that the 5W20 oil is not a blanket
recommendation for all Ford engines. The 4.0L V-6 in Mustangs and Explorers
still requires 5W30 Oil. Here is some old verbiage on the subject from a
prior post (some of the info is getting old):

There have been a number of SAE papers by US and Japanese engineers on the
subject of 5W20 motor oil. Not one found that it caused durability problems.
GM engineers had one paper that found that the 5W20 oil had slightly reduced
bearing oil film thickness compared to 5W30, but the difference was trivial
and the paper was actually describing a measurement technique. Toyota and
Honda engineers have published papers that were positive about the use of
5W20. These papers claimed that their were no reliability problems
associated with the switch to 5W20 oil. Here is what Ford had to say when
the 5W20 was initially released (2001):

TSB 01-4-7

ISSUE:

Engine oil recommended for use in 2001 vehicles is SAE 5W-20 motor oil. This
oil has an improved formulation to improve fuel economy. This oil can also
be used to service some previous model year vehicles.

ACTION:

Use SAE 5W-20 engine oil at recommended oil change intervals for 2001
vehicles, with the exception of the following vehicles listed in the
"Exception 2001 Vehicles" chart. All 2001 vehicles other than those listed
in the "Exception 2001 Vehicles" chart are being filled with SAE 5W-20 motor
oil at the factory and should also be serviced with SAE 5W-20 oil.

Vehicle Application Listing Approved For SAE 5W-20 Motor Oil:
1995-2000 2.5L Contour/Mystique
1999-2001 2.5L Cougar 1996-2001 3.0L 4V Taurus/Sable
1999-2001 3.0L (Vulcan) Ranger (Flexible Fuel and Gas), Windstar,
Taurus/Sable (Flexible Fuel and Gas)
1996-1997 3.8L Thunderbird/Cougar
1996-2001 3.8L Mustang and 3.8L SPI Windstar
1997-2001 4.2L (SPI) F-150 (under 8500 GVW only), Econoline
1996-2001 4.6L 2V Mustang
1992-2001 4.6L Crown Victoria/Grand Marquis
1991-2001 4.6L Town Car
1994-1997 4.6L 2V Thunderbird/Cougar
1996-2001 4.6L 4V Mustang Cobra
1995-2001 4.6L Continental
1993-1998 4.6L 4V Mark VIII
1998-2001 5.4L 2V/4V Navigator
1997-2001 4.6L 2V Triton F-150/250 (under 8500 GVW only), Econoline,
Expedition
1997-2001 5.4L 2V F-150/250 (under 8500 GVW only), Expedition,
E-150/250/350, E-350 Chassis/RV/Cutaway
1997-2001 6.8L E-250/350, E-350 Chassis/RV/Cutaway
1999-2001 6.8L Super Duty F-Series 250 HD/350/450/550 Motorhome
2001 2.0L Zetec/2.0L SPI Focus
2001 2.0L Zetec/3.0L Escape
2001 2.0L SPI Escort
2000-2001 5.4L/6.8L Excursion
2000-2001 3.0L Lincoln LS
2001 2.0L Zetec Escort ZX2

NOTE: THE "EXCEPTION 2001 VEHICLES" SHOULD BE SERVICED WITH SAE 5W-30 MOTOR
OIL.

Exception 2001 Vehicles:
Engine Vehicle
2.5L   Ranger
3.3L   Villager
3.9L   Lincoln LS
4.0L   Ranger, Explorer/Mountaineer, Explorer Sport, and Explorer Sport Trac
5.0L   Explorer/Mountaineer
NOTE: IF VEHICLE IS NOT LISTED IN THIS APPLICATION, SAE 5W-30 OIL IS
RECOMMENDED. REFER TO TSB 99-8-16.

The following Q&A's were originally posted to the Mustang newsgroup several
years ago -

QUESTIONS AND ANSWERS REGARDING MOTOR OIL .... [ info on ATF deleted ]

Q. Why did Motorcraft release SAE 5W-20 motor oil?
A. It was the right thing to do for the consumer and for the environment. It
was one of Ford's first steps in improving the fuel economy of our SUVs by
25% by the 2005 calendar year. SAE 5W-20 improves fuel consumption by
approximately 0.6 percent. For the 2001 fleet, this amounts to reducing fuel
usage by more than 21 million gallons per year. This reduction in gasoline
consumption leads to a reduction in carbon dioxide emissions by 190,000
metric tons per year, which is equivalent to taking nearly 23,100 cars and
trucks off the road each year.

Q. Is there really a difference in quality between 5W-20 and 5W-30?
A. It is important to separate the differences in viscosity grade, and also
the differences in the performance standards set by the International
Lubricant Standardization and Approval Committee (ILSAC) and the
accompanying American Petroleum Institute (API) performance categories to
answer this question. First, SAE 5W-20 oils are slightly less viscous at
operating temperature
than SAE 5W-30 oils. This reduction in viscous drag contributes to reduced
friction in the engine and thus improved fuel economy for an SAE 5W-20.
Second, there are differences between the present ILSAC GF-2 standard (GF
stands for gasoline fueled) and the soon to be commercialized GF-3 standard.
The performance of a GF-3 oil will be significantly improved over a GF-2
oil. When Motorcraft released it's SAE 5W-20 formulation we wanted it to
perform at the GF-3 level; but the GF-3 spec had not been finalized, so we
'guesstimated' what GF-3 would look like. In so doing we doubled the length
of the standard dynamometer Sequence IIIE test (which duplicates high
temperature trailer towing) which increases wear protection and reduces oil
thickening. While GF-3 also improves on the standard GF-2 Sequence IIIE
test, it went nowhere near as far as Ford did. This provides Motorcraft SAE
5W-20 with a significant increase over 'standard' GF-3 oils, which most SAE
5W-30 oils will meet. Taking all this into account, the Motorcraft SAE 5W-20
will be a significant improvement over most SAE 5W-30 oils.

Q. Does the difference in price between Motorcraft SAE 5W-20 and SAE 5W-30
really reflect a better oil?
A. Yes. The better base oils, and increased additives such as friction
modifiers and anti-oxidants used to formulate for the performance levels in
the SAE 5W-20 do cost more, but reflect the significant increase in
performance.

Q. What Ford and Lincoln/Mercury vehicles use SAE 5W-20 oil?
A. Approximately 80% of 2001 models should be serviced with SAE 5W-20 oils.
By 2003 model year all Ford and Lincoln Mercury vehicles will be filled with
SAE 5W-20 at the factory. But there are a significant number of older
vehicles, some as old as 1991 models where Ford now recommends servicing
with SAE 5W-20. Refer to the chart listed in Technical Service Bulletin
Article No. 01-4-7 for details of which older models should use SAE 5W-20
and for the 2001 'exception' models which should continue to use SAE 5W-30.

Q. What happens if someone uses SAE 5W-20 in older vehicles?
A. As stated before some older vehicles have been approved for SAE 5W-20.
However, there are many older vehicles not covered by TSB 01-4-7, and Ford
is presently testing these to determine whether durability and performance
would be compromised if SAE 5W-20 was used. Until this testing is
successfully completed (and a TSB is published to this effect), it is not
recommended using SAE 5W-20 in an older model unless specifically mentioned
in TSB 01-4-7.

Q. Is Motorcraft the only brand for SAE 5W-20 motor oil?
A. No. Although SAE 5W-20 is not yet a popular viscosity grade, major
marketers including Pennzoil, Quaker State, Valvoline, Exxon and others have
either already begun marketing an SAE 5W-20 or have plans to do so.
Customers should find this viscosity grade increasingly available in coming
months, including at some retail outlets.

Q. Will SAE 5W-20 provide longer oil change intervals?
A. At the present time Ford recommends no change to the existing drain
interval for SAE 5W-20. However, Ford is investigating allowing longer drain
intervals since the performance level of Motorcraft SAE 5W-20 is
significantly better than today's GF-2 oils.

Q. Why does Wal-Mart have Motorcraft SAE 5W-20 so much cheaper than dealers
can now buy it?
A. Oil and Filter change is the number one Do-It-Yourself repair. Many Ford
Motor Company customers are avid Do-It-Yourselfers. Some may purchase
required products from our franchised dealerships, however, most prefer to
purchase products available at mass merchandisers. If our product is not
available they will buy other brands available at these
retailers. Ford Motor Company has an obligation to the EPA to ensure all of
our customers have access to this new oil and Wal-Mart is one of several
retailers carrying Motorcraft products. Wal-Mart bought several truckloads
of Motorcraft SAE 5W-20 at the original introductory price. These original
quantities are still available at Wal-Mart. As Wal-Mart re-orders Motorcraft
SAE 5W-20 in the future they will purchase it at the increased price.

[ ATF Info Deleted ]

---------------------------

I used nothing but 5W20 Oil in my 2001 Mustang as long as I owned it, and in
my 2003 Expedition for the first 85,000 miles. I never had any oil related
problems for either vehicle. However in the case of the Expedition, I did
have what I considered to be minor piston slap on cold mornings. I changed
to 5W30 Mobil 1 at around 85,000 miles and it seemed that this reduced the
noise, but to be honest, the noise was infrequent and not particularly
noticeable, so I am not sure the 5W30 actually made any difference. Ford
specifies 5W20 Oil for my 2004 Thunderbird, but I decided to use 5W30 Mobil
1 instead. The Thunderbird (and Lincoln LS) use a version of a Jaguar V-8
and in England, 5W30 is listed as the preferred viscosity for most
conditions for this engine (5W20 is allowed even in the Jaguar Owners Guide
for many conditions).

Ed

No.  The manufacture used 5W20 in the engine when it was certified for CAFE,
thus must recommend owners use that grade.

mike

I recently saw 5W20 Pennzoil even at the local Pep Boys, and I'm in
Arizona, where the hot climate tends to favor thicker oils. OTOH I
haven't seen 0W20 anywhere.