Ok, but if it was harmful, why make the recommendation at all. It gets them
no CAFE credits if you switch your old car to 5W20. And they do not make a
blanket recommendation. 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
casued durability problems. GM engineers had one paper that found that the
5W20 oil had slightly reduce bearing oil film thickness than 5W30, but the
difference was trivial and the paper was actually describing the measurement
technique. Toyota and Honda engineers haev both published papers that were
positive about the use of 5W20 and both papers calimed that their were no
reliability problems. Here is some old verbage released by Ford at the time
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 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 ]

What would make it more fuel efficient, besides reduced friction? And isn't
reduced friction good for the engine? Not to mention that with reduced
friction, the engine is cooler?

Sounds like a win to me.

Jeff