[tmhutch]

Hopefully putting this info its own thread will help clear up the confusion caused by the oil viscosity change in 2001.

The bottom line is, we really shouldn’t be running 5w20. The switch from 5w30 in 1999 to 5w20 in 2001 (on identical engines) had nothing to do with wear or reliability issues and everything to do with Ford saving a few bucks by meeting CAFE standards. At the time Ford was fined $5.50 for every 1/10th of a MPG under the target average of 27.5 MPG for every vehicle manufactured. To help meet the target Ford changed from 5w30 to 5w20 and was able to improve mileage by 1/16th of a MPG and meet their goals.

Here are a few quotes from people with first hand experience:


Mike Riley, Product Design Engineer with Ford Motor Company:

Quote:
"Moving to 5w20 was driven by ... CAFE requirements. The company believes the switch to lighter viscosity 5w20 oils will reduce carbon dioxide emissions by 190,000 metric tons a year and reduce US fuel consumption by over 21,000,000 gallons a year."


While most people understand the main function of oil is to protect the engine, Ford's only concern in that respect is that a stock engine survives the warranty period.



I especially appreciate Scott Whiteheads insight on this topic. He worked for Ford testing different oils in modular engines and here is what he had to say:

Scott Whitehead - Engine Development Systems Engineer, Ford Motor Company:

Quote:
"I've seen the dyno testing. I've probably looked at several hundred engines disassembled and spread out on inspection tables. And I've been involved in testing to resolve issues where varying the oil viscosity was part of the test. Please do not put 5w-20 or less into a mod motor. Please. This is especially true in 4v motors. 5W-30 is probably a good oil for the street with mixed temperatures."


Ford Racing Group apparently feels the same way:

FRPP Group:

Quote:
"DO NOT go back to using 5w-20"



Some of the best data from the modular community has come from Nick McKinney:

Quote:
"I have said it a few times now, heavier oil has better protection especially in the cam bores. ---I get 2-3 sets of modular heads a week through here, and any lay person just from looking would pick the 500,000 mile cores run on 15W-40 diesel spec all their lives over the typical Mustang head run 50,000 miles on the light stuff"


Fleets typically run their vehicles 250,000 to 500,000 miles! I've heard Nicks experience echoed several times by fleet managers. They wouldn’t run a 5w-20 oil for one minute.

There have been concerns over bearing tolerances and lash adjuster pump up with heavier weight oils but these are largely overblown. Bearings tolerances haven’t changed since the 60's and much of the small difference found at the crank bearings is because of the aluminum blocks different expansion rate. A reality check for those concerned is the fact that while the 01+ modulars were spec'd to 5w-20 oil, the exact same engine pre 01 was spec'd with 5W-30. When Shelby modifies the 4.6's he covers the 5w-20 spec sticker under the hood with a 5w-30 spec sticker. In Australia all their modulars are spec'd for 5w-30 and higher because they have no CAFE standards. And the GT500/GT's with the exact same bearing clearances are spec'd for 5w-50w oil.

Bottom line, the thicker the oil, the better the protection. Just make sure you're running the proper weight if you live in colder environments.

As far as which brand oil to choose, there are lighter weight oils made from better stock that also contain anti-wear additives that provide superior protection (Red Line, Amsoil Etc.) but these additives often preclude the oil from meeting CAFE standards, not that I care about that for my limited use hot rod.

In the end I think it is best to stick with the wisdom and experience of a Ford engine development engineer who spent hours blowing up DOHC engines using different oil viscosities. So for now, 5w-30 Red Line, Amsoil, Mobil 1 and any straight 30 weight or diesel spec oil get my vote.

Todd