Mike02z

That is not how it works. The second number is the viscosity when the engine is at operating temperature. Running a 40 weight oil in a car designed to use a 20 weight oil will most likely give you problems. Not right away but a true 40 weight oil is too thick for the 4.6 IMO.

Running M1 5W-30 is fine because lab tests show that the Mobil 5W-30 is closer to a 20 weight at temperature. I'm not an oil expert but I did read a lot over at bobistheoilguy.com

Tylus

you'll be okay.

I personally would drain and put the correct oil in there. Just leave the Filter. The 5w20 will dilute down the 5w30 sufficiently that the motor won't know a difference.

Better safe than sorry IMO...just run the spec'd stuff.
x2

been using the 5w20 in my Fords for about 10 yrs now. From 100% stock motors to Supercharged 5.4 3v that I drove extremely hard.

never once had an issue or any noise. From Washington to Texas and now Hawaii.


Ford Engineers spec'd it for the CAFE requirements...yes. But the engines are also built with this oil in mind. A thicker oil isn't necessarily going to lubricate the same areas as well as the 20 wieght can/will.


They are the Engineers who have intimate knowledge of these motors...not us. I recommend you stick with the Experts. Heck, even Roush/Saleen say to use the 5w20 oil. I think they'd recommend a different viscosity if it was a problem.

Riptide

Actually Saleen and Roush do recommend a 30 viscosity oil. At least for their supercharged applications.

Regardless, it doesn't matter much. A 30 viscosity shears down to a 20 pretty quick. From what I've read the 20 doesn't shear as much.

Ford isn't the only company to recommend a 20.

Tylus

where do you see that?

I had a RoushCharger and asked them specifically. I was told to run the 5w20 and nothing else by the Roush Tech department

Riptide

I called one of the two (can't recall which) and was told a 30. I can't remember where but I think I found it on both websites. Was a while back when I looked though.

onederful100

Saleen does recommend 5w30 on SC applications.

onederful100

gt500's take 5w50

Nuke

Bottom line: 5W30 won't hurt, especially for one oil change, but if it bothers you, spend the few bucks and change it out.

PennState

yeah you should be fine..