01 Mustang GT 5W-20 Oil Requirement

Seraphitia102 · Dec 16, 2004

The user's manual says that it recommends 5w-20 oil for use in the 4.6L engine. Now I hear everyone on these forums saying that the 5w-20 requirement was for CAFE, or to increase gas mileage.

So my question is, do you know the advantages of using 5w-30 mobil 1 instead of 5w-20?

WRXracer · Dec 16, 2004

an advantage would be that their are a lot more oils made in the 5 30..

03redfiregt · Dec 16, 2004

And mobile 1 is a full sythetic. Thats what i use, because i wanted a full sythetic. and i think 5-20 is too thin. And i still get 21mpg in the city and 27mpg on the highway.

Seraphitia102 · Dec 16, 2004

so thicker oil results in better protection?

Seraphitia102 · Dec 17, 2004

if Ford recommends 5w-20, why do you guys put something else in regarding to grade of oil? heck I even put in 5w-30 myself, but that's when I thought Ford was still recommending 5w-30 since my friend's 00' Mustang recommends that.

bdcardinal · Dec 17, 2004

the only reason ford recommends 5w20 is for CAFE. i have had dealers try to tell me that its for internal clearance differences and that is a load of crap. Mobil 1 does make a fully synthetic oil that meets ford's requirement for 5w20, i believe they call it a 0w30. however i just get a 6pack of Mobil 1 5w30 for $23 at costco, which is less than a mile from my house.

Jesus · Dec 17, 2004

5-30 is fine to use. From what I have found on these boards and been told by a reputable tuner nothing has changed as far as the internal tolerances of the engine from the time Ford recomended 5-30. The 5-20 recomendation is trictly due to emissions stuff.

StangPro · Dec 17, 2004

The 5-20 requirement was caused by trying ot meet emissions and keep mileage up for CAFE. The oil is has problems though and some speculate can shorten engine life. Ford doesn't care though as the car will be out of warranty anyways.

Darkhorse845 · Dec 17, 2004

Seraphitia102 said:
so thicker oil results in better protection?

Yes.There would be nothing wrong with useing Mobil 1 5W30 though!

prsrizdgt · Dec 17, 2004

Seraphitia102 said:
so thicker oil results in better protection?

To an extent, but you will hit a point of diminishing returns. At cold start-up, where you really want immediate lubrication, the 5w-20 will flow about the same as the 5w-30 (that is the "5w" rating). As the engine warms, the 5w-30 will maintain a higher viscosity because in my opinion you haven't hit that "dimishing return" point yet. You won't see very many people running a 40 or 50 weight oil because the viscosity is so high that the cool engine flow characteristics suffer. It is my understanding that something like a 5w-50 is not practical because the added improvers neccesary to achieve this viscosity spread will shorten the life of the oil a good deal. Remember also that flow and pressure affect each other. If you had a manual pressure gauge on a car with 5w-20, it would have noticably lower oil pressure than the 5w-30. I don't really want lower oil pressure at 6000rpms.
I am not an expert or anything, this is just what I have read.

The one I can't figure out is why Cam manufacturers are so against using a synthetic during break-in when you want to minimize friction......I don't think its the same principle as breaking in rings is it? Maybe I am wrong, and you need a certain amount of friction....

Seraphitia102 · Dec 17, 2004

Thanks for all your help guys. I'm sticking with 5W-30.

prsrizdgt said:
To an extent, but you will hit a point of diminishing returns. At cold start-up, where you really want immediate lubrication, the 5w-20 will flow about the same as the 5w-30 (that is the "5w" rating). As the engine warms, the 5w-30 will maintain a higher viscosity because in my opinion you haven't hit that "dimishing return" point yet. You won't see very many people running a 40 or 50 weight oil because the viscosity is so high that the cool engine flow characteristics suffer. It is my understanding that something like a 5w-50 is not practical because the added improvers neccesary to achieve this viscosity spread will shorten the life of the oil a good deal. Remember also that flow and pressure affect each other. If you had a manual pressure gauge on a car with 5w-20, it would have noticably lower oil pressure than the 5w-30. I don't really want lower oil pressure at 6000rpms.
I am not an expert or anything, this is just what I have read.

The one I can't figure out is why Cam manufacturers are so against using a synthetic during break-in when you want to minimize friction......I don't think its the same principle as breaking in rings is it? Maybe I am wrong, and you need a certain amount of friction....

What is a "diminishing return?" by the way?

prsrizdgt · Dec 18, 2004

Seraphitia102 said:
Thanks for all your help guys. I'm sticking with 5W-30.

What is a "diminishing return?" by the way?

If her juices evacuate the friction points, it will get painful. At that point I promise you your pleasure return will diminish.

Black2001GT · Dec 18, 2004

I use Mobile 1 0W-20 full synthetic.

01MustangGT · Dec 18, 2004

the best for over 50,000 miles is 10W30.
i use either Castro GTX which is used in John Force Mustang or Mobil1 10W30

SKH · Dec 18, 2004

I use Mobil 1 0W20 but can see no problem using the 5W30. In warmer climates than Mn. I would be using the 5W30

smontgo · Dec 18, 2004

If you check some of the oil boards where people post UOA's (used oil analysis) you will see that in many cases the 20wt oils are posting better wear numbers than 30wt oils. I have been a diehard 5W30 M1 user but during this winter I'm trying 0W20 M1 to see how it does. Once it warms up again and I head back to the track the 5W30 will be put back in.
www.bobistheoilguy.com
-way more information than you'll ever need.

Seraphitia102 · Dec 18, 2004

01MustangGT said:
the best for over 50,000 miles is 10W30.
i use either Castro GTX which is used in John Force Mustang or Mobil1 10W30

How come it's better to use 10W-30 after the car hits 50,000 miles?

mity2 · Dec 18, 2004

03redfiregt said:
And mobile 1 is a full sythetic. Thats what i use, because i wanted a full sythetic. and i think 5-20 is too thin. And i still get 21mpg in the city and 27mpg on the highway.

It is too thin in my opinion. I don't think its bad choice, If you drive car through winter, but if Not(only drive summer only), just let it drink some 5W-30 Mobil1!

mity2 · Dec 18, 2004

Seraphitia102 said:
How come it's better to use 10W-30 after the car hits 50,000 miles?

Thicker oil. After motor piles up some milege, space between metal(like Crank journal to main bearing spacing for instance) gets bit wider as metal wear. So idea is that thicker oil can stick to these wider space better then thinner oil.

01 Mustang GT 5W-20 Oil Requirement

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