what oil should i use..what's best?

15w50 is probably way too thick. These motors have very tight tolerances. 5w30 is recommended for my 99 motor, and it is my understanding that for the 96-98 is 10w30. Maybe that is what is holding you back in the other thread

There's very little reason to run a 50 weight oil. Stick with a quality 5w/10w-30 weight. More importantly, keep a close eye on the oil level...

I would go with Royal Purple 5w-20 or 5w-30!!! That or Mobil 1!!

That is a bit much. The '03 and '04 Cobras call for 0/20 or 5/20 and if I remember correctly my '99 used 5/30. I ues Mobil 1 5/20. 15/50 is pretty 'thick' at start-up and only gets 'thicker' as it warms-up.

I think that you are asking for problems because it doesn't flow too well when cold or hot for our fairly tight-tolerance engines. I know that there are a few oil experts on this site, maybe they could inform you better.

5W30 is all you need.

5W = The 5 represents the viscosity of the oil when cold, hence the "W" after the number which represents "Winter".

Depending on where you live a 5W may be overkill. I run a 10W in all my cars here in Alabama because we very rarely see temps anywhere near freezing so having an oil that thin is not necessary.

U.M.

bowser1985 said:

going with 10w30 mobil 1 thanks

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Good all around choice.

U.M.

Never run the 5 weight oil. Its the fastest way to kill your engine. 5-20 is only put in to get a slight increase in MPG.

TheDukeOfEarl said:

Never run the 5 weight oil. Its the fastest way to kill your engine. 5-20 is only put in to get a slight increase in MPG.

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I'm not sure where you heard that a "5" weight oil will "kill your engine." Did you mean to say "50" weight? I would agree that using a 50 weight oil is probably too heavy for most applications.

You are correct that Ford switched from the 30 weight spec to the 20 weight oil strictly for CAFE (ie - fuel economy) purposes.

For the original poster (a little more info):

There are a small number of applications (perhaps 24 hour Lemans roadrace type action?) where a relatively "thick" 40 weight or 50 weight oil could be favorable. But, for the vast majority of folks out there, a quality 20 weight or 30 weight will do the job just fine for normal street/strip purposes. IMHO, running a 40, 50, or 60 weight engine oil is "too thick" and could possibly contribute to engine problems.

As Uncle Meat pointed out, the "W" designator in "0w-xx, 5w-xx, or 10w-xx" oils simply denotes that the oil is a multigrade oil. And yes, the "w" stands for "winter."

Think of it like this, a 0W-20 will "flow" better at cold tempeartures than a 5w-20 oil and the 5w-20 oil will flow better than a 10w-20 weight oil.

The same logic can be applied to 30 weight, 40 weight, or 50 weight oils.
ie - 0w-30 pours easier than 5w-30 and 5w-30 pours easier than 10w-30 at COLD temperatures.

If you live in a cool/cold climate, it's pretty common to run a 5w-xx or even a 0w-xx weight oil nowadays.

For a more in-depth explanation of how multigrade oils are classified, Google for some more information or read this quick explanation over on Wiki:

Motor oil - Wikipedia, the free encyclopedia

Now that you know what kind of oil to select, you have to decide what brand you want to choose! Again, it's more important to keep a close eye on the oil level on a semi-regular basis in order to avoid running your engine low on oil. Iit's happened to more than one cobra owner in the past and has resulted in destroyed engine bearings and a rebuild.

G'luck.

My info comes from a ford engineer that was part of the 4.6 testing. His comments were that he would never run 5W20 oil in any mod motor. 5W30 or 10W40 is what he would recomend.

I used motorcraft synthetic 5w20 in my first engine and at 10,000km it spun a bearing. I have been using castrol syntec 5w50 since and 36,000km later no issues. I have missed gears and over revved with no issues. I believe that the oil is to thank for that. I mean believe what you want about the tight clearences, but when have you heard of an mildly modded engine with 5w50 blowing? It's usually a car with 0w20 or 5w20.