Hello everyone; I will be changing the oil in my '05 GT again soon, and I am currently using Mobile 1 sythetic, 5w-20, the same as the owners manual recommends. However, I work with a gentleman that is a professional race car builder/driver (he doesn't get paid big bucks for doing this, but he has wealthy sponsors that pays the bill for him to build and race) and he told me that in every engine, where the factory recommends 5w-20, he uses synthetic 10w-30. He said that he gets better performance out of an engine, when he uses synthetic 10w-30, when the manufacturer recommends 5w-20. He said that when the factory recommends an oil that is as thin as 5w-20, you can use synthetic 10w-30 (not conventional 10w-30), because synthetic oils are so thin. Since he is not that familiar with the new Mustang, he didn't recommend what I SHOULD use, he was only saying that he uses synthetic 10w-30, in all engines where the factory recommends 5w-20, because it gives the engine a little better performance, in terms of horse power, or whatever. Does anyone know anything about this?
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2005 Premium GT, Redfire, 5-speed, dark charcoal leather interior, IUP, 500 watt Shaker stereo, 17" Bullit wheels, rear spoiler
Engine upgrades: Alternative Auto Performance tune, C & L cold air induction kit
Exterior and Interior upgrades: Flameball Raspberry hair design shifter knob, custom 'GT' floor mats, Steeta satin finished door locks, temperature controls and voltage plug, Street Scene rear quarter louves, and Astra Hammond rear window louvers
Yea never change oil weight use what the dealer recommends, but oil brand is up to preference. I changed from Mobil Syn to royal purple at like 75K and really like it. I want to go with Amsoil but really do not like the price.
Given my recent experience with oil problems (not my own, by the way) I can tell you that if you have a problem, the first question they're going to ask (and they did) is what oil are you using.
Second, oil weight is a function of viscosity. Viscosity measures a fluid's (any fluid's) lubrication qualities. All fluids have a viscosity. Olive oil, very low, grease, very high. So when a specific viscosity is specified, any lubricant that meets that requirement is acceptable. Now, peanut butter oil may have the same viscosity as 5w-20, but that doesn't mean it will stand up to the same temperature and abuse an engine puts out. So we use oils specifically designed for engines. They are designed to maintain viscosity irregardless of engine temperature, etc. Now, you may be able to adjust the viscosity, but in my experience, the engineers picked that specific viscosity for a reason, and it's best not to deviate from that. Now, having said that, I know up north we used to change viscosities based on the temperature. Oil tends to get thicker as it gets cold. But, the owner's manual still specified what to use.
I would stick with 5w-20.
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'05 Sonic Blue GT w/ '07 V8 engine, 5-sp, IUP, Beige leather interior, nothing else -
just the way I wanted it. (1 of 113)
OK, so I've added a few things to it. Check my Profile - too many to list here.
And I would suggest going back to the synthetic blend Ford puts in these engines. The variable valve timing is controlled by viscosity/weight. Using a full synthetic is going to cause a timing issue. Many leaders of the industry that deal with the S197's clearly state that owners should stay with the motor craft blend and not run full synthetic. I tried mobile 1 super syn for one oil change and switched back and did notice the difference.
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2006 GT Premium 18"
JLT 2 CAI, SCT 2 Evo tune, LT Kooks headers, X-pipe, High-flow Cats, Borla S-type, Hurst Short Throw, Sequential, Tint, and 12" Stripes.
"All of us who are human beings are in the image of God. But to be in his likeness belongs only to those who by great love have attached their freedom to God."
I run 10-30w AMS Oil. No Problems whatsoever.
My opinion is the reason that ford recommends the lighter weight is for mileage.
I will trade off for the protection.
Hello everyone; I will be changing the oil in my '05 GT again soon, and I am currently using Mobile 1 sythetic, 5w-20, the same as the owners manual recommends. However, I work with a gentleman that is a professional race car builder/driver (he doesn't get paid big bucks for doing this, but he has wealthy sponsors that pays the bill for him to build and race) and he told me that in every engine, where the factory recommends 5w-20, he uses synthetic 10w-30. He said that he gets better performance out of an engine, when he uses synthetic 10w-30, when the manufacturer recommends 5w-20. He said that when the factory recommends an oil that is as thin as 5w-20, you can use synthetic 10w-30 (not conventional 10w-30), because synthetic oils are so thin. Since he is not that familiar with the new Mustang, he didn't recommend what I SHOULD use, he was only saying that he uses synthetic 10w-30, in all engines where the factory recommends 5w-20, because it gives the engine a little better performance, in terms of horse power, or whatever. Does anyone know anything about this?
I agree i did read something about the use of 10w 30 syn, has better
adhesion to the engines parts, under colds starts, and that it offers a higher degree of protection due to heat. and cylinder pressure.
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DSS 331 stroker, AFR 185 heads, Performer rpm 2 intake, Accufab 75 mm race TB, 30lb injectors, 80 mm Pro-M mass air, Extreme energy cam 266.
Anderson ford power pipe the big one, Ford motor sport shorty headers, Bassani x pipe custom cat back with flows, World class T5, center force duel friction clutch.
i am a ford certified technician i come across so many issues on the new 3 valve engines when using other weight oil that the one recommended. i 100% recommend sticking to 5w-20. those engines have very tight clearences between bearings that is why they recommend that weight oil. it is thin oil on start ups and when cold. then gets thicker when hot. even if you go past your oil change due mileage or date you can damage your engine...... i have seen it happen...always stick to synthetic for better protection.. as for brand they all have to meet the same requirements.. mobil 1 is said to be good...
Oil viscosity is in a constant flux due to heat.
Yes it would even be in a constant flux in different parts of the motor
due to heat differences in those parts.
If bearing clearances were the factor then anywhere in that engine
would be able to handle the heaviest weight recommended by the manufacture.
The only time the oil would be at the thinest viscosity would be when it is at it's coldest. That would ONLY be right at startup and not long after that.
Now the Heaviest viscosity would be at the hottest extreme and part in the motor. Where would that be??? The Rings and Valves Not the bearings.
So this being true the place where the flow would be most critcle would be there.
Are Valves pressure lubed? NO.
Are rings pressure lubed? YES.
So the Rings are the primary concern.
Oil viscosity ratings are set by SAE at 0F and 210F degrees.
This is simply the points the viscosity is checked. NOTHING MORE.
Now do you believe the oil does not get heavier above 210F or lighter below 0F? If you do you are wrong.
Every standard is a +/- 10% unless stated otherwise.
That is the STANDARD for rating.
The reason why a 20w-50 or heavier is not recommended is not flow but load on the engine systems and increased drag on the parts.
This drag equates into gas mileage.
Is 20w-50 required in an everyday street motor where Mileage is a concern?
No.
Is mileage a concern in a high performance engine?
No of course not.
Is protection a concern in the HP engine?
Damn right.
Trade off Protection for drag and mileage.
The decision is yours where those lines are drawn.
The only time the oil would be at the thinest viscosity would be when it is at it's coldest. That would ONLY be right at startup and not long after that.
Now the Heaviest viscosity would be at the hottest extreme and part in the motor.
Thats just the opposite of how oil performs in terms of temperature change. Oil, any oil, is more viscous cold and thinner (less viscous) as it heats up.
Thats just the opposite of how oil performs in terms of temperature change. Oil, any oil, is more viscous cold and thinner (less viscous) as it heats up.
You are correct. My choice in words was a bit confusing.
I should state that the Lowest Viscosity (Not really thinnest) and more viscous at higher temps.
The actual definition would be:
Viscosity is ordinarily expressed in terms of the time required for a standard quantity of the fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Since viscosity varies inversely with temperature, its value is meaningless unless accompanied by the temperature at which it is determined.
So in better terms it takes less time to flow (Thin) the when hot (Thick).
ford had trouble awhile back with their 4.6 motors. when they came from the factory they had 5-30 listed as the recommended oil. but they got thousands of cars they came in with junk motors that they had to switch to 5-20. i would run 5 20 and only 5 20.
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88 LX Hatch- Was fast...now parted out
06 Tungsten Grey GT- SOLD
07 Black GT- Custom Muffler Delete/BMR LCAs/Hurst Short throw/HID/Smoked Tails/Eibach Sportlines
synthetic 10w-30? 
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