Originally posted by 02f1504x4
I have a 2002 f150 and a mechanic friend of mine said that he runs 10w-30 in his 5.4 for better protection. I was thinking of doing the same but figured I would ask a few more people, with more knowledge in this subject than me. Will this hurt the truck in any way or does it really even matter? Any information would be appreciated.

... let me explain the basics of viscosity and oil nomenclature: For example a 10W-30, 5W-30 and 0W-30 oil are all 30 weight oils. The differences occur in that the 10W, 5W and 0W each is a little bit different in cold weather (W stands for weight in winter weather). The 10W-30 acts like a 10 weight oil in winter weather until it warms up and then it is a 30 weight oil. The 5W-30 oil acts like a 5 weight oil in winter weather and when it warms up is a 30 weight oil. Same theory holds true for the 0W-30 oil. The differences are ever so slight that you would not be able to differentiate which one was in your engine without the use of specialized engine testing equipment. In fact 5W, 10W and 0W are strictly empirical numbers. In order to discern the differences one needs to review the kinematic viscosity of each lubricant. Kinematic viscosity is measured in Centistokes and is essentially the amount of time, in Centistokes; it takes a lubricant to flow through a fixed orifice at both 100 deg. Celsius and 40 deg. Celsius. For example, the kinematic viscosity, at 40 deg. C or AMSOIL 5W-30 is 59.5, AMSOIL 10W-30 is 66.1 and AMSOIL 0W-30 is 57.3. So as you can see the values are extremely close to each other.

In respect to the 5W-30 vs. the 10W-30 there are virtually no major differences other than the 10W-30 is formulated for turbocharged engines. Therefore when you use it in a non-turbocharged engine you get that extra measure of protection. The 5W-30 is often used by those customers that go exactly by the book and will only use what their owner’s manual says.

In my business I recommend the 10W-30 or 0W-30 even when the manufacturer’s recommendations call for a 5W-30 or a 5W-20. You see, I am an engineer at one of these automotive manufacturers here in Detroit, MI and I will let you in on a little secret: the auto manufacturers like to use lighter viscosity petroleum oils so that the vehicles get better CAFE (Corporate Average Fuel Economy). Vehicles and components are also engineered to have a finite life within certain durability mileage ranges and test cycles and are tested using the petroleum oil that is specified by the manufacturer.

CAFE is mandated by the Federal Government and it is the average fuel economy of the entire vehicle line a manufacturer produces. Big trucks and SUV's are highly profitable where small cars are not, so in order to get the CAFE #'s reported to the Federal Government higher and be able to sell more SUV's and trucks they use lighter viscosity oils to compensate like a 5W-30 or 5W-20 so fuel economy increases (only in controlled tests which is why you'll never notice any difference in your vehicle). These 5W-20 oils, in my opinion, are that these oils do not provide an adequate level of protection under extreme conditions and severe duty. This is why I will not recommend a 5W-20 lubricant for my customers.

In addition, when these CAFE tests are run they are run under strictly controlled conditions on a closed course test track and with specially tested lubricants and fuels which are all within specifications. In fact, they don't even use standard pump grade fuel like is sold at retail gas stations. They use Indoline. That is one reason why your vehicle may not achieve the fuel economy numbers stated on the window sticker.

It is my opinion that the auto manufacturers are looking out for their best interests, profits and repeat business when vehicles need to be replaced. They figure if you get a decent average service life out of your engine without any major problems then you will be satisfied & will trade it in or sell it and buy another one soon. If they manufactured a vehicle that was so durable that you didn't need to buy a new one very often new vehicle sales would decrease significantly.