[quote]The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold ambient temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a low viscosity at the engines operating temperature. The difference in viscosities for any single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers are added to the oil. These additives make the oil a multi-grade motor oil. The idea is to cause the multi-grade oil to have the viscosity of the base number when cold and the viscosity of second number when hot. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the base oil.
The API/SAE designation for multi-grade oils includes two grade numbers; for example, 10W-30 designates a common multi-grade oil. The first number associated with the W (again 'W' is for Winter, not Weight) is not rated at any single temperature. The "10W" means that this oil can be pumped by your engine as well as a single-grade SAE 10 oil can be pumped. "5W" can be pumped at a lower temperature than "10W". "0W" can be pumped at a lower temperature than "5W", and thins less at temperatures above 99°C (210°F). The second number, 30, means that the viscosity of this multi-grade oil at 100°C (212°F) operating temperature corresponds to the viscosity of a single-grade 30 oil at same temperature. The governing SAE standard is called SAE J300. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle.
Many new vehicles are marked to use 5W-20 oil (Honda, Ford, and more recently Toyota). Some ultra fuel efficient and hybrid vehicles are marked to use 0W-20 oil. For some selective mechanical problems with engines, using a more viscous oil can ameliorate the symptoms, i.e. changing from 5W-20 to 20W-50 may eliminate a knocking noise from the engine but doesn't solve the problem.[quote/]

from wikipedia, this section seems accurate to what I learned in school

 

I hate oil threads.

 

Motorcraft 5-50 is definately thicker than 5-30. I ran the 5-50 in my new motor and I have the GT500 oil pump in it. I switched to 5-30 and the motor quieted down significantly.

 

The heavier oils affect the VCT I think Ford has done enough research on what is good for the engine.

 

travelers and Bullitt995 know how to read! Check out my post about the VCT. That is the #1 reason why you shouldn't run anything thicker than 5W-30 in the 4.6/5.4 3V V8.

For those with 4.6/5.4 2V and 4V engines, run whatever you want to your heart's content. I haven't heard of any of these engines failing due to the use of a thicker oil, just make sure it is a fully synthetic 5W-xx. A 15W-40 or 15W-50 will cause wear during cold starts!

I asked Ford Australia about the recommended viscosity for their Falcon's (5.4L 3V and 4V engines) and they said 5W-30. I do enjoy the slightly higher gas mileage from running 5W-20. I figure by the time my engine wears out from using 5W-20, I could just swap in a more powerful motor or switch to a hydrogen fuel cell diesel electric hybrid that does 0-60 in 3 seconds.

 

I run 20W-50 in my motor... and I have lots of videos, too.

BTW, there has been absolutely zero negative affects with the VCT using the heavier oil.

 

Interesting

 

Running 20W-50 in SoCal may not show many problems especially in the summer, but I bet a UOA will show extra metal wear due to the cold starts.

How are you determining that the VCT is fully operational?

 

You don't have stock heads/cams do you? VCT is turned off on most high horsepower tunes.

 

Stock cams in P&P heads, with VCT still operational. Adam did not disable the VCT on my car.

 

Odd, you sure it's working? I don't even know what a VCT malfuction would cause.

 

A lot of you guys are still missing the technical issue here regarding casual use of heavier wt oil.

Heavier wt oil requires more horsepower to pump (less horsepower to the rear wheels), more of the heavier wt oil goes across the pump relief valve which results in less oil to the bearings(!) and valve train and makes for hotter oil. The more oil going over the relief valve shears those polymers that give the oil its higher viscosity characteristics at operating temperature there by shortening the useful life of the oil.

 

It probably won't cause problems with the VCT, since the viscosity of the 5-50 at full operating temp. is similar to 5-20 at a lower temp....maybe 140F. The VCT still works with oil at 140...heck it works at 100F, and the 5-20 is thicker at 100F than 5-50 at 212, I guarantee it.