Api oil app for 300 6 cylinder
will this help?
10W30 or 10W35 for the first 100,000 miles then 10W40 after that. 20W40 all the time in the south. Or single weight SAE 40 in a warm climate. The more multiweight it is the more the viscosity modifiers can break down and produce sludge, and there is less forgiveness for overheating.
A poster on another forum said he used 20W50 year round where the temperature goes down to -30F in some extreme cases and had no issue. He said he used thinner oil in another ford engine, not necessarily an inline 6, and it caused a lot of problems that weren’t present on the other engine that ran 20W50 when they were overhauled. This particular engine is known for being damaged by using too thin of an oil, but not too thick.
Where do you come up with this NONSENSE?? A 1960 opinion piece on “them new fangled oils”?
OP, use the oil specified for your truck. Period.
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Hi Lew43:
The Ford Owner’s Manual for your vehicle is at:
https://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/96f12og1e.pdf
On page 320 and 321, it says SAE 10W-30 is the preferred viscosity for temps down to -5F. And that in temps below -5F, 5W-30 may be used.
Were you looking for something more?
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I’d never looked it up, but I was going to say that engine would be fine with 10w30 or 5w30.
Only difference really is the cold viscosity. Considering the availability, I’d go 5w30.
Unless you’re towing a log truck in the desert. 
Are you disagreeing about single weight oils, such as SAE 30, having better high temperature performance, such as in an overheating situation, racing, or in air cooled engine compared to 10W30?
The manual says that synthetics are acceptable too.
You beat me to it. While I looked on line for the manual, you posted the answer.
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What if it was a 1960 inline 6 and the manual didn’t say synthetics were acceptable? That engine was produced by Ford for over 3 decades I believe.
Your post was full of useless advice. All modern engines are designed to use multi weight oils, which do NOT degrade in any normal use, like the OP’s F150. Referring to airplanes and race cars is not helpful.
The 10W30 viscosity becomes the SAE 30 viscosity once the engine warms up.
Tester
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Why would you use 10W30 or 10W40 in south Florida when you could use SAE 30 or 40? If it overheats there will be more damage done with the 10W and if an oil change is forgotten it will be mare damaging with 10W. It’s completely pointless to run multiweight in a hot climate. So you might have to travel north on short notice. If it doesn’t get below 10F just warm it up for a couple minutes and it’ll be fine.
I guess it’s the same reason why the oil pressure light is no hard to see, or in this case there isn’t a light at all, and there is no light or alarm for overheating. Ford wants to sell you a new vehicle, and if they can make it seem like it’s your fault for not maintaining the engine then all the better for them.
You do not understand how multi grade oil work.
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So how do they work then?
Google it…
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because when the engine is cold and you first start it up you want the 10w
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I did search it and often the first several search results are total bull crap. You can even see where they’ve copied and pasted the portions from other resources. It’s usually some crap that a non engineer person would believe as a justification followed by something to the effect of “Use what your manufacturer recommends”.
A cold start on an engine is when the engine isn’t at operating temperature.
It’s not where you live.
Tester
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I’m pretty sure 10W at 0 degrees Fahrenheit is thicker than SAE 40 is at 50 degrees Fahrenheit
Lots to read here for you: