5W-20 or 10W30?

[greencrew]

Well done gopher, I would be proud to have typed it in that clearly. All I have to add is that the 5w20 spec is for a group III hydrocracked oil. It's more durable than either the 5w-30 or the 10w-20 oil. The trend has been that the oil mfgrs are getting better at designing additives and as a result the 5w oils are more durable at operating temp and provide better startup protection. Oil analysis of 5w-20 shows the oil does very well, just as it was desinged to do. That's good news for trucks that see a lot of cold starts, but not all that exciting for those in the hot hot southern country.

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[DrDevon]

...these engines operate well above 90F or any other ambient (air) temperature we see in the USA, so any time we start them here on Earth it is a cold start.

I would like to see the detailed mechanistic analysis fo why anyone would seriously recommend a 10w-xx oil when a 5w-xx oil is specified by the manufacturer. The film strength (protection) is a function of the viscosity, which is a function of temperature as mandated by the API/SAE spec. Doesn't matter how many times the oil has been cracked (whether type II, or VI or whatever); the viscosity specs are clear, and fluids meeting those specs will provide the tensile film required to protect against breakdown in the cylinder, whil eflowing through all the aperatures at the pressures submitted by the pumping system throughout the temperature curve.

Ford indicates (and has never wavered from) the 5w-xx oils. Works great.

[DOHC]

[quote]Originally posted by DrDevon
[b]

(I would like to see the detailed mechanistic analysis fo why anyone would seriously recommend a 10w-xx oil when a 5w-xx oil is specified by the manufacturer."

Thats an easy one. Some 10/30's will out perform 5/30's in both cold cranking and cold pumping.

" The film strength (protection) is a function of the viscosity, which is a function of temperature as mandated by the API/SAE spec. Doesn't matter how many times the oil has been cracked (whether type II, or VI or whatever); the viscosity specs are clear, and fluids meeting those specs will provide the tensile film required to protect against breakdown in the cylinder, whil eflowing through all the aperatures at the pressures submitted by the pumping system throughout the temperature curve."

Please explain temperature curve ? Thats a new one on me.

That is called HTHS " High Temp/High Shear not tensile strenght and that does not come from the base oil alone. This is measured with the additive pack in formulation. Thats why you will see a very few 10/30's with the ACEA A3 rating vs the most common and lower A1

Hope this helps

[greencrew]

Good points DOHC.


Also, keep in mind that both a 10w-xx oil and a 5w-xx oil need to be pumped up to the system before it can start to lubricate. That's not the issue, the issue is how well it flows after 30 seconds.

To really understand the issue you need to turn an oil container upside down at -30F and realize that nothing is comming out.

Now you know you have a real oil flow isssue is when you start the engine.

[webmack]

I know this is an old thread but its related to my issue here: 1997 Expedition EB on Castrol 10W-40

Could one you guys offer some advice?

[glc]

It's been offered in that thread.

[jethat]

Trust Fords recommendations. 5-30 for your truck. I dont think 5-20 would hurt it but Ford recommended 5-30 for that year.