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Ford Recommends 5w50 Now?

muzzo

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Bearing clearances are what establish the viscosity required, primarily. Tight clearances = low viscosity oil, loose clearances = heavier oil. It's not a bean counter decision, it's a function of the design. And of course there's more to it.

Improved modern production tolerances have allowed OEMs to use tighter bearing clearances and lower viscosity oils which help in efficiency and hitting fuel consumption targets. Counter-intuitively, the tight clearances also increase the load capacity of the bearing for a given journal diameter, but the decreased oil film thickness leaves less room for error. Higher than normal cylinder pressures due to boost or nitrous demand an oil with higher film strength to maintain bearing capacity without collapsing the oil film thickness to zero. Very high cylinder pressures at relatively low RPM is the main reason diesel engines use 50 weight oils along with larger bearings and clearances. For a gas engine, basically don't spray on the hit unless your motor is built for it, or you'll quickly introduce your rod bearings to your crank.

This brief article explains this relationship well: https://blog.k1technologies.com/bearing-clearance-and-oil-viscosity-explained

Mechanical shear of the oil film and heat both play a role in diminishing the viscosity of your oil. This is where the quality of your oil may be more importance than the viscosity.

I've had a half dozen cars now with OE or aftermarket forced induction, so I've done a lot of reading on oil and here's my $.02

- For an OE F/I application I use Mobil 1 in the recommended weight. It's cheap and really good. If boost is increased from stock I'll go up a bit in viscosity. My Audi regularly sees 20-22+ psi so I use 5W40 Euro instead of 5W30. Engines built for boost will typically have larger bearing clearances and a higher flow oil pump to suit. The shear forces on the oil film are lower which reduces oil viscosity loss due to mechanical shear, so the need for an oil with exceptional "shear stability" is not as great. The trade off is needing a larger journal diameter to maintain the bearing load capacity and reduced efficiency.

- For an aftermarket F/I application I use Amsoil and go up a step in viscosity. A naturally aspirated engine will generally have tighter bearing clearances than one built for boost. Amsoil does have higher shear stability than Mobil 1 so you get better protection without having to go full race weight on your oil. 5W30 Amsoil Signature is a great all-around option for a boosted Coyote street car even if it sees occasional hard use.

- The biggest reason to go up to a 50 weight for a healthy gas engine is extreme heat. If it's truly a track slut, then go for the 5W50. There's a reason the GT350 has an oil temp gauge in the dash (although I think it's a derived value, not actual). I've got a lot of experience with air/oil cooled bikes and they all require heavy 50 or 60 weight oils because of the heat. If you've ever cooked a big twin in parade traffic then checked your oil you'll know it's as thin as water, maybe less.

So will it hurt to put 5W50 in YOUR car? Probably not, but bear in mind that all else being equal, heavier weight oil will yield higher oil pressure, but lower overall flow. Oil has 3 jobs - to act as an oil film bearing surface, to provide cooling, and to provide lubrication - in that order of importance. Your 50 weight might improve oil film strength, but at the detriment of cooling and lubrication which depend on flow. Unless your operating temps are up high enough to warrant it, skip the race weight oil and stay closer to what the manufacturer recommends.

/nerdfest
In South Texas summer heat is 100+, with heat index’s of 115 to 120. 5w 30 still works fine.
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BmacIL

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You won't lose any oil flow volume to parts that are force fed by the positive displacement oil pump.
That's not how that works. Just because there's positive pressure doesn't mean you won't decrease flow with a higher viscosity.
 

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It's all about the additives, not the viscosity for today's oil IMO. Personally I use 5w20 Pennzoil Ultra Platinum. It's a TRUE synthetic oil, made one carbon molecule at a time from natural gas. Almost all other synthetics are actually blends of crude.
 
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That's not how that works. Just because there's positive pressure doesn't mean you won't decrease flow with a higher viscosity.
Go study up on how a positive displacement oil pump works. As long as the pump isn't in pressure relief, then the volumetric output of the pump will be the same. So like I said, areas in the engine that are force fed by the oil pump will still get the same oil volume. The oil pressure will be higher with thicker oil in order to supply the same oil volume, that's how it works.
 

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Go study up on how a positive displacement oil pump works. As long as the pump isn't in pressure relief, then the volumetric output of the pump will be the same. So like I said, areas in the engine that are force fed by the oil pump will still get the same oil volume. The oil pressure will be higher with thicker oil in order to supply the same oil volume, that's how it works.
No. Pressure when talking about flowing fluids is resistance to flow. Study some fluid mechanics (I have). Just because the volume immediately exiting the pump is fixed does not mean that the flow at the bearings and up to the head is the same. Higher viscosity oils flow worse (and because of that, cool worse), but have thicker films and resistance to shearing.
 

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. So like I said, areas in the engine that are force fed by the oil pump will still get the same oil volume. The oil pressure will be higher with thicker oil in order to supply the same oil volume, that's how it works.
That is NOT how it works. Smaller diameter passages will keep the same pressure, at LESS volume, just like larger diameter passages will have less pressure with more volume. Hence the need for proper viscosity oils, they're able to maintain volume & pressure. SO Fords 5w20 was deemed the best solution for what the engine was designed to do. Just my humble opinion of course.
 

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No. Pressure when talking about flowing fluids is resistance to flow. Study some fluid mechanics (I have). Just because the volume immediately exiting the pump is fixed does not mean that the flow at the bearings and up to the head is the same. Higher viscosity oils flow worse (and because of that, cool worse), but have thicker films and resistance to shearing.
Yes, pressure is resistance to flow, and that's why the pressure goes up when the same volume of thicker oil is leaving the PD oil pump. If the volume leaving the pump is the same, then how can the flow to pressurized parts be less? It's not, unless the pump is in pressure relief. It's a good practice to not do high revs with any viscosity of oil until the oil heats up and thins down so the oil pump doesn't hit pressure relief.

So you think Ford and others say to run thicker oil for track use because parts are getting less oil flow from the PD oil pump?
 

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That is NOT how it works. Smaller diameter passages will keep the same pressure, at LESS volume, just like larger diameter passages will have less pressure with more volume. Hence the need for proper viscosity oils, they're able to maintain volume & pressure. SO Fords 5w20 was deemed the best solution for what the engine was designed to do. Just my humble opinion of course.
You're missing the whole point of a positive displacement oil pump. The oiling system in an engine is not a pressure sourced oil supply like the water system in your house.

A PD oil pump will force the same volume through the system if it's not in pressure relief. When there's more resistance (ie, thicker oil) to force the same volume through the system, then the pressure goes up.
 

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No. Pressure when talking about flowing fluids is resistance to flow. Study some fluid mechanics (I have). Just because the volume immediately exiting the pump is fixed does not mean that the flow at the bearings and up to the head is the same.
I'm not understanding this. How can the rate change unless the passages balloon or the oil gets compressed?
 

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I have a 16gtpp and a 97 f150 4.6 first year of the modular engine. The manual on the truck said 5w30 but ford sent an official bulletin changing it to 5w20. It is due to the engine clearance and tight tolerances and the chain guides. My mustang I've changed the oil myself since new with motorcraft 5w20 syn blend and I've never heard anything from the engine its quiet from start up to shut down. I also use motorcraft filters. 22k miles no problems at all. But mine is a garage queen and not driven hard except spirited driving on weekends of course. As for the truck it's at 140k miles and using 5w20 it has never had any noise either.
 

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I have a 16gtpp and a 97 f150 4.6 first year of the modular engine. The manual on the truck said 5w30 but ford sent an official bulletin changing it to 5w20. It is due to the engine clearance and tight tolerances and the chain guides.
More like due to Ford's commitment to CAFE. Ford back specified to 5W-20 to appease CAFE and get credits.
 

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Man if some of you guys seen how F1 manages the oil / viscosity / etc., you'd change your tune on what you think you know vs why the manufacturer's do it their way. F1 is an extreme example, but relevant.
 

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Man if some of you guys seen how F1 manages the oil / viscosity / etc., you'd change your tune on what you think you know vs why the manufacturer's do it their way. F1 is an extreme example, but relevant.
It's all about maintaining an adequate MOFT (minimum oil film thickness). You can run lower viscosity oil as long as the temperature is kept low enough to maintain enough MOFT to prevent metal-to-metal contact under severe conditions. Any race car like NASCAR or Indy is going to employ some pretty large and effective oil coolers to keep the oil from becoming too thin from heat, which makes MOFT thinner.

Race car engines are meant to last the race, not 250,000 miles, so that's another factor when they consider what oil to use. Race teams don't care if there's some wear, as long as the engine makes peak HP for the whole race and it doesn't blow-up.
 

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Man if some of you guys seen how F1 manages the oil / viscosity / etc., you'd change your tune on what you think you know vs why the manufacturer's do it their way. F1 is an extreme example, but relevant.
Are you really comparing an exotic F1 engine that runs for hours and hours at WOT at 16,000rpm to a run of the mill mass produced car/truck engine?

Just because they both have pistons that go up and down in a cylindrical piece of metal doesn't mean the same principles apply.
 

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Are you really comparing an exotic F1 engine that runs for hours and hours at WOT at 16,000rpm to a run of the mill mass produced car/truck engine?

Just because they both have pistons that go up and down in a cylindrical piece of metal doesn't mean the same principles apply.
Yep. I am comparing the too. Same Principle most definitely apply. Intake / compression / power /exhaust strokes, oiling, fuel delivery, all the same. POint being is that the more precision in tolerances your engine has, the lower viscosity engine oil you can use. Hence the 0w5 weight oil they use. Fuel diluted as well. 40/50 viscosity oils are for like .030+ bearing clearances, supercharger application where extreme pressure in put on the first 2 main bearings, pressure put on the compression and oil rings, yada yada. 5 weight isn't the cause of wear in f1 engines, extremely tight, accurate clearances are. So I wouldn't worry about the 5w20 in our engines where tolerances replaces precision.
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