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Discussion Starter · #1 ·
Without getting into the whole, "The engineers know more than you do", or "Just use what the manual say's", arguments, has anyone gone to 0W-40 or 5W-40 in their WK 2, 5.7 HEMI's without having any issues? Everything I have read on this shows that both the 5.7 HEMI and the 6.4 HEMI have identical VVT and MDS Systems. That being the case, the 6.4 HEMI's are running 0W-40 per the manual.

It's a little hard to believe that an increase of just 40 cubic inches in the same type of engine would mandate a different oil. And if someone were to say it's because the 6.4 is a more powerful, high performance version of the 5.7, I would say that's pretty much a testimonial to the fact a heavier weight oil protects better. Why else would they recommend it in a larger, more powerful engine?

Anyway, I just wondered if some of you have made the change, what your results were after doing it?
 

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They are different engines, designed to use different oils. Why do you want to go thicker ? thicker oil is of no benefit, cold wear will increase, also MDS will not work right, rough running. My 5.7 has 170k, runs perfect on 5w20.
 
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Discussion Starter · #4 ·
SRT has MDS?
I'm not sure about the the SRT and the 391 Scat Pak HEMI's. But I'm pretty sure the standard 6.4 HEMI in the Ram pickups all do. Regardless, they all have the same VVT System, and all use 0W-40.
 

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I'm not sure about the the SRT and the 391 Scat Pak HEMI's. But I'm pretty sure the standard 6.4 HEMI in the Ram pickups all do. Regardless, they all have the same VVT System, and all use 0W-40.
My girlfriends 2015 Scat Pack Charger with the 6.4 Hemi had the MDS...
 

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I've asked the same question because I tow a 6500# trailer and regularly run 2500-3000 rpm for hours at a time. Tried 5W40 and the VVT hydraulics that control the cam phasing were all messed up. Wouldn't switch cam timing till past 5,000 rpm so lost pulling power up grades on the highway. Not sure the differences between the 5.7 and 6.4 in the bearing clearances, VVT hydraulics, cams and lifters but if the factory thought they could get away with 5W20 for the bigger engine they surely would even for a few tenths of mpg for fleet fuel economy numbers.
 
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Back in the day, for the most part, thicker oil ment better protection. Without getting into paragraphs of technobabble, if the engines VVT and MSD have identical and interchangeable parts, oil pumps, passages and filters, etc. then maybe...

Engine oil has multiple functions in the engine. Oil not only lubricates, it is a hydraulic fluid, cools, cleans, prevents oxidation, etc. Different weight oil is critical for the proper function of moving part with increasingly tight design tolerances. What was discovered, about 100 years ago, oil might be functioning fine in an isolated area such as a lifter, but if the oil is to thick to flow in or out of that component, it will likely be damaged for lack of fresh, clean, cool or warm oil.

Systems such as VVTs and MSDs are designed to preform very precisely at certain pressures and flow rates several thousand times a minute. Interrupting that timing with a different viscosity will cause issues with performance and wear.
 

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Discussion Starter · #8 ·
My girlfriends 2015 Scat Pack Charger with the 6.4 Hemi had the MDS...
If I'm not mistaken, all the 6.4 HEMI's with automatic transmissions have MDS. The manual transmission models with the 6.4 HEMI's do not have MDS.
 

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Discussion Starter · #9 ·
Back in the day, for the most part, thicker oil ment better protection.
It still does under high heat and RPM, along with heavy load conditions. No question about it. The problem today is with all of the techno crap designed into these engines, is if it's tolerable to use it. That and CAFE mileage demands.
 

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From: Jeep Grand Cherokee WK2 - Maintenance information and schedules

0W-40 (6.4 V8 Hemi)
MOPAR® API Certified SAE Full Synthetic engine oil

Pennzoil/Mopar p/n 68171066PA, MSRP $10.10/quart

For best performance and maximum protection under all types of operating conditions, the manufacturer only recommends full synthetic engine oils that meet the American Petroleum Institute (API) categories of SN. The manufacturer recommends the use of Pennzoil Ultra 0W-40 or equivalent MOPAR engine oil meeting the requirements of Material Standard MS-12633 for use in all operating temperatures.

NOTE: The fast-acting cam phaser system (Variable Valve Timing) on the 6.4L engine was designed to utilize synthetic 0W-40 viscosity oils.
 
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The O.M. says the MDS timing is calibrated to 5W-20.....
For another version of the engine the designers may calibrate the timing for another weight oil...
But I think only the 5.7L has MDS..... ....Don't know about the 6.4L in the Pick-Ups but all the other version of the HEMI in the WK2 and LX platforms I was pretty sure do not have MDS.... SCMIIW

Yes, the other versions do have VVT even if they don't have MDS, but again, the designers could have recalibrated the timing and activation for a different weight oil...

Considering what is going on with the MDS and the parts that are deactivating, I would not want to mess with it....

Yes, generally a thicker oil will protect better up to the point it doesn't flow fast enough through the engine, so it is possible too thick an oil could protect worse, but we're talking a big increase in viscosity, not going up 5 extra points on the viscosity....
Thicker oil does create more parasitic energy loses from the oil pump, so the manufacturers do have an interest in using a thinner oil that still protects adequately, for energy savings and various regulations and pressures that go with that...
Synthetic protects better than conventional or conventional/synthetic blends, seems to me that is the better way to go for the 5.7L if you want better protection....
Group IV Synthetics protect better than Group III Synthetics, for even more protection.... ....most of the big name brand synthetics on the store shelves are Group III, the boutique or exotic name brands that aren't on most store shelves and cost more are group IV oil, brands like AMSOIL, Redline, Royal Purple.... ....keep in mind some of those exotics have started offering Group III oil alternatives at lower prices, so just don't assume you're getting Group IV because of the name on the bottle.... ...also keep in mind Group III is still superior to conventional oil, you don't have to go to the lengths of getting Group IV for better protection....
 

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Found this on the Wiki for the Hemi engine....
"The production version of the 392 HEMI was launched in the 2011 Dodge Challenger SRT8 with variable camshaft timing as well as MDS in cars with automatic transmissions."
 

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It still does under high heat and RPM, along with heavy load conditions. No question about it. The problem today is with all of the techno crap designed into these engines, is if it's tolerable to use it. That and CAFE mileage demands.
Simply put, viscosity is the resistance of a fluid to flow and oil viscosity changes with temperature. The higher the temperature, the lower the viscosity.

In terms of just lubrication, a thicker oil will protect better under certain aspects of high heat conditions, under heavy loads and seal better. Thicker oil does not necessarily protect better with high RPMs or cold starts or tighter tolerances. In fact, heavier oils can oil starve bearings and other components when cold or high RPM causing damage. Thicker oils take longer to warm up and cool down in your engine.

Emissions requirements from well-intentioneded but vote seeking politicians can be a giant Pain. However, an efficient running engine usually means more power and better mileage. Higher viscosity oil takes more power to pump the oil and turn the engine.
 

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I've asked the same question because I tow a 6500# trailer and regularly run 2500-3000 rpm for hours at a time. Tried 5W40 and the VVT hydraulics that control the cam phasing were all messed up. Wouldn't switch cam timing till past 5,000 rpm so lost pulling power up grades on the highway. Not sure the differences between the 5.7 and 6.4 in the bearing clearances, VVT hydraulics, cams and lifters but if the factory thought they could get away with 5W20 for the bigger engine they surely would even for a few tenths of mpg for fleet fuel economy numbers.
In terms of hydraulics (and in a nutshell), going from 0W to 5W changes the cold viscosity rating from about -22°-ish to about 0°F. BTW, the "W" stands for "Winter". Even though 0W40 and 5W40 are a multi-rate viscosity, those viscosities have operating windows. The cold viscosity rating has an effect on the overall combined viscosity rating. While it may have little effect at high temperature, it can affect it's combined warm temperature viscosity window by several (8-10) degrees.

The VVT and MDS hydraulics are designed to operate at a certain oil viscosity and RPM. If normal engine oil operating temperatures are 212°-ish, the engine RPM and/or oil temperature may need to increase for the VVT to operate within it's designed hydraulic parameters when using a thicker oil. In your case it was nearly double the RPM.

Not all oil weights between manufacturers are exactly the same. Like most things, viscosity has a tolerance, plus or minus a certain amount. Some oils can meet standards, others exceed them. Mopar engineers design the 5.7 engine with VVT and MDS to perform with Pennzoil synthetic 5W20. While Valvoline is arguably a better oil than Pennzoil, and Valvoline synthetic 5w20 is approved for the 5.7, however, using the Valvoline my mileage dropping 3-6 MPG during cooler weather. Now that it has warmed up, 117° in Phoenix yesterday, my fuel mileage has improved over 15% and I have noticed an increase in power. Of course I am chalking this up to Valvoline exceeding viscosity standards.
 

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The "W" stands for Winter, already mentioned. It means the oil has passed a pour test. They chill the oil to like -40°F, pour it on a flate plate like 8" across and it has a minute to flow over plate and drip off the side. I may be wrong on some of that, but the basic idea is to test if the oil will actually flow at extreme cold, then it gets "W". If the oil can't pass the test, then it doesn't get the "W".

There are 10-30 oil that will turn solid in -40°F or less, that is why they have the "W" that usually has some additives to assure it doesn't solidify at extreme cold and that is what you'd want in extreme winters.
 

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All of which is why I just had my oil changed again this morning at my dealer using the 2015 5.7 hemi specified 5W20 factory synthetic oil. Warranty for another 35,000 miles, I'll stick with what the factory specifies.

Which is a shame, I have cases of Redline oil in my garage that I'd love to use but the lightest weight I have is 5W30
 

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Without getting into the whole, "The engineers know more than you do", or "Just use what the manual say's", arguments, has anyone gone to 0W-40 or 5W-40 in their WK 2, 5.7 HEMI's without having any issues? Everything I have read on this shows that both the 5.7 HEMI and the 6.4 HEMI have identical VVT and MDS Systems. That being the case, the 6.4 HEMI's are running 0W-40 per the manual.

It's a little hard to believe that an increase of just 40 cubic inches in the same type of engine would mandate a different oil. And if someone were to say it's because the 6.4 is a more powerful, high performance version of the 5.7, I would say that's pretty much a testimonial to the fact a heavier weight oil protects better. Why else would they recommend it in a larger, more powerful engine?

Anyway, I just wondered if some of you have made the change, what your results were after doing it?
My son had a 5.7 in his ram pickup. He switched to a heavier weight oil and the engine would shut down when i went to switch to 4 cylinder mode. Switched back to the standard oil required by the book and it gradually starting working right. No one seemed to know what the problem was. Those hemi engines will not function properly with the wrong oil in them.
 

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Huh? Do the RAM Trucks have the ability to manual activate the MDS?

The MDS when it goes to 4 cylinder mode, deactivates the valves to 4 cylinders so they remain closed. The air trapped inside the deactivated cylinder compresses as the piston goes up, and then assists the piston as it goes down. It acts likes spring to recover the energy lost from deactivating the cylinder. The valves have to close with precise timing to trap the proper amount of air.

The O.M. says the MDS is calibrated for 5W-20 and not to use another viscosity.

If you trap the wrong amount of air inside the cylinder, because the valves are slow in deactivating in the closed position at the exact moment, and the engine already is low on torque and power since its 4 cylinders, I can see that easily stalling the motor.

Valve trains can be destroyed from impacts created by lash, I don't know if valve deactivating slower than they should could cause that, but its possible. Personally I wouldn't experiment with my valvetrain, that is already torturous stresses from the geometry necessary for a HEMI, and O.M. says not to. I just wouldn't risk it.
 

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Rsched this when I bought my 2020 JGC Hemi. Specified oil required for cylinder deactivation. At that time, factory oil was mineral.
 
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