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Discussion Starter #1
I tried searching this on the forum and online but I cannot find an answer for it.

People always say that when the External Ambient temperature is high then a higher oil viscosity is recommended. For example, 5w-30 or 5w-40. Their reasoning is because oil gets "thinner". But our vehicles recommend 5w-20 at all ambient temperatures.

:thk:
It is my understanding that the latter part of the rating, viscosity of "20" or "30" is the thickness rated at a temperature of 100 Degrees Celsius (212 Fahrenheit). I also know that if the oil runs excessively hot then it will oxidize and breakdown the chemical bonds, 250+ Fahrenheit for conventional and 300+ Fahrenheit for Synthetic.

:thk:
Here is my question, if the temperature outside is 32 degrees or 110 degrees the internal oil temperature will be maintained around 212 degrees mostly consistently. So then why would I put 5w-30 or 5w-40 in a motor that recommends 5w-20 if they will all be operating at 212 degrees (when warmed up) regardless of external ambient temperature?

If a vehicle recommends a thin oil I assume there is a mechanical part within the motor that has such a tight tolerance that thick oil would not be able to lubricate properly. Even at 212 degrees. I am also pretty confident that these oils have been designed, engineered, and tested to be able to properly lubricate the internal and prevent metal to metal contact. Even if the oil looks like "water".
 

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Keep in mind, there is a range of actual viscosity values for the rated oil. i.e. a 20 weight can have a 100 degree viscosity of 6.9 to <9.3. So, you could get a "heavy" 20 weight or a "light" 20 weight.

Also, as oil gets hotter, used longer, etc it will start to shear down to a lower viscosity. So if you started with a light 20 weight and it sheared...what do you have now? Some say that 20 weight itself is harder to shear simply because of its beginning viscosity already being low...but I dont pretend to know for sure (not a chemist, engineer, etc)

Likewise...you can get a light 30 weight that is barely above the range of 20 weight viscosity...and probably WOULD shear down to a heavy 20 weight after some use. The difference being that as the 30 weight aged, it would still be a heavy 20 weight, potentially protecting as well or better than fresh 20 weight.

Ill get my popcorn out, though, because threads like this always turn into some people saying 30 is better and some people saying the engine is fine on 20. Personally, I fall somewhere in between...my gut tells me some of the cam/lifter issues could be prevented (or at least prolonged) with oil that keeps a higher oil pressure throughout the RPM range (especially at idle). Ive watched the oil pressure at idle on my '17 drop to 34-35 psi with only 600 mile old conventional 5W-20. Where as with 2000 mile old factory fill, it was 38-39 psi. Is only 3 or 4 psi, but my gut also tells me that the higher pressure is getting oil to the lifters better than lower pressure.
 

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I agree - I have wondered why we can’t run 5W30 or 5W40 full syn in these engines. After all, they are a 5W when cold, a 40W on the hot side.

EPA fuel regs maybe?
 

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Discussion Starter #4
Thanks for the response. How do you know if you have a light or heavy 20 or 30 weight? Seems like I would want to run a light 5w-30 that shears down to a heavy 5w-20.

Also, I am wondering if running 5w-30 would damage the 5.7 HEMI because of the MDS since the 5.7 in the 2500 recommends 5w-30 without MDS. I always ran 5w-30 on everything so the idea of 5w-20 is hard to accept and why I am trying to do so much research on the topic. My wifes mini cooper also recommends 5w-20 and that thing has a turbo. :SHOCKED:
 

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Look on the internet for Used Oil Analysis (UOA) or Virgin Oil Analysis (VOA) for whatever oil you are thinking about using. The 100 degree viscosity results will be in those.

Lots of other good resources on the net (BITOG forum, PQIA.com, etc)

As far as MDS and heavier than 20 weight - thats another "break out the popcorn" issue. Some people said they had issues running 30 weight, some people said they've had no issues. But again, that could also come down to how "heavy" the oil is in its viscosity range.

Keep in mind, if you use anything other than 5W-20, you are technically at risk of engine warranty coverage being denied.
 

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Discussion Starter #6 (Edited)
I got a Blackstone Oil Analysis kit the other week. I still haven't done my first oil change so when I do I will put 5W-20. Then I will do my second oil change after 8,000 miles and see what the analysis results say.

*Edit*
For anyone curious about 5w-20 vs 5w-30 oil on HEMI with MDS, I found this post where a guy claims 5W-20 is recommended for the special valve lifters used on the cylinders that shut off.

dodgeforum /forum/dodge-magnum/17035-5w-30-ok-for-5-7l-hemi.html

Post scrambles my link for some reason...
 

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I agree - I have wondered why we can’t run 5W30 or 5W40 full syn in these engines. After all, they are a 5W when cold, a 40W on the hot side.

EPA fuel regs maybe?


The speculation is that 5W20 is for CAFE government regulations.


I will say that you can run 5W30 in your 5.7 Hemi because I am running 5W30 Pennzoil Ultra Platinum in mine right now and before that I was mixing 5W20 and 0W40 for roughly a 3W28 in the Ultra Platinum. My engine is smooth and quiet. As for the MDS lifters in the 5.7 I have read that they are the exact same part number as the lifters in the 6.4. The 6.4 is rated for 0W40. IMO 40 weight oil is unnecessary in the 5.7 but some guys have run it with no reported issues.
 

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The engine was designed for 5w20, you're not going to outsmart the engineers who spec'd the oil for the engine and using too heavy a viscosity can cause starvation issues
 

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In my truck, I have run 5-30. MDS was fine, however I got a backfire like bump on every cold start after the truck sat a while. I can only assume it had to do with the VVT operation as it does a full sweep on startup.
Next oil change went to 5-20 and it never happened again.
 

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The Pentastar 3.6L was "designed" to use 5W30 when it came out then all of a sudden we were told 5W20 was what you should use. The Ford 5.4's were "designed" to use 5W30 and a few years later Ford changed to 5W20. Engineers don't have your best interests at heart. They work for a company that has to follow strict government regulations for fuel consumption. 5W30 does not effect the MDS in any way, if it did the 6.4 could not run 0W40 since it uses the same MDS lifters in it.
 

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If 5W-30 is what you are after, look for a heavier 5W-20.

Just checking PQIA quickly, viscosity-wise, Castrol GTX 5W-20 is on the "heavy" end of 5W-20. This is assuming that the heavier weight will help protect better.

On the other hand, Im not quite sure what a dealer would do if you came in with a blown engine....do they really send the oil out and try to determine the exact weight thats in the engine at that time? And even if they did, is it possible to determine 100% it was a 30 and not a 20?

Also, if you check a VOA for Pennzoil Ultra Platinum 5W-30, the 100 degree viscosity is BARELY in the range of 5W-30. If it shears down even a little bit, it would "become" a 5W-20.
 

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The Pentastar 3.6L was "designed" to use 5W30 when it came out then all of a sudden we were told 5W20 was what you should use. The Ford 5.4's were "designed" to use 5W30 and a few years later Ford changed to 5W20. Engineers don't have your best interests at heart. They work for a company that has to follow strict government regulations for fuel consumption. 5W30 does not effect the MDS in any way, if it did the 6.4 could not run 0W40 since it uses the same MDS lifters in it.
They aren't the same engine so the idea that the same viscosity will work equally well in a 5.7 and 6.4 is flawed. The blocks are different, so are the heads. Are the oil passages the same? What about bearing clearances and solenoids.

Use whatever oil you like, by all means, but the idea that using other than recommended viscosities is better for your engine is wishful thinking at best. May as well use 15W-40 in all your engines

If 5W-30 is what you are after, look for a heavier 5W-20.

Just checking PQIA quickly, viscosity-wise, Castrol GTX 5W-20 is on the "heavy" end of 5W-20. This is assuming that the heavier weight will help protect better.

On the other hand, Im not quite sure what a dealer would do if you came in with a blown engine....do they really send the oil out and try to determine the exact weight thats in the engine at that time? And even if they did, is it possible to determine 100% it was a 30 and not a 20?

A UOA would determine that quickly, but I doubt they'd do a test like that unless there were signs of starvation without a clogged oil pump pickup.

I know some guys worry that if they use X brand oil and have a failure their warranty will be denied, but I think any dealer that is looking for an excuse like that to deny your warranty is probably going to cut corners and do a shoddy repair anyway.
 

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A UOA would determine what the viscosity is at the point the dealer sends the sample off.

By then, unless it was brand new oil, I would think the viscosity would be at least slightly different than when it came out of the bottle.

But I agree with your other sentiment....if they're going to deny deny deny, they would use any excuse possible and probably wouldn't need to get as far as viscosity testing. And yeah I wouldnt want them touching my truck at that point anyway.
 

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A UOA would determine what the viscosity is at the point the dealer sends the sample off.

By then, unless it was brand new oil, I would think the viscosity would be at least slightly different than when it came out of the bottle.

But I agree with your other sentiment....if they're going to deny deny deny, they would use any excuse possible and probably wouldn't need to get as far as viscosity testing. And yeah I wouldnt want them touching my truck at that point anyway.
It should still be close enough for the to tell if it was a 30 weight vs a 20 or 40 weight though. I do around 6000 mile intervals and the viscosity is always well within the range for a 5W20 on my UOAs
 

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Multi-Grade oil 5W - 40 can be broken down like this

5 degrees ( Winter ) the oil will flow through the smallest ports in the engine

40 = SAE 40 weight

You could just as easily use 0w - 40 for even colder weather

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0W or 5W - SAE 20 works great with the 5.7L w/ MDS
SAE 30 may cause the 5.7L w/ MDS engine light to come on

SAE 30 works great in the 5.7L without MDS

5W - 40 Light Duty is used in the Eco-diesel engines

15W - 40 Heavy Duty should be used in the Cummins engines
( 0W - 40 Heavy Duty oil could be in the Cummins engines too )
 

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Multi-Grade oil 5W - 40 can be broken down like this

5 degrees ( Winter ) the oil will flow through the smallest ports in the engine

40 = SAE 40 weight

You could just as easily use 0w - 40 for even colder weather

==================================

0W or 5W - SAE 20 works great with the 5.7L w/ MDS
SAE 30 may cause the 5.7L w/ MDS engine light to come on

SAE 30 works great in the 5.7L without MDS

5W - 40 Light Duty is used in the Eco-diesel engines

15W - 40 Heavy Duty should be used in the Cummins engines
( 0W - 40 Heavy Duty oil could be in the Cummins engines too )
Again, you need to take into account the allowable range of viscosity for a given grade.

5W-20 can be anywhere from 5.6 to <9.3 mm^2/s.
5W-30 can be anywhere from 9.3 to <12.5 mm^2/s

What this means is that I can have a 5W-20 that is almost a 5W-30, and I can have a 5W-20 that is barely a 5W-20. Its a pretty wide range, as you can see.

Applying it to MDS and 5W-30....I bet if you tried a 5W-30 on the higher end of the viscosity range, it might actually cause an issue (too thick). But if you tried something like Pennzoil Ultra Platinum (whcih even has the correct Chrysler cert), with a viscosity of 9.82, there shouldn't be much surprise if (when) it works JUST FINE, even with MDS.
 

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They aren't the same engine so the idea that the same viscosity will work equally well in a 5.7 and 6.4 is flawed. The blocks are different, so are the heads. Are the oil passages the same? What about bearing clearances and solenoids.

Use whatever oil you like, by all means, but the idea that using other than recommended viscosities is better for your engine is wishful thinking at best. May as well use 15W-40 in all your engine.


I never said they were the same engine I said the 6.4 uses the exact same MDS lifters. You worry about the heads, lifters and oil passages being different then tell me why you can use 5W30 in the 5.7's that came in the 3/4 ton trucks? In fact the owners manual recommends it if you are towing heavy. The only difference between those 5.7's is the 3/4 ton truck does not have the MDS lifters. What you call wishful thinking I will call research. I choose not to accept that everything the government and the vehicle manufactures say is fact. They look after their own interests and not mine.
 

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Plenty of guys on the other Ram forum running 5W30 and a mix of 5W30 and 5W20 in their 5.7 Hemi's with no problems. Some think that too thin of an oil (5W20 is like water)is behind the cam and lifter problems.
 
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