It hasn't, at operating temperatures 5w20 has the same viscosity as 0w20.
Once the engine is warmed to normal operational temperatures, everything is fine.

For example, today I started my truck and ran it for 10 minutes before I went to work today (it was -34*C/-29*F). Since we get such cold winters, I have completely blocked my radiator off, with a large piece of cardboard in my grill.
Even with 10 minutes of warm up my truck is close to operating temperature after about 1 mile of driving I merge onto the highway, I am @ operating temperature. I merge onto the highway set my cruise control, and watch/feel MDS engage.

My gas mileage has increased for several reasons:
1. Its winter, colder air temperatures = denser air = run richer
2. Warming up my truck 5-10 minutes before I leave for work
3. Snow = Increased rolling resistance
4. 305/50/20 tires.

However after I made the switch, I noticed no difference in gas mileage, and I drove roughly 60 miles/100km to and from work each day. Same route. Week after week my gas mileage is +/- 0.5mpg. Depending on temperatures.

 

In the original testing of MDS operation the 0W20 oil was probably not widely available and for cost of testing reasons they prolly figured it's not worth the benefit of doing the test now since the 5W20 is satisfactory.

If I lived in a super cold climate I would try the 0W20 without hesitation.

 

Again... 0w20 and 5w20 have the very same viscosity at operating temperatures.

Therefore, it wont affect MDS.

The difference between 5w20 and 0w20, is the starting thickness.

Example.

Oil type...Thickness at 75 F... at 212 F...at 302 F

Straight 30...........100...................10...........3
10W-30.................75...................10........ ...3
0W-30...................40...................10...... .....3

 

I know on my previous car, 08 Mitsubishi Evolution X

There were 2 maintenance schedules, Normal and Severe.
Based solely on the fact that I lived in Canada, Mitsubishi insisted I and all Evolution X owners in Canada follow the Severe maintenance schedule, based on the fact that Canada has such a "harsh" environment.

Now if only Mitsubishi factored our cold climate into the equation when they designed the AYC pump. Once Temperatures his about -30*C the pumps fail, and they need to replaced at a tune of $2400. Thankfully its under warranty

 

Don't get me wrong, your theory has merit, but I still don't believe it's worth risking your warranty. If your engine should ever need warranty work, and you get a less than honourable and ethical dealership, you may be in for an uphill battle.
Guess it's up to the individual to make the decision.

 

Really? Because as long as you're operating the vehicle within the temp range that Chrysler says the Hemi can operate in then I'd say the factory-recommended 5W-20 is just fine. Why try to out-think the factory? Are you technically correct about the 0W-20 thing? Perhaps. But it doesn't matter because the factory already says the engine works correctly with 5W-20 in the same temps and doesn't need 'better' viscosity.

Now, if you plan to run the Hemi in a temp range BELOW what the factory says it can be run in with 5W-20 then by all means go ahead and find an alternate solution.

Rob

 

Its not a theory, its scientific fact.
Lab tested and proven.

Chrysler/Dodge Canada should recommend 0w20 as atleast a winter oil.

5w20 and 0w20 have different starting thicknesses and viscosities.

If you drive 10km and your oil is too thick, it wont properly coat your engine components. 0w20 will be thinner on initial start up, and give a better coating property then 5w20 on cold start.

Better engine coating = less friction = less wear

 

OMG, its like explaining to a brick wall.

at 212*F 0w20 and 5w20 will have the SAME Thickness/Viscosity as one another.

Where 0w20 is better is in COLD climates, where you have to start a cold motor. 0w20 will be thinner vs 5w20 at 75*F or 32*F or even -30*F

 

None of this above will be worth a hill of beans when your dealership tells you to go take a hike should you ever require warranty service on your engine once they realize you second-guessed them and used a different oil from what they clearly state.

I've owned many cars in my time, and have modified some of my sports cars. Some changes were clearly an improvement, but that argument fell on deaf ears once the Dealership Service Dept. realized you 'improved' their design and service recommendation. Been there, done it. Unfortunately it seems you'll have to go through it also before you learn your lesson.

 

I'm not saying your wrong on your tech specs. Just that it doesn't matter. Chrysler doesn't require thinner, 'better' oil just because it is cold out. Just use what the manual says and you won't have MDS worries or warranty issues. Or use whatever you want. I don't care. I'm just trying to say there's no value in your idea because the factory is OK with 5W-20.

Rob