Haddaddy

I’ve always put 0W40 in my 2020 c43 for the last 3 years living in the Boston area. Now my mechanic wants to put 5W40 instead, I understand the high temperature are the same and he was arguing even at cold temperatures are pretty much the same (clearly if it was the same it wouldn’t have two different makes for cold temps..) what do y’all usually run and do you see a big difference between the two?

I also can’t find a chart online that dictates what exact cold temps 0W & 5W run better at, anyone know these #?

Crito

SAE J300:
https://en.wikipedia.org/wiki/SAE_J300

jonathan358

Boston is not that cold, I would run 5W40 year-round without worry.

I live in the warm parts of Canada and have been thinking about using 5W40 for the summer months. Anybody try the new Castrol Euro Formula?

Crito

And just to rant a little, this is a perfect example of how idjuts with too much authority can really **** something simple up. Some people argue the first is a winter grade and the second is a weight. some argue both are weights. Some people argue they're both grades. And a surprising number of otherwise intelligent people honestly believe their oil turns thin as water in the winter (0 weight) and gets thick as molasses in the summer (40 weight). If the Three Stooges who came up with this convoluted system had just used the same scale for the first and second numbers, none of this confusion would exist. And the dash (0W-40) implies a range to most people BTW. So it should be 5W/40 at the very least. OK, I'm done...

AZC43

MB dealership here in Arizona, says 5w/40 for the '23 C43 as the "manufacturer spec." Who knows?

Crito

Manufacturer spec is the best oil to use. And usually your owner's manual knows but I own an electric MB.... My brand new Jaguar F-Pace SVR specifies STJLR.03.5006 in the book inside my glove box though, so I'm using this instead of the "special Castrol" (expensive but except for UV dye exactly the same as cheap Walmart Castrol) only the stealership can get:

MatthewJ

For anyone looking to read more into the weights, grades and viscosities : check this 7 chapter knowledge base :
https://bobistheoilguy.com/motor-oil-101/

My takeaway from it was no mater what ambient temp you live in, the oil will still be too viscus for what the motor is designed for (in our case 40wt). Startup and this thick oil condition is where wear occurs. So the closer you can get the oil to 40wt viscosity at startup temp the less issues you will have with wear and lack of lubrication of tight tolerance areas. A 0W/40 formula is thinner at startup than a 5W/40 while still maintaining the same 40 weight at operating temp, both are still too viscus for what the car wants to run at. So why choose the 5W? Unless you are a trying to compensate for out of tolerance gaps and need thicker oil to slow down leaks (think BMW guys running 10w50).

jonathan358

Cooling is a big factor for performance applications in which insufficient heat transfer at high temperatures may result in overheating. This can lead to problems such as breaking down of fluids and oils, thermal expansion causing over-pressurization and friction, warping of cylinder heads and rods, cracked engine blocks, and excessive exhaust valve wear. Of course most of these drastic events usually occur due to other factors like leakages or faulty components, but they do need to be considered when pushing the car to its limit.

Although 2 oils of different cold temperature performance, but same high temperature performance, may have the same lubricity when new, the viscosity index modifiers used to decrease viscosity at low temperatures tend to break down faster thus reducing performance at both ends.

Arguably, if you live in the desert with 30+*C ambient temps, having slightly less viscous oil during startups will have little to no difference in wear compared to the wear that occurs at 120*C. Modern engines usually have cylinder bore linings to help reduce friction/increase "lubrication" whereas nothing can be done to help at higher temps. Not to mention newer vehicles are built to higher tolerances and the lubrication matters even more at the upper range.

MatthewJ

I don't disagree, and I think your points are why I monitor oil temp real time and don't exceed 5k on change interval on a modified setup where heat input can be pushed.
FWIW I rarely exceed 200* engine oil temp. And never get on it before 160*.
5k changes are probably overkill as the modified have been shown to exceed even the 10k limit, but oil and filter is cheap insurance.

jonathan358

I guess you're right: if you keep the oil changes extremely frequent, then using new 0W-40 is probably best in the long run!

Still going to try 5W40 though for the summer because I am lazy and do 10-15k KM intervals