How many times have you switched sides on the thick vs. thin debate?

My 2014 Pathfinder specifies 0w20 or 5w30, I've used 0w20, 5w20, 5w30, 10w30 and 10w40 in it with no issues.

Looking at the service history, it only had 5w30 with the previous owner, and the first time it had 0w20 was the first free courtesy oil change it got from the dealership I bought it at.

I haven't seen any significant difference in fuel mileage with all the different grades of oil I've used but the engine sounds smoothest when it has 10w30 so I usually run that or 5w30 plus a bottle of STP.
 
For the M375 at left, 20W-50 is OEM for mild climates, as per FSM. Carb builder and ex-Dodge factory mechanic also recommended it.
I might try 10W-40 HPL as per previous thread, a "modern" oil. Temps here are 25F to 100F.

I get the part where cold oil has to flow through the (flat) tappet orifices etc, but starter/cranking has never been an issue: the B3500 and M375 both fire on the first cylinder. It almost seems better for wear to crank 15s and let pressure build, then fire, rather than go from dry to 1500 RPM in a second.
I'll note that the work van has daily cycles and runs M1 all its life: 250k or so with original timing chain and only 20psi lost in compression.
The RV with 60k has very few starts, but weeks or more between.

Start-up/"cranking" wear could be obviated by a pre-oiler, and then oil could be selected just to satisfy long WOT duty. Yea/Nay?
 
working through my oil stash the Jeep will get 5W30 next - do I think that’s doing something miraculous for the motor ? - based on this site you‘d think so … but just working through the oil stash …
 
20 = thin
30 = medium
40 = thick

for 2023 … we must be more inclusive in these debates 😷
Exactly. 30=medium. Medium is good. Not too thin, not too thick, just right.
A thick euro 5W-30 weight oil with HTHS >= 3.5 is ideal. Use it in any car speced for 20 weight oil, and sleep well at night.
If CAFE didn't exist, 0W-20 wouldn't exist either.
 
The only reason I don't use the lightest wt the mfgr recommends is, if the vehicle consumes more oil that I feel it should. For instance my wifes chevy equinox. It calls for 5w30, but will use a qt of oil in 750 mies.I usally mix 5w30 with 40 or 50 wt. That will get the car between 1,000-1,250 miles. Way cheaper than doing a rebuild.,,
 
Building race engines I've seen an evolution of mechanical and fluid technology over time. Old timer oils like 20W-50, 10W-40, and even 10W-30 are fading away...which is a good thing. Toyotas can run 300k miles on "water" (as some call it) with zero issues. America is ready for 0W-8 and 0W-4.
 
When I started out in motor oil I used to be a thin guy and thought thin would be the best for Canadian cold starts.

Then I started researching euro spec oils and thought HTHS was the best measure of engine protection combined with an additive package capable of extended OCIs.

More recently I've been learning about base stocks and viscosity improves, as well as re-visiting the Motor Oil University, which is bringing me back to the thin side. So I switched sides twice on the thick vs. thin debate.
You can switch?!? 😁
 
When I was young, I was firmly in the "thick" camp. 10w-40 or 15w-40 only (the latter for the OM615 and OM617). I also believed in short oil changes. Then, 5w-40 and 0w-40 deemed acceptable. A couple years ago, after I read something about how bad 1980s 10w-40 really were in regards to HTHS, I switched over to the dark side and even used 0w-30 (still ACEA C3, so HTHS >3.5).
The weird thing is: all of these strategies did work. My MB Diesels ran great with cheap 15w-40. My Saab engines lasted well with 10w-40 and short 500km oil changes (when we had the engine of my 900 turbo open after 410000km with the exception of lightly worn rod bearings, everything was within spec for a new engine); they also refused to wear and produces excellent UOAs with 0w-40 and 0w-30 and very long oil change intervals up to 20.000km. (Easier startup and less sluggishness in cold winters with the thinner oils were, however, very noticeable.)
In the Alfa (1.9JTD 16V), I have now a 5-40 ACEA C3; on the Shelf I have two jugs of Mobil Delvac 10w-40 ESP (MB 228.51). Manual specifies either 5w-40 or 10w-40 API SJ/CF. Car is sitting in a garage, so it rarely sees cold starts below 10°C. Also Delvac is relatively cheap, so why not.
Beamer (M54B30) is on 5w-40 A3/B4.

As for the women: well, it depends. My background is in handball and rowing. I grew up around strong and tough women. That said, leightweights are prettier, but the heavies move the boat faster. So... what is your goal? I really appreciate that my wife is happy to move furniture on her own or carry 15kg of groceries back from the shop. Makes my life much easier. Conclusio: Skinny and weak is not attractive, morbidly obese neither. Fit and strong with a healthy bodyfat percentage is fine, and that range is wide.
 
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I switched to M1 0W30 AFE in the 2007 Accord k24 from 0W20 about 8 years ago. Typical use is very short trips Mon - Fri and a two hour highway trip on the weekend, with 10,000 km OCI's which has the OLM typically at 15%.

At 140,000 kms oil stays on the full mark in the winter, and drops about 1/2 litre in hot summer weather in 10,000 kms. I'll see what the top end looks like when I do the first valve adjustment in a year or so, hopefully it's staying clean.

I would run M1 0W30 ESP if I could find it in jugs on sale, instead of only expensive 1 litre bottles.
 
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None.

Lighter oils are here to stay. Your 0wXX’s are better in my opinion.

But the market has shown that thicker oils are here to stay. Thus the slow adoption of 10w30 over 15w40 in HDEO applications. 10w30 was projected to have majority market share in 2020+.

It’s barely at 15%.
That is for MPGS. Back in the 1970s straight 30 was the standard for the 4 cycle diesels and straight 40 for the 2 stroke diesels. All things equal straight viscosity oils are some what thicker under high loadings between the parts that a multi viscosity oil. Oil keeps the parts seperated.
 
I was always " just right" As thin as you can get with out loss of power and excessive racket.
I don't tolerate lost power. But I also don't like racket.

So Goldliocks "just right" for me.

Note than may cars come with oil - and spec a grade - that's just too thin.
 
Perhaps 20 years ago, I noticed on oil containers an Energy Conserving text at the bottom of the API donut.
I wondered at that time what does motor oil have to do with Fuel Economy. It should only be for protection of the engine.
Then after API SL, they limited phosphorous (anti-wear) content due to a theoretical negative effect on catalytic converters.
Then they went to low tension piston rings for fuel efficiency which did the reverse by harming the enviornment by turning engines
into oil burners that burned several quarts of oil into the air during an oil change cycle.
Now they are making oil so thin, it's thin film may allow metal on metal contact in the piston rings and bearings which heat up to 150C in most cars (even though coolant temperature stays at 100C in most cars).

In my humble opinion, we would all be better off running API SL 5W-30 A3/B4 MB 229.5 certified oil in all cars.
Average car life expectancy would be 500k miles. The way this would help the environment, is it would protect the engines so well, that no engines would be burning oil and polluting the environment (as oil burning smoke is much more polluting than burning gasoline only).
 
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