has anyone measured either power gains or mpg gains before and after switching to syn oil.
my only exp was using slick 50 in the 80s and i gained 2 mpgs on a 4 cyl daily driver with no other changes.

hi

5 w 40 rotella in my 12 valve cummins and my slant 6 .

easy winter starts no kowen reason to not use it in every day drivers .

valvoline vr-1 in anything with high spring rates !

The major difference between dino and synthetic oil is that synthetic has smaller oil molecules.

https://floorjacked.com/best-synthetic-oils-explained-information-and-recommendations/

Synthetic oils will leak where petroleum oil won't on older engines

"real world experience w/synthetic oil"

1. It (Mobil1) has rather limited shelf life, it evaporates?.
2. I can't see how being in an engine would extend that.
3. The " real world" here is based on over 12 gals in 1gal/5qt plastic never opened containers, purchased in different weights, purchased at different times/stores,, stored in different indoor settings for over 3-10 years.
4. Seldom is this oddity discussed mentioned.
5. Conventional oils seem to be relatively free of this outcome

Project Farm on youtube did a fun synthetic oil showdown. The differences between a "good" vs a "bad" synthetic oil were pretty surprising. I switched over all my small engines to one of the better synthetics and on a cool or cold the day the difference in effort yanking over a pull start engine is night and day. That has to translate into cold weather mpg (not to mention engine wear) at least during warm-up. I think once the oil is up to temperature the difference is much more minimal.

There is a blog titled "MOTOR OIL ENGINEERING TEST DATA" here by a mechanical engineer wherein he tests over 250 different oils and discusses many topics.

One article is "Here is what you should follow for a successful start-up of a new rebuild of a traditional pushrod flat tappet engine.:"

Another is "STD VOLUME OIL PUMPS VS HIGH VOLUME OIL PUMPS – IS THERE REALLY A HP DIFFERENCE?"

Been driving the same daily for eight years, always synthetic oil as the manufacturer requires it. I know my car very well after 135K miles. After the factory stopped my no-charge 5-30w synthetic oil changes, I started using Mobil 1 fully synthetic 0-40. Didn't noticed any difference over the factory synthetic oil. By 100K miles my engine would burn 1 quart of oil per 7000 to 8000 miles. Then I switched to a off brand low grade 5-30w fully synthetic to save money and noticed quickly that engine would burn that 1 quart by 4000-5000 miles. I switched back to Mobil 1 0-40, and I'm back to 7000-8000 miles before I use a quart. Whether the slight weight in the two oils made the difference or the quality, I don't know. If I shop around I can get a 5 qt bottle of Mobil 1 for abt $25, not too bad considering the mileage I get from it.

Mobil 1 is available at Walmart in a 12-quart container for $49.97. That's $4.16/qt or $20.82 for 5 qts. Selection of weights may be limited.

Speaking for my own life,
do not do like I did for decades and “live in scientific sin and experimental ignorance”.

Read about Type IV SAE/TMC fuel economy tests.

If you want to know if synthetic oil makes a MPG difference “in the real world”
start by learning from the 18 wheel professional trucking companies
and “greybeards” like Claude Travis
who have thought long and deeply about how to “do this right.”

As you might guess from Type IV being in the name,
there are also Type I, Type II and Type III
Society of Automotive Engineers/Truck Maintenance Council
tests.

No it won’t.

There are also Group V base oils. And blends of Group IV and V base oils. Group III base oils are only considered synthetic here in the states. Everywhere else in the world Group III base oils are not synthetic.

He uses a gear oil test to test engine oil. Not a good way to test an engine oil. That guy has been kicked off many web sites for posting crapola.

My real world experience. Bought a new 95 Neon, after a few miles, I switched it over to Mobil1 and a Mobil1 V6 filter. That engine up until a piston broke due to something not related to oil, would go 10,000 miles and use about 1 qt. The piston broke at 450,000 miles and the two biggest things that syn did was the inside of the engine looked new, no sludge anywhere, that block could have just been washed out and reused, which I did. The other thing was that the bearings were not in serviceable condition, but within NEW limits.

It will make an air cooled engine run cooler. Noticed that after back to back to back oil changes going between Dino and syn.

For what it's worth, here's an experience I had with synthetic gear oil. I had a 68 Sweptline with 4.88's in the diff's. I was also running 38" tall tires, fresh non-synthetic gear oil and driving at a pretty high cruise speed of 75 mph. I drove to a destination about 4 hours from my house. The rear end was radiating so much heat I could not get my hand withing 2 feet of the diff cover., because it was so hot.

That high heat concerned me. When I got back home, I swapped in Redline synthetic gear oil, and made the same trip a few weeks later. After 4 hours on the freeway at 75mph, I was able to put my hand directly on the warm diff cover. The synthetic gear oil had made an amazing difference.