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Synthetic versus regular oil and transmission fluids

My uncle, a retired airline mechanic, says there is no long term advantage to using synthetic oils. I bet him that two brand new cars driven exactly the same way for two hundred thousand miles would prove that the synthetic oiled car:

1. engine and trannie would last much longer

2 the car would get better gas mileage

WE have a huge bet. Anybody know of studies done on this to prove either one of us right or wrong?

Thanks mechanics of the world!

The type of fluids used matters far less than simply changing them at the specified intervals. Whether it lasts much longer has more to do with the owner and how the car is driven.

As for getting better gas mileage, that’s hogwash. Simply because synthetic is used doesn’t mean the engine will suddenly consume less fuel.

I’m not sure there’s any definitive way to settle this “bet” you two have on. Either car in the case you’re describing would last a very long time given the proper maintenance and driving habits. No harm is incurred using synthetic, no damage is incurred using dino oil. Take your pick.

I have not heard of a long-term blind study that would settle your bet. Even if you bought two identical cars tomorrow and drove them 20 years, the sample set would be too small to mean anything unless you agreed in advance to throw chance to the wind and let a two-car sample settle your bet.

I have driven my last two cars 275k miles on conventional oil with zero engine problems. It will take a while to beat that convincingly with synthetic oil, but who knows?

On a side-note, I KILLED the 5 speed manual transmissions in both those cars using synthetic gear oil. The problem was that the transmissions were made to use ATF, and the synthetic gear oil I put in them was heavier, around 80 weight as I recall. That was a real bad idea. It took until the second tranny failed that I got smart and figured out what was going on.

Well the car (all else being equal) will get a little better mileage with synthetics. You may not be able to measure the difference however.

As for life, there are very very few cars that die due to oil failure. They may die because someone never changed the oil or never checked to see they were very low, etc, but wear in any engine using the specified oils maintained as recommended and running under normal conditions just will not have oil related problems.

Agree that generally speaking, there will be little difference over 200,000 miles as to which oil is used. An exception would be very cold weather or very hot operation, such as trailer towing. This is where synthetic oil realy shines. Oil cnhange frequency and using the right viscosity is more imortant than whether it is synthetic.

OP seems to have a very long term bet with his uncle; hope uncle lives long enough to witness the final results.

Agree; even with today’s corrosion protection, the engine normally outlives the body, if normal maintenance is carried out. The only regions of the country with lots of engine rebuiling shops are the dry areas where cars don’t rust.

Back in my stupider days I took my '75 Civic to Aamco (Scamco) for a clutch replacement. I cranked it up to drive off the lot and it popped into gear by itself. They put gear oil in it instead of the required 10W-40.

I suppose it depends on how much you care about your car. You may just be maintaining it for the second owner, but here’s my 2?:

I’ve used synthetic oil (Mobil 1) in my car for the last 7 of the 8 years I’ve owned it.
-The engine seems quieter and smoother than on dino oil.
-Not sure about mileage–seems about the same.
-I go 6,000 miles between oil changes and the oil stays cleaner than 3,000 miles with conventional oil.
-The car seems much happier and cranks faster when the outdoor temps are <10 deg. F.
-I use a quart between 6,000 mi. oil changes with the synthetic on an engine that has 235,000 miles. I used to use 2+ quarts between 3,000 mile changes using dino oil.
-I notice no sludge buildup whatsoever under the oil cap.
-The oil changes cost about twice as much but last twice as long or better.

So it’s entirely up to you, but personally I’d never switch back to conventional oil.

There was a test done on NYC taxicabs. I read about it in consumer Reports. The results were about even between the two types of oil. No car manufacturer can make two cars in a row that are exactly the same. In general, they do a great job but nobody will ever know for sure if one car is a good one and another one is a bad one. It could be said that you are both wrong.

I sold my 1995 Civic(owned since new) in 2004 with 225,000 miles. It never had a single internal engine repair nor transmission repair. It used a pure diet of bulk conventional oil (usually 10w30) from various independent shops and dealer. I caught up with the new owner recently who has over 275k on the car now and it still has not had a single nor transmission(manual) engine problem. The car however is swiss cheese given its a New England car and the bumper is nearly falling off.

Mobil-1 claims that there is a 2% increase in gas mileage using synthetic oil. Here’s their calculator:

I believe that synthetic oils will retain their lubricating properties longer than conventional oil; that’s how they were originally marketed. By providing longer oil change intevals a fleet owner can reduce down time for each vehicle and possibly reduce the motor pool staff. If you change your oil every 3000 to 5000 miles, I doubt that you would notice a difference in engine life. BTW, Mobil does not say that Mobil-1 extends engine life (see ‘Why Synthetics?’ link at above URL).

You can also let Mobil help you decide what oil is best for you. I did that for my car and they recommended conventional motor oil for premium and superior service. Synthetic was only recommended for ultimate (highest level) service.

Aircraft mechanic ?
On airlines ?
Thats jet service almost entirely - what does his experience have to do with piston engines running unleaded fuel ?

There are a few car manufacturers who now REQUIRE synthetic lubricants. Chrysler has for years in its transmissions. VW has for years in its diesel engines, and does on its new FSI and TSI gas engines. If I remember correctly, BMW does also. In fact almost all turbo charged engines require synthetic oil due to the heat in the turbo charger. So the manufacturers and the design engineers believe that there is a benefit at times.

Check out Exxon/Mobil site for the scientific tests and results. Also, if you are going to switch to a synthetic use a true synthetic, which Mobil 1 is. It is not made from crude as are all other supposed synthetics. Mobil 1 is made from chemical combinations developed in a lab, which are explained on the site. I’m convinced synthetic Mobil 1 is best for any vehicle’s engine and transmission. I use them in all my vehicles (everyday drivers, sports car, and truck) and will not use any other lubricants. Mobil scientists are constantly improving their products. They now have “green” synthetic motor oil. Hope you win the bet.