re: Is synthetic oil a waste?

I like it for newer engines. My old Ford 351W gets the dino oil.

Less friction = slightly better fuel economy. On my last car about 1.5mpg difference, easily documented and proven.

Also, longer oil change intervals. With Mobil 1 extended protection, they claim a 15k interval. Std Mobil 1 goes 7.5k.

Less engine wear (less friction), better fuel economy or HP (less friction), and longer change intervals at slightly higher cost (say $25 for std oil with filter, $35 for synth with filter).


Do the math comparing even a 7.5k oil change interval on synthetic vs a 3k interval on regular oil. Look at pricing (I change my own and buy when they do 'oil change specials' at Autozone and the like) and advantage of synthetic is clear IMO. The improved fuel economy is just lagniappe in this calculation.

Now, why would a mechanic who profits at the 'every 3k' oil change, tell you not to bother with synthetics that require less oil changes and likely less engine maintenance over the life of your car? ()

Hmmm....

The owner's manual in my wife's 2013 Honda specifies synthetic. The service on that car is no cost to us until June of this year.

The manufacturer of my 6 year old Silverado doesn't require, but recommends synthetic. I've always used Mobile 1 extended synthetic for that truck. 130,000 miles and I've had no trouble at all. It's supposed to go up to 15,000 miles between oil changes, but I don't usually wait that long.

A buddy of mine has a Ford F250 and swears by Amsoil. He actually changes the filter on his vehicle every 7500 miles and re-uses the oil for 15,000 mile intervals, topping it off for filter changes. I should probably mention that the diesel engine in that particular truck has had major issues, but I don't think they were related to the oil he used.

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I should probably mention that the diesel engine in that particular truck has had major issues

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He probably has a 6.0(which is in my truck) and it takes an act of congress to get it to crank in the winter. Unless you use synthetic. But I change mine every 6k

I use 5W-30 full synthetic is both trucks for the most party. Currently using M1 0W-30 in my Ranger here in PA for the extra cold weather protection. Generally use M1 or Pennzoil Platinum/Ultra for the F150 and Mobil Super Syn 5W-30 for the Ranger. Also use RP 10W-30 in my generator and power washer. Synthetics are far better for engines that can go months to years without use.

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That's some physics defying oil there.

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How so??

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Mechanics also tell you to change your oil every 3k miles. frick that noise, you can go a minimum of 5k. I use synthetic and I go about 8k between oil changes on a vehicle with 130k on it; all highway though.

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Many reports have come out that synthetic oils can go towards 10K between changes.


Here You GO.

Might just be the way I am interpreting what is said. It has a 30 viscosity at both temps. Always understood viscosity to be altered by temp.

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Redbone

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Over time 10W30 will go to a straight 30W.

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You've got it backwards. It will get thinner over time and will resemble a 10W more than a 30W. That's what happens as the oil and additive molecules get chopped up into smaller bits and as more combustion by products contaminate it.

All mult-viscosity oiis start off at the lighter weight base stocks. The additives contain molecules whose chains are more of a 'ball' shape at lower temps, thus they slide past the molecules of the base stocks relatively easy and make it keep it's low viscosity at lower temps. As the oil heats up the molecular structure of the additives open up into ribbon or string shape, which don't flow as easily past one another or the base oil molecules. Over time, and especially so in something like a motorcycle with a wet clutch and gears, the additive molecules get sheared into smaller pieces and the oil loses viscosity, not gains it.

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Synthetic oil will keep it's multi-viscosity properties much longer than non-synthetic.

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Less additives are added to synthetics due to the properties of synthetics. That's part of the reason it will go more miles.

Some oils companies, such as Lubrication Engineers, allow for 25000 oil changes with testing at intervals.

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That's not necessarily true either in every case.

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Which ones aren't and why??