Anybody using synthetic oil? Help with MPG? etc.

I just traded in my 2004 Silverado with a 6.0L engine and 140,000 miles. I used it to tow a 10,000# FW in the mountains of Arizona to Montana. I replaced the factory oil with Mobile 1 full synthetic at 200 miles, then used synthetic for every oil change since then. I changed the oil based upon the Oil Sensor system. When the light came on, I changed the oil.

At 125,000, I developed a small leak over one of the rocker arm covers. I removed the cover and replaced the gasket. What was amazing was that the rocker arms and top of the cylinder head look brand new! There was no sludge what-so-ever.

I would not say I got any better gas mileage than anyone else, but I felt much more confident in the longevity of my engine when using synthetic.

I also had a 1989 Mistubishi Montero that I'd purchased new. My wife and I commuted in it over 100 miles per day. When I traded it in several years later, I had 245,000 miles on the engine and had zero work done to it other than routine timing belts per the owners manual.

I know this is anecdotal evidence, and others probably have similar results with petroleum based oils, but there was no sense in me changing from what worked.

Synthetics along with any other "additives" are nothing more than snake oil as far as MPG goes.

What many vehicle manufacturers have been doing to "help" the mileage is to spec oils which are much wider in cold to heat range. In other words now days 5W-30 or 5W-40 is the "recommended" oil specs. Older vehicles the specs were 10W-30 or 10W-40 or 15W-30, 15W-40.

The idea is the lower the oil spec the thinner the oil is when cold and this "helps" reduce the friction of the cold oil.

Where synthetics "shine" is in longevity, often can go a few miles longer on the oil changes. However the extra premium price of Synthetics sort of takes away this advantage in cost per quart..

If you are looking to "gain" mileage you have several choices... Lighten up on the go pedal OR trade your vehicle in for a "smart car".. But really there is NOTHING you can dump in your oil or gas which will increase mileage inspite of folks who make "claims" that it helps them. SAVE YOUR MONEY and don't bother with marketing gimmicks.

4 miles per hour difference for me

Why are you asking about MPG?

I tried it in both diesels I've owned.
No difference what so ever.