700 mile report on first ever use of synthetic oil

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GSDunk

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I recently became the owner of a 2003 SLT and after reading quite a few posts discussing oil changes and what is best for these 5.3 's, I decided on Mobil 1 full synthetic and a Fram synthetic oil filter.

Well after 700+ miles on the new oil, I am now completely sold on synthetic and will never use anything else ever again.

The Yukon seems to run better and better every time I drive it and with only 130000 miles on a very well maintained vehicle, the damn thing now runs like it just came off the lot and so quiet at idle that with the windows rolled up, sometimes I can't tell if the engine is even running. And just cruising at 65-70, the 5.3 is barely working up a sweat (around 2000-2100 RPMs) and is as quite and smooth as most luxury sedans.

This may be completely false, but It seems to also have an extra horse power or two.

As it was before, engine response is instant with throttle pressure but now seems just a tad quicker.

My fuel numbers have gotten slightly better and seem to be improving. The first 150 mile run I made on the new oil, I got 18.4, then I did the exact same route yesterday and got 19.7 (the route includes a few rolling hills, a small 800 foot grade and then back down the hill where 80% of the trip is on flat freeway.

With cruise control set at 67 mph on flat freeway, instant economy fluctuated between 22-24mpg. But when I set cruise to 72 mph, instant economy drops to 18-20....even though RPMs are fairly similar.

My average economy before the synthetic oil was 12.7 and now as I check it while typing this it reads 14.1

90% of my driving is city driving where the stop lights aren't timed, and each Lane on every block are covered with manholes sunk down 3-4 inches from years and years of repaving and just waiting to destroy your beautiful truck.

And if you guessed I must live in San Jose, you would be correct. Worst city streets in California.
 
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GSDunk

GSDunk

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....what kind of fuel numbers are you guys getting highway? And what is your average economy (are you light footed?...or are you addicted to the vortec power and the beautiful sound it makes at high RPM's?)
 

iamdub

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Your results are on-par with running synthetic oil. My only recommendation is to never put another Fram filter in it again. Almost any other quality name-brand filter is a safer bet than a Fram and my personal preference is Wix. Wind drag increases exponentially, not linear with speed. So, crossing a certain threshold will return increasingly drastic drops in MPG. The RPM may not be much different, but the load on the engine at that RPM is exponentially greater.
 

swathdiver

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I was a convert to Mobil 1 back in the 1980s.

One night at the drags my car was running its fastest times ever. Each run the car got faster but noticed the temp at the end of the run ticking up a little more than before. After the 5th pass, the motor was now getting hot so I pulled back into the pits and popped the hood and had a look. Like another car a few years before, the engine oil cooler line burst on the way to the track, leaving my oil out on the highway or street and not on the track. With less oil in the motor, not slapping the crank, she just kept getting quicker! Duct tape and 1 1/2 quarts allowed for the 66 mile trip home. Tore the engine down the next morning, and nothing, not a single bearing or component was hurt by it. When the line went in the other car, I used vise grips to pinch the line and filled the motor with a quart of transmission fluid to drive the 5 miles home on. That car had been running Mobil 1 as well and did not suffer internally because of the oil loss or the tranny fluid.

All those benefits you experienced can translate to just about any engine that used to run on natural oil. Regular oil is dead by 5,000 miles. No more coking and sludge when running synthetics.
 

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