Read online that if I changed my oil to synthetic in the engine AND change the gear oil to synthetic as well that I would see some improvement in gas mileage. Any thoughts on this?

I dropped a new engine in 2005, but used 87 octane @ 10.5 mpg for the first year. Starting using 92 octane,and after about one later, noticed I was getting 11.5 mpg on ave.

Is this a coincidence that I am getting better gas mileage.

Now...it has been 3years and 30,000 mile since my last tune up and now I am back to 10.5...and still using 92 octane. Could this be from it being out of tnue?

 

I have changed to synthetic oil in two of my daily drivers and have gotten about 1 to 2 miles per gallon better in both.

 

Thats's Good to here, If I could get an extra mile or two...I would gain between 37-70 miles extra per tank.

Did you also use synthetitic for your rear differenial? I alos heard that it is usefull in cold wheather (like Utah) because it is thinner.

Can any body tell me what problem I might have if I use the synthetic gear oil in moderate to warm weather environments?

 

I have not changed the rear dif oil to synthetic, yet. I have a friend that did in his '94 firehawk and his '03 cobra and he was very happy with the outcome. Synthetic oils come in the same viscocities as normal oil, so they should work just fine in temperate to warm climates. I personally like the Royal Purpal stuff.

 

You should be able to get improved fuel mileage using synthetic oils because synthetics are more "slippery" than conventional oils. This allows your engine to operate more efficiently. Amsoil also offers a performance improver that I have found to add 3 - 5 mpg and better performance in every vehicle I have used it in.

 

So....will I have to watch the gear oil levels? The synthetic being somewhat thinner...would it burn off quicker in the differential than standard gear oil?

 

Hi Rob G,

Welcome to the Chevy Forums.

The synthetics last longer.

While arguably you may see a larger MPG improvement in a smaller vehicle, I'm seeing @ .5MPG

in my crewcab, if that.

The real benefit of synthetics is longer change intervals, and up to 50%

overall less cost on lubrication changes, even with premium filters, like K&N.

 

No synthetics do not burn off faster than conventional oils. For one thing the flash point of synthetics are higher and the molecules are different. In fact you'll get up to three times more life with synthetics between changes. Amsoil offers great information sheets on drain cycle and viscosity on their website. there is also a whitepaper report detailing tests between 10 or more manufacturers posted on the site. You can check it out at Needmore Oils/AMSOIL.

 

I have made a decision that I will use synthetic gear oil and synthetic in the engine. This was a difficult decision for me as standard oils have been a mainstay for many years. It takes alot of convincing for me to change.

Its like roofing, I will not use a newer product unless it has been proven on a roof for at least 15 years.

 

Yeah, I used to feel the same way, Rob, but i just got tired of crawling under

that d@mn truck every 3,000 miles...