i just changed the rear diff fluid with mobil 1 75-140w and i didn't check ahead of time and added 7oz of the lds additive. will this hurt anything? also, i've read here about running 89 octane. my problem is that all the 89 in my area has 10% ethanol. is this ok, or should i run 87 with no ethanol? thanks!

 

Most of the newer Mobil 1 bottles have the additive in them already. Last time i looked, seemed like the bottles had LT on them???
The 89oct with ethanol is better than 87oct without

 

Are you asking because the Mobil product already has the additive in it? If so, it's not a problem, I have to add 4 oz. of additive to my Grand Cherokee rear diff just to get it to make sharp turns without chirping at me even though my RP already has it in. Next time though, try it without adding extra and if you get a little chirping or ratcheting on turns, add a little until it stops. Too much can make the properties of the oil break down a little faster, but nothing catastrophic from your putting a little more in there than what you needed.

As far as the gas goes, use the 89, even though it has ethanol although it'd be nice if you could find a place has the mid grade without it.

 

the mobil 1 bottle had ls on it. i'll keep checking for the 89 without ethanol, but i live in a small town with 5 or 6 stations.

 

do you have any access to 91oct? that's what i have run since day one because it's nuttin but 10% ethanol around here and they include it in every grade including 87oct.

 

most of the 91 octane around here is ethanol free, but some of it isn't. i run that in my small engines and motorcycle. so i guess i have options

 

I'm not sure how it is on a stock tune, but I've calculated EVERY possible scenario with my SC tuner on my truck and the most efficient MPGs I get are with the 91 octane performance tune with 93 octane gas. Even when calculating the higher cost of premium fuel, my cost per mile is best with it.

You may pay more per fillup, but the gas mileage gains may equal you out or even have you slightly ahead of the game...