i agree with tjkj. their gear oil is good but the motor oil in our engine isnt. within about 100 miles of putting it in my milage droped about 4 mpg and the overal engine performance seemed to dip a bit to.

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2003 Jeep LIberty Renegade
Rusty's Offroad 2.5in suspension lift w/ rear rancho shocks, Fastman TB, Beam's 4 point harness', custom D rings up front, Custom flowmaster exhaust, JKS Quick sway bar disco's
Hella 500's, General Grabber AT2's on stock rims with spidertrax
coming soon: Corbeau Moab seats, JBA 6"lift

Amsoil will not decrease your mileage. There are dozens of factors that can contribute to poor fuel economy, and synthetic oil isn't one of them.

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2015 Ram Ecodiesel/Big Horn/4x4/Quad Cab
2016 Arctic Fox 22G/Onboard 2500 LP Cummins Onan Generator/160 Watt Solar Panel

I took the road less traveled. Now I'm LOST.

When did you do the change? Same viscosity gear oil as before? Was it winter mix fuel during prior calculations, how many tanks did you check this on? Hows the air filter looking compared to the last series of tests? Freshness of spark plugs? Engine oil viscosity? etc, etc?

I see fluctuations all the time, one week up, next week down. Change the plugs and my mileage goes up noticeably for a while and then fluctuates. Same w/ air filter. Too many variables make up MPG readings to nail down one thing causing a change that drastic.

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99 TJ
71 C101
04 KJ
03 SFA KJ Sport
LOST JEEPS So-Cal

I have used RP in my 2006 Renegade since the first 5K miles. I now have 47K miles. I always have the oil changed between 3 & 5K miles. To date, everytime I check the oil, it is on full. That said, I have never had to add any oil. I regularly get 19-20 mpg, occasionally more with high highway miles on a tank.

At the risk of sounding like an Amsoil commercial.

I ride Harleys. I do not trailer Harleys, I ride them. They are air cooled V-Twins. Amsoil is widely accepted as the best oil for these dinosuars.

My current bike is an '07 with the 96" engine. HD has received many complaints (wusses) about excessive heat from these first-year motors. They were leaned out through the ECM for emissions reasons. Although I do not have the specs in front of me, informal testing among HD forum posters has shown a measurable decrease in engine temp. when using Amsoil.

I use Amsoil in mine & I have never been uncomfortable from the engine heat.

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LOST # 633
'05 KJ 3.7L/6spd/241 245/75/16 MT's
'88 MJ 4.0L/AW4/231 SWB HPD30 & trac-loc D44 w/3.73's
A dirty Jeep is a happy Jeep

The oil change was done about 3 weeks ago.. I do agree that there are many factors that could be in play.. but it just makes me wonder when i get a change.. My kj now has just over 18,900 miles on it.. I changed the oil to mobil at about 11,700 miles ran it for 2 weeks ( usually 600-700 miles ) then did the MPG check so at about 900-1000 total miles I got 17.2 with 5w-30... I let it run until 18,000 checked it the day before I changed to amsoil an got 17.3.. with all driving conditions the same, at 900 miles on amsoil 5w-30 I went down to 16.1 so only 3 weeks an 900 miles an I lost 1.2 MPG's??? air filter looked good, plugs aren't that old but will be changed around 20,000- 25,000 depending on when I have time to get under the hood for that.. gear oils is still stock oil at this point.. I will check it again in a couple weeks to see if it gets any better.. Please don't get me wrong I'm not saying Amsoil is bad stuff ( I had it in my '02 ram with 75,000 miles on a 4.7L and loved it ) But every MPG is important to me as I do alot of miles, an when the oil is more per quart at the counter an more costly at the pump.. I find it disapointing after hearing all the good things about it... These are just my findings in my KJ under my driving conditions, an I just wanted to give my 2 cents on the advice I had gotten from you great folks on here, an I will continue to take that advice an try it....

Don't give up on that amsoil yet. You also might notice a little oil consumption as well until your 3.7 adjusts to the new oil. Strange, but often happens when you switch to a new formula. Your mpg numbers should come back up. Also, it should give you good peace of mine that you are protecting your engine about as well as you can with the amsoil. With the rp oil, maybe not as much....supposedly sheers quickly....

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'06 3.7 sport 6 speed (long live manual tranny's)
tinted windows, cruise, midnight blue
Mopar roof rack
Royal Purple Synchromax in tranny
Royal Purple Maxgear in pumpkins
Full mopar skids, front diff collar
Future mods: Rock rails, B.F. Goodrich all terains. (In my dreams: Frankenlift)