Will GC cause a drop in mpg?

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May 24, 2004
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Vail, Colorado
Just wondering ... My first trip with GC in the crankcase produced a 2.7 mpg drop from 29.7 mpg to 27 mpg. Car is a 2005 Subaru Outback 2.5i. The last oil fill was Mobil 1 EP 5W-30 with LC20 and VSOT. The GC is straight out of the bottle. So I wonder if it needs some break in, since the additives changed? Or, do I need to add the LC20 and VSOT to get the same benefits I had with the last fill? I remember that I thought that the LC20 and VSOT helped the M1 5W-30 get the 29.7 mpg to 32 mpg. I didn't want to mess with the GC additive pack...but a 2 mpg + loss is real money.
 
Joined
Mar 14, 2005
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Mobile, AL
There are so many variables to gas mileage that it would be impossible to determine a change in just one tank. One possible variable is a change in the gasoline from your last batch. This is the time of year that the refineries start putting out winter gas that is known to give lower fuel efficiency. Bottom line is that I don't believe that you would see a 2.7 mpg drop from just oil.
 

Thatwouldbegreat

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I knew that these points would come up before I posted. And they are valid points. But, I have two identical cars with identical mpg. So one is still at 29.7 mpg and one is now at 27 mpg. I haven't seen this much difference in mpg in the last 8500 miles, so I suspect the drop in mpg is real. My interest is why and what to do about it. I have to wonder if the LC20 / VSOT is the reason, or if the GC has lots of great qualities but fuel efficiency may not be its strong suit. There is another thread in this forum on mpg and some people reported drops in mpg, some reported no change, but I don't remember seeing any reports of improved mpg. I still looked for more GC at Autozone even after I started to wonder if GC may cost me mpg, so I'm not posting to rag on GC.
 
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Portsmouth, NH
Have you elimitated other possibilities? Do the two vehicles have the same mileage on spark plugs, and air filter? Have you made sure tire pressures have been maintained as it gets colder? Not sure about CO, but mileage does drop in New England when they change to winter gasoline forumulations. I imagine that a thicker 0w-30 could change fuel economy, however, I've noticed the same or better economy than when I was using Lubro Moly Voll Synthese 5w-40 (haven't seen a VOA for the LM, so I'm unsure what it's starting point is).
 

Thatwouldbegreat

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quote:
Have you elimitated other possibilities? Do the two vehicles have the same mileage on spark plugs, and air filter? Have you made sure tire pressures have been maintained as it gets colder?
Both cars were purchased early June, and are almost identical except for color. I only drove 275 miles so far...so I'll have to give it more time. I have driven this route with these cars so I have rough idea what is typical mileage.
 
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May 25, 2005
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Calgary Canada
I'm on my first run with GC in my BMW 3.0L inline six. I got 34MPG with mostly highway and some city driving. This is around what I would normally get with this car. I also seem to get the same number of miles per fill-up in pure city driving with GC. Bottom line....I haven't observed any difference. My car specs a thick 5w30.
 

Thatwouldbegreat

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UPDATE: Drove Vail, Co to Jackson Hole, WY after adding 4 oz LC20 and 4 pz VSOT. Mileage is exactly the same as the Outback running Mobil 1 5w-30 EP with LC20 /VSOT. Mileage on the vehicles is 9400 and 9600 miles.
 
Joined
Jan 9, 2004
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Portland, Or
My mileage dropped 3-7mpg immediately after switching from M1 0W-40 to GC in my VW 1.8T. This hasn't changed with the climate. It consistently gets lower mileage at all temperatures. I don't have an explanation for it.
 

blupupher

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Katy, Republic of Texas
No change in mileage between OEM fill, Penzoil 5w-30, Mobil Drive clean 10w-40, GC, RP 10w-30, Mobil 1 0w-30, and Havoline Syn 10w-30 in my 2004 Elantra. I have a loop I drive to and from work on weekends to get my average (105 mile trip, 55mph on cruise) and I notice a bigger difference with weather conditions than oil in the engine.
 
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Apr 13, 2004
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Washington, NJ
From what I understand, GC is a high 30 weight oil (high end of 30) while Mobil1 5w-30 is a light 30 weight oil (low end of 30). That could explain the difference in MPG.
 
Joined
Mar 8, 2005
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So Cal
I recently performed an oil change from 10w-30 Mobil 1 EP, to GC 0w-30. I really noticed a difference in the way my Tacomas 2.4l engine performs. At first, I was shocked because it sounded different and ran different...kind of like when your plugs are dirty, or when you have some issue causing the power output to be less. But, as we all know, life does not always go the way we want it to, and patience pays off here. I shrugged it off, and after a couple or three days of driving, I noticed a very pronounced change in the engine. It seemed to rev more easily, and the previous drop in perceived power output reversed. Now it seemed like its old self. I think the main reason for this is that the two oils in question are significantly different in composition. Without getting into details, I believe the Mobil EP has some moly in it as well as a few different other slick additives, where as the GC more or less relies upon a higher quality base formula to begin with. Bottom line, I wish that GC's outstanding base formula was spiced up with moly and maybe a little more calcium to reduce acidity as the oil ages. At this point though, I am quite happy as you all may remember that I have a preference for Militec-1 oil, and I always add 2 ounces of Militec per quart of oil to create an extra layer of protection between bearing and metal surfaces. Tear down several times has indicated no or inconsequential wear on all surfaces in an engine with near 280,000 miles. This engine also burns no oil and has no leaks of any kind. All cylinders have near equal pressures as a result of no ring or cylinder wall wear. Engine history...two months of break in with Valvoline full synthetic oil, the rest of the time with Castrol Syntec 10w-30 full synthetic oil up until about 10 months ago when I switched to Mobil 1 EP 10w-30 and recently back to Castrol with the Green stuff. Quite happy overall.
 
Joined
Oct 4, 2005
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Charlotte Metro area
A 2 mpg decrease on a car that was getting 30 mpg would amount to 11.75 more every 3000 miles (assuming gas costs 2.35 per gallon). SO, if GC gets you twice the mileage before you have to change it, you are coming out at least even (assuming dinosauer oil change every 3000 miles costs you about 11.75 with a Supertech filter). What? I was bored! [Roll Eyes]
 
Joined
Oct 15, 2005
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Cleveland, OH
quote:
UPDATE: Drove Vail, Co to Jackson Hole, WY after adding 4 oz LC20 and 4 pz VSOT. Mileage is exactly the same as the Outback running Mobil 1 5w-30 EP with LC20 /VSOT. Mileage on the vehicles is 9400 and 9600 miles.
Have you considered switching which Subie runs the GC? How's about a swap next OCI? If milage drops in the Subie which has consistantly gotten higher mpg AND/OR Milage in the (previously GC) Subie improves, you'll have more support for the hypothesis re: GC= lower mpg.
 
Joined
Oct 12, 2005
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Mi
Drop 2mpg? Better to stay away from GC. The best lube should provide best mpg while maintain moving park lunricated. A good API certified 5W-30 or 10W-30 is sufficnet to do so until the addictive runs out. The heat cause by high friction whether or not due to GC should avoid.
 
Joined
Aug 9, 2005
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Chicago
I recently put gold GC in my '99 Maxima, with 5oz LC, and started using FP60 for the first time. MPG w/ straight havo 5W30: 22-23 MPG w/ GC/LC/FP: high 18's. GC/LC/FP will cost me approx $125 in extra fuel consumption over the next 6k miles. If my UOA at that time isn't spectacular, I am going back to dino or ST syn. of course, my UOA on ST syn will be hard to beat, so now I'm wondering why I switched...oh that's right - ST syn is a 10W30 and my car calls for 5W. guess that means I shouldn't put the wrong oil back in!
 
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