Who believes they're getting worse fuel economy after switching to GC?

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Dec 25, 2002
Outside smalltown, IL
I would be one on the list. Last summer my 4Runner using my M1 5W-30 #132 mix I was getting 20-22mpg. This year I'm lucky to see 19mpg. The truck does have new tires but they are the same size as the previous set and at the same pressures. I did put new plugs in the truck since last summer but they are the identical brand and heat range. Same with the air filter. I cannot believe the oil change made all of the roughly 15% difference, but I'm becoming more convinced all the time that it did make a measurable difference... [ June 10, 2004, 05:26 PM: Message edited by: jsharp ]
M1 is on the thin side of 30 weight so if the GC is a 'thick' 30 I am not surprised. I lost 1-2 mpg going from a 5w20 to a 5w30 in my Ranger.
Are you ready for something crazier!? For the first 120K miles, I ran 5-30 (mostly mobil1, but also a batch or two of DuraBlend, Havoline dino, and Pennzoil dino). I never achieved better than 32.5, and averaged 31-32 ( I'm almost always on the freeway). Last change I switched to 15-40 Syntec (it was on clearance for $1, I couldn't pass it up [Big Grin] ). Now I'm AVERAGING 33, and my best is 35.7. I've changed nothing else on the car (ok, I'm running a different oil filter, and maybe a different brand of washer fluid [Big Grin] ). If a HEAVIER oil (both cold and hot AND HTHS) can yield better mileage, anything's possible. Dave
I ran it for close to 7,000 miles in my Audi A4 (2.8L V6). I got about 24.5-24.8 mpg with GC 0W30 and still the same mileage with BC 5W40. Also, when I ran Mobil 1 5W30 (10,000 mile interval) the previous period, I was still in the 24.7 range. So, no difference for me.
Are you sure it's the oil??? Have they changed your fuel composition? I know my Suburban gets around 16.5 mpg around New England, but when I head south and fill in Virginia that didn't have the MTBE I got over 18 mpg. Not sure the oil would make that big a difference.
At first, I SEEMED to be getting worse mileage with GC, then at 5000 miles on the oil, the Northstar took off like a jet. I changed oil shortly therafter, thinking that something happened to the oil, like it sheared or something. (sorry, no uoa) The new GC is giving me the same mileage as prior to changing it, about 27.5 HYW in an STS @ 75 mph. The only thing that changed was the oil level. I now run it at the very tip of the stick, below the "ADD" mark. Also, No more oil usage. It also does not seem to get dirty anymore. The new change has 3000 on it right now and it will probably stay in for about 8000. It's about as clean as the day I put it in.
Im at about 8500 miles into my GC run on my father's 98 Audi A6 2.8 30v. At first I thought the oil was causing my MPG to go down from about 22avg to 19, but, then I started to drive slower on the freeway, and now i am getting about 24mpg, with very little city mixed in. I used to do about 75-80 on the freeway, now i keep it at 60-70 and my milage is better. I also cleaned out the MAF sensor using electronics cleaner I got from homedepot, so this could be part of it.
Both my car and my wife's car did not lose MPG with the switch to GC. The average MPG is up slightly since the switch if anything.
I was also a little disappointed with GC (Castrol SLX A3). Fuel economy didnt seem to improve much over the previous BP Visco 7000 0w40. Even the Shell Helix Ultra 5w40 did much better.
jsharp it is probably the tires. They might be same size and at the same pressure but their rolling resistance can be quite different. As far as my experience with GC I got better milage with it then with M1 0W-20. This is even more significant since GC was in whole winter while M1 was in during the spring! GC 0W-30 26.0 mpg M1 0W-20 25.8 mpg
People should list what car they have as well as the mileage improvement vs decline. I would be willing to guess that German/European cars that call for 5-40 or a little heavier oils are getting a booost in mileage with GC, while Japanese cars for the most part that call for lighter weight oils are seeing a drop in mileage. In my 99 Civic there was a no doubt about it 3-4 mpg drop im mileage with GC.
I drive 2000 Mazda 626 with V6. It does have japanese engine! Many factors influence fuel economy: 1. gas quality 2. tires and inflation pressure 3. wheel alignment 4. spark plugs(tune up) 5. Oil But most of all is your driving speed and style.. I guess the only accurate way would be to change the oil, fill the gas tank and do a 50 or 100 mile drive at constant speed. Fill the tank again and get your MPG.... Do the sam thing with different oil but make sure that your tire pressure is the same, you use same gas station, outside temperature is the same and that you have same meal you had the day you run the previous test [Big Grin] Only then you will get to the bottom of this issue! [ June 11, 2004, 10:33 AM: Message edited by: zoomzoom ]
Lost engine responsiveness, and mileage switching from 0w-20 to 0w-30. Over 20 fillups, my average mpg dropped 2. The average temperature over this time frame was similar to the previous fill of 0w-20, as was the driving style. Since I'm trading in the car, I just switched back to a 20 wt oil, and my mileage has increased by...go figure, 2. (Only 5 fillups compared though so far)
I think zoomzoom is right But most of all is your driving speed and style.. Just by virtue of "paying attention" you'll get slightly different results. Funny how something like just making a slight change in oil visc in your car can have an effect on your right foot lol
Toyota Camry V-6, 2003.5 model (210 hp version, with variable valve timing), had tried M-1 in 5w and 10w-30, RP, and Amsoil, all with pretty consistent mileage. Put in GC at 35,000 miles, and mileage immediately dropped an average of 2-3 mpg city and highway. No other changes made. GC has been in for 2,500 miles now, no change. EDIT FOR CLARIFICATION: During this run, after noticing the mpg drop, I've dabbled with Lucas UCL and just started with FP. No changes still, but still hoping -- and watching carefully. [ June 11, 2004, 10:53 AM: Message edited by: ekpolk ]
With my 2002 Acura TL 3.2, I have lost a little on fuel economy with GC. Engine was not as responsive as compared to previous oils - RP and RL -. I have a nice little program for my PDA called -Automobile 3.1- I dont trust my math... [Big Grin] Now getting 23.4 MPG...was at 19-21 with GC. ...and 90%+ city driving. [Big Grin] 6 bottles of GC for sale.... [Big Grin] Jean
Right now I'm doing rinse with cycle rotella 15W-40 after Auto Rx-ing my engine...Had a long trip(500 miles) right after I put it in and got 28.8MPG... Next tank was my usual around the town driving...got 26.4MPG go figure..I will have 2 more tanks before my rinse cycle is done and that will give me idea what fuel economy I can expect with 40weight oil in it since I will be puting M1 0W-40 for summer.
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