Unexplained increase in MPG

[Craig-o]

OK, so this isn't a problem, per se, but it does have me baffled. Any thoughts would be appreciated.

On my last tank of gas, doing the same commute I've been doing for the last 3 years with this car, I got an unexpected increase in overall mileage of nearly 10%, and on the first leg of my commute, a whopping 16% increase! I do mostly freeway driving, on rolling hills, with very little stop-and-go, and typically average about 26MPG. When my DIC (reset at fill-up) showed 30.1 MPG when I rolled into work that morning, I took notice, but thought it might be because I filled up close to the freeway. But this phenominal increase held out for the entire tank - average of 28.4 MPG a 9.2% increase.

I have a bone stock - with the exception of running non-run flats - Goodyear F1 GS D3's (with 10,000 miles on them), and new AC Delco Durastop brake pads - 2001 convertible with nearly 60,000 miles on it. The pads were a recent replacement, maybe 1000 miles ago. I always run 92 octane gas, generally purchased from an independent gas station near my home - this morning I filled up at ARCO - not known for high-quality... No recent oil changes, no increased tire pressure, no new air filter, no little tweaks.

Now I'm not complaining, but something like this is noticable. If it had gone the other way, I'd be looking at making some adjustments to the ignition, airflow or exhaust, but this just baffles me.

Any insights?

 

[Bob Chadwick]

I don't even know if this would even make a difference but you are in the land of governmental control and exotic fuel mixes. Could they have changed your gasoline blend recently?

 

[Erik S. Klein]

Don't they change from a "summer blend" to a "winter blend" around here? I thought they did something like that for emissions. It does seem a bit early for the switch, though.

 

[Bob Chadwick]

I thought so to but with the prices the Government could monkey with it to try and keep the price down.

 

[Craig-o]

I think the summer/winter blend usually happens around November/December, when the increase the oxygenates to reduce something, CO2, I think. I'm sure that hasn't happened yet.

I guess I'll have to wait and see if this continues, or was just a 1-time thing.

 

[G Winter]

I have watched gas milage in my cars closely for many yrs. I have found a difference in gas from one brand-supplyer to the next. Around here we have a chain of stations called Caseys , and also used to have Texico. I would run 3 tankfulls of one and then 3 tankfuls of the other.I found that I could pay 10 cents more for the Texico over the caseys and cost the same per mile to drive, there was the much difference in the gas. Some engines like one gas better than the other.The next engine can be the reverse. Each brand has different additives.What I am getting at , you said you filled at a diff station.Do a 2 or three tank comparison. You may be surprised at the results.I have only had my 90 corvette for about two months,and am doing a comparison between about three diff supplyers to find which it like best. I already have found it does not like regular,it wants premium. Let us know how you come out.

 

[Steve Calvin]

Don't they change from a "summer blend" to a "winter blend" around here? .

They do that in the east too, but doesn't that make the mpg go down?

 

[XJ6GUY]

you say you had new pads put on?perhaps the old ones were a bit tight and created a small drag effect.

tom

 

[Patrick]

Have you switched brands of gasoline recently (ie, gone to one that contains techron)? Or maybe changed to a higher octane?

-Patrick

 

[MoeJr]

The winter blends make MPG go down. I generally lose1-2 MPG in winter.

 

[Craig-o]

The possibility of brakes dragging did cross my mind, but as I said, it was about 1000 miles ago when I changed the pads and flushed the brake fluid, so I think I would ahve noticed that sooner.

As for the differences in gasoline, that is certainly a possibility. My brother is in oil exploration for an independent company, but spent about 10 years working for Shell Oil. He told me about the "spot market" for gasoline, as with California's multiple energy woes - all of our own making, I might add - and extremely volitile gasoline market, we have had lots of opportunities to discuss this topic. Your small, independent stations buy gasoline on the spot market, basically, the excess capacity from a refinery. Since gasoline goes stale, it has a relatively short wholesale shelf life. When there's a lot of excess gas, the spot market is cheap; when there's little excess, the spot market goes through the roof. That was his explanation for why the independent's stations typically have a lower price than the branded station. It's also why the independent station has the same additives as the branded stations.

To further support this theory, I have a noon-time bike ride route that takes me past a gasoline transfer station. I see Union 76 trucks, and independent trucks filling up from the same storage tanks. Never seen Shell or Chevron trucks there, so my guess is that this is a Union 76 transfer station, and the independents are buying from 76 that day. I would expect to see them at Shell or Chevron stations as well, but can't confirm.

As such, the gas argument seems unlikely, as after 60,000 miles, I've probably filled up with gas from every supplier in California (I think there are only 3 companies with refineries in the state).

But thanks for all the thoughtful responses. Still nothing for me to grab onto, though...

Craig-o

 

[VETTEX2]

if you have seen the old movie " Pete And Tillie " you might have the answer

 

[KANE]

SURVEY SAYS-

DRIVING STYLE!!!

I have had great gas mileage and pathetic mileage. I have driven my car from Frankfurt to Berlin on a tank of gas. Its all in how you let the machine loose. Tighter reigns, less fun, more gas mileage. Looser reigns, more fun, more trips to the pump.

OK, so this isn't a problem, per se, but it does have me baffled. Any thoughts would be appreciated.

On my last tank of gas, doing the same commute I've been doing for the last 3 years with this car, I got an unexpected increase in overall mileage of nearly 10%, and on the first leg of my commute, a whopping 16% increase! I do mostly freeway driving, on rolling hills, with very little stop-and-go, and typically average about 26MPG. When my DIC (reset at fill-up) showed 30.1 MPG when I rolled into work that morning, I took notice, but thought it might be because I filled up close to the freeway. But this phenominal increase held out for the entire tank - average of 28.4 MPG a 9.2% increase.

I have a bone stock - with the exception of running non-run flats - Goodyear F1 GS D3's (with 10,000 miles on them), and new AC Delco Durastop brake pads - 2001 convertible with nearly 60,000 miles on it. The pads were a recent replacement, maybe 1000 miles ago. I always run 92 octane gas, generally purchased from an independent gas station near my home - this morning I filled up at ARCO - not known for high-quality... No recent oil changes, no increased tire pressure, no new air filter, no little tweaks.

Now I'm not complaining, but something like this is noticable. If it had gone the other way, I'd be looking at making some adjustments to the ignition, airflow or exhaust, but this just baffles me.

Any insights?

 

[tipcapman]

OK, so this isn't a problem, per se, but it does have me baffled. Any thoughts would be appreciated.

On my last tank of gas, doing the same commute I've been doing for the last 3 years with this car, I got an unexpected increase in overall mileage of nearly 10%, and on the first leg of my commute, a whopping 16% increase! I do mostly freeway driving, on rolling hills, with very little stop-and-go, and typically average about 26MPG. When my DIC (reset at fill-up) showed 30.1 MPG when I rolled into work that morning, I took notice, but thought it might be because I filled up close to the freeway. But this phenominal increase held out for the entire tank - average of 28.4 MPG a 9.2% increase.



Now I'm not complaining, but something like this is noticable. If it had gone the other way, I'd be looking at making some adjustments to the ignition, airflow or exhaust, but this just baffles me.

Any insights?

Are you quoting strictly the DIC indicated mileage? If so, you're relying on a calculated fuel consumption, not a measured fuel consumption as you would obtain if you used the gas pump figures.

I do both, and I find that if I plot a straight line through the data, it is amazingly close to a 1:1 correlation. Having said that, there are some outliers in the data, which could explain your discrepancy.

L