Am I Dreaming?

[C man]

I just did a 200 mile round trip. I went to the gas station when i got home and filled back up. according to my calculations I achieved 39mpg!! It almost seems impossible. The gas hand is on the full mark and even if I add a 1/2 gallon error I still come out at 36.5mpg for the trip. I didn't run the a/c becuase its a cool day outside and I did a lot of coasting on the way back down but the land was was kind of hilly, well at least in my standards, the city I live in is pretty flat. The last trip i did I got only 25mpg round trip. This time I did replace some cracked vacuum hoses though.

What is the hightest MPG have others gotten with their 3800?

[northstar1958]

I've never gotten less than 32 mpg on road trips in my 97 pa, so i don't think your dreaming. These cars get excellent mileage for the size of the vehicle. My best ever mileage was a 600 mile trip with the wind at my back and pretty much did the same as you at 39 mpg. I live in the flatlands so maybe that helps. City driving is a solid 26+ mpg. It kills me to see the sub-compacts touting their 30mpg cars. Park avenue....Its Americas best kept secret....

Northstar

[The00Dustin]

I drive a 99 Ultra (3800 Series II Supercharged), I bought it on e-Bay with 40K miles 5 years ago and flew to FL to pick it up (I live in IN). I got 33 MPG on the first two tanks, even though half of the second tank and after that, driving 40 miles each way to work and 10 miles each way to lunch with four stops on the 40 mile legs and 1-4 stops on the 10 mile legs, I often got 28 mpg. Now with the same drive (add some sitting to one of the stops on the 40 mile legs and another possible stop on the 10 mile legs), I don't consistently get better than 25 mpg. The car has 162K on it, so I would expect some loss, but I don't even get 28 consistently when I drive 70 miles non-stop highway now, and it seems like most of that loss happened all at once sometime in the past two years, so I think something is wrong, but I don't know what.

[C man]

Well update: I was kinda of dreaming I did use a little more gas than I thought initially. I filled the gas tank at a pump were the ground slightly leaned, I usually try to avoid this but couldn't this time. I went to another gas station after a 15 mile interstate trip because the gas hand went down to fast from the full mark considering its usually routine. I realized now that I got closer to 34-36mpg which is still excellent.

Just like dustin my mileage has went down considerable. Doing my normal week city driving I use to get around 21-22mpg even in the winter (if u call it winter) and now I barely break 20mpg in the summer! On my last two trips before this one I got considerable lower mileage. Well at least one of the baffled me. The other trip I kinda now why I did worser, 3800's drink gas on acceleration.

But I did change the cracked throttle body vacuum connections and I will see If that helps. The all were brittle and cracked even the fuel pressure regulator. I also replace the connections on the EVAP system a couple of months ago. Mine was disconnected, and I noticed it by accident because it didn't cause a drive ablilty issue.

[Mag00]

Interesting, the best I've gotten with my 95 PA is 28 highway.
Then again, I usually have to go uphill at a few points...and then it slows down when you get into the city.
City driving is anywhere from 17-19...

When you coasted, did you put it in neutral?

[C man]

No I didn't put the car in neutral when I coasted. The hills weren't really step grades but more than what I'm use to. Plus I heard putting your car in neutral keeps the trans pump from pumping.

I also think that these transmission have a "coast gear" in them. I was watching a show on the discovery channel on and they were showing how transmission are built and and one of the installation steps was installing a "coasting gear" and the trans had a GM print stamp on it. I believe this because most of the cars I've driven, when u let of the gas the car losses acceleration pretty fast. In this car I can coast at least half a mile without loss of acceleration. Plus my brother drove my car one time and mentioned that it took a long time for it to slow down. I guess this is to help improve gas mileage.

Am I right on this?

[Mag00]

I was just wondering because when I coast downhill (steep hills, high speed, around 70mph) the RPM stays at 2000, and doesnt go much lower.
while in the city coasting will go down to the hundreds...

[HotZ28]

You are correct, coasting in neutral is not a good idea, in fact, it is illegal in some states. If the engine is running, the transmission pump is pumping fluid, so you don’t have to worry about fluid starvation. Any increase in fuel economy is moot, when shifting into neutral; so therefore, it is not worth the effort. You also have the issue of not being able to accelerate in the event of an emergency. In addition, coasting in neutral will diminish the engine braking effect, which leads to increased brake wear. You be the judge, pay for more frequent brake pad & rotor changes, or maybe gain .01 mpg? Remember, if you have a 2.92 final drive ratio and .70 overdrive, that is equal to 2.044 final drive ratio, so yes, the car will coast a long ways @ 55mph in OD! The best way to save fuel, is to put an egg between your foot and the accelerator pedal! Who wants a broken egg on their carpet?

[The00Dustin]

C man, just curious, but does your PA have a fuel consumption calculator? I ask because mine does, and it was accurate (I reset it at every fill up and always do the computation based on the fill up as well) up until my mileage started dropping. Since then, it is almost always high, and the higher my mileage is, the higher it is (i.e. at 25mpg it would show 25.5, but at 27mpg it would show 29). I have seen it lower than my mileage, but only in the winter if I let the car warm up for like five minutes a day (100 miles a day, fill-up every 4 days). Also, regarding coasting, my 1999 PAU definitely coasts better than my previous car (1994 LHS) ever did, and it still coasts better than a 2004 Acura RL (with shAWD) or a 2000 JEEP Grand Cherokee (in RWD), but a 2007 Cadillac CTS (with AWD) coasts just as well as my 1999 PAU (FWD). This is all with my PAU not coasting as well as it used to. Also, when coasting downhill in my PAU, I am far more likely to catch up with non-GM vehicles that aren't braking than GM vehicles that aren't braking, so while I don't know, it certainly seems to me that GM products coast better than others.

[C man]

No, I really wish I did, because I would probably drive better if I knew my instant gas mileage. I just do mine the old fashion way.

But I do have a question for HotZ28 How do you determine finial gear ratio? I've been trying to figure that out for a while.

[HotZ28]

Originally Posted by C man

But I do have a question for HotZ28 How do you determine finial gear ratio? I've been trying to figure that out for a while.

Look at the SPID sticker on the spare tire cover, if the transaxle is still OEM, it should have one of the following codes listed. There were a few others offered, but not likely in a PA.

F17 RATIO, TRANSAXLE FINAL DRIVE 2.84
FR2 RATIO, TRANSAXLE, FINAL DRIVE 2.93
F79 RATIO, TRANSAXLE, FINAL DRIVE 2.97
F83 RATIO, TRANSAXLE FINAL DRIVE 3.05
FW2 RATIO, TRANSAXLE FINAL DRIVE 3.06

[C man]

I think I have the 2.84 or maybe the 2.92 gear ratio I checked that out a while ago and kinda forgot at this point. What I don't I this

Remember, if you have a 2.92 final drive ratio and .70 overdrive, that is equal to 2.044 final drive ratio,

Doesn't the final gear ratio drive usually be the gear ratio for the first gear.
So how does that play into having a lower final gear with an overdrive gear?

And why isn't the overdrive gear considered the final gear drive ratio since its the last gear. BASICALLY I need a overview of the whole gear ratio "thing"
I've been trying to figure this one out for months. My Automotive book doesn't explain it well. This has confused me

[arcburn]

I have owned two P.Ave's and one LeSabre. I am presently driving a 2004 PA. My parents are on their second LeSabre. We consistently get 28-30 mpg on road trips (freeway etc.) Around town my wife usually gets around 24 mpg. There is something to the ability of the Buicks coasting forever.
I have always wandered why Buick has not pushed their gas mileage in advertisements. They pay a golfer 7 million a year to drive a Buick around and not one of the commercials do they state the excellent gas mileage.
The only problems I seem to have had with all of my Buicks is premature water pump failure (40,000 miles) and power door locks falling into the door panel. Both of which I repaired myself.
Several things I do that may help is. I have always used Mobile 1 10-30 synthetic and changed the transmission filter and fluid every 25,000 miles, cleaned the mass airflow sensor and the fuel injectors annually.

[ZiggyPA]

CMan which vacuum hoses did you replace?

[C man]

i really replaced the vaccum hose connectors. The one that was attached to the throttle body and the transmission modulator. It was cracked and split down the middle. I also had to replace the connector for the fuel regulator but couldn't get that at the dealership, they didn't sell it. Also I had to replace the rubber connections that when to the EVAP cansiter. It was completly disconected and broke. Gas mileage though has went down for some reason. Can't get over 19mpg in the city when I used to get 20 or 21 regardless of the season.