Hello all!
I am excited to see that this website is not only for Bonnevilles, but other H-body'* such as the 1997 Oldsmobile 88 that I picked up! I received this car from my uncle, who is an excellent mechanic. It has 110,000 on the body and chassis, and as of now about 200 miles on a brand new L36 3.8 V6. I love the car, it rides great. It did need a really good scrubbing, but now that that'* done, I can say that this is a good looking car despite some rear damage to the drivers side of the rear bumper. My first question on here is going to be why this H-body gets such bad gas mileage? I traded my 1988 Pontiac 6000 A-body with a 2.8 for this, and it seems that the 2.8 resembled a Toyota Corolla in fuel economy compared to this 3.8, which is comparable to the 350 in my bosses Tahoe when considering fuel economy. In any case, just wanted to say hello. I'm sure you all will be seeing me on here more often. Take care.

Welcome to the Club!

The first question I have to ask is what kind of mileage are you getting? It should be around 20 city/30highway.

It appears that I am somewhere near 20 highway, and like 14 city. I don't sit in a lot of traffic, and I don't mash the pedal at all especially since this is a brand new engine that needs to properly break in. The new motor consists of a used, re machined block (stock bore), freshened heads (the same that came with the car), new crank, new rods, pistons, timing chain, valves, etc. The intake manifold is also somewhat new (it was off the old engine but put on the new one). Lets put it this way, I have filled it up to the 3/4 mark, put about 65 miles on it (about 50 of which were highway), and the guage is halfway between 1/2 and 1/4. I know that these guages arent accurate, and vary depending upon going up or down a hill, but these measures were taken on a flat road while standing still. I might sell this thing if it doesnt do good on gas.

I am letting her break in, I'm going to give this thing a good month before I start tearing into it/selling it. I don't know about the 02 sensor(*). In fact I have a lot to learn about this L36. I am an LS1 fanatic, I have a Camaro (which currently gets better gas mileage than this thing), but am now finding out about this motor because I just go the car. Will breaking the engine in cause my mileage to get progressively better?

I will have to ask my uncle as to what 02 sensor he used. The car doesn't throw any codes, and the exhaust does not smell like gas. It runs really smooth, and has a ton of power especially up top (hit it on the freeway once), but burns a ton of gas with no symptoms of anything that could be bad.

Welcome aboard!!

Nice to see another Oldsmobile owner around.

I would like to recommend you check your gas mileage the proper way, and not use the gauge as a mileage basis, especially since as you noted, they arent always accurate.

Fill the tank up completely, I now listen for gas coming up the filler neck, because most stations I stop at seem to pump too fast for my car to handle if I use "the clicker".

Then reset your trip meter, drive around for however long you choose, refill and divide miles driven by gallons pumped. That might get you a workable figure, that might even surprise you.

I will also agree that sluggish O2 sensors are usually the biggest cause for poor mileage in a car that is otherwise running great.