3.8L Grand Prix...

[Oziyak]

Hi everyone,

I'm kinda new to the board but I find it very informative and interesting.

I have 2000 Grand Prix with a 3.8L engine in it... and find that I'd much rather get better gas mileage out of it than performance.

I guess I"m wondering if any of you have worked with this enginer before (3800 Series II)... and what you would recommend to increase gas mileage.

I'm also interested in what kind of engine and/or transmission swaps I may be able to make to increase my mileage.

thanks for any comments and I'm looking foward to your comments

[reformed]

What kind of mileage are you getting now?

The best mod you can do is adjust your driving habits. I got an average of about 25mpg out of my 2005 and I didn't even really try, I just drove it lightly.

As far as an engine/trans mod, you may get lucky and find the the Buicks around your year with the 3800's in them had taller gear ratios.. I'm just guessing here, but something possibly worth looking into. Other than that, a WAI (warm air intake) and some areo mods will go a long way too. Browse around the aero section to get some ideas i.e. grill block, bellypan, wheel covers, ect.. along with upping your tire PSI to the sidewall max.. just make sure you are comfortable with that one and are aware of the fact the stopping distances can be lengthened slightly, so drive accordingly. Instrumentation is another good thing to use when driving for FE, look into a scanguage.

[Oziyak]

thanks for the reply reformed

I get about 400 km's with a mix of highway and city on a full tank $70...
which isn't that good if you ask me

I've heard of people getting over 500 km in the city with these cars


can you tell me more about this scan gauge... I"m looked it up and it looks pretty nice
I"m wondering though if it it can tell me if things like my O2 sensor may be giving me bad mileage... or if it can tell me it's reading vs. an ideal value?

thanks for the tip on the transmission.... I was hoping to maybe find a compatible 4 cylinder for the car... my current engine leaks oil... and I smell gas in the oil when I change it.. so I"m guessing teh oil rings are done.... the car is high mileage already 270,000km so I"m not surprised..

again thanks for the reply

[wagonman76]

If youve got the 4T60E transmission, Im pretty sure you can change the final drive ratio by just pulling the passenger side driveaxle and removing a small cover off the trans, and then just removing a clip. However you might have to also do a computer modification or something similar or it might detect a difference in rpm and not let your TCC lock.

[reformed]

They didn't make any 4 cylinders that would bolt in that I know of. I'm fairly certain that even if you could get one in there, the car is too heavy for it to make it worth it. The engine would probably be straining pretty hard to get all that heft up to speed.

As far as the gas smell in the oil, thats not rings, sounds like bad valve seals, or leaky injectors. Unless your car burns oil, your rings are still good. Gas is much thinner than oil and if it sits on top of the cylinders, it will find its way down into the crankcase.. leading me to believe that you have gas leaking down into your cylinders after the engine is off.

I'm not too familiar with the scangauge personally, so I'm probably not the best guy to ask.. I have one coming, so ask me again in a week. Seriously, your best bet would be to ask in the instrumentation forum, someone there, who actually owns one, can probably answer those questions better, if you don't get an answer here from someone else.

You're very welcome for the reply and welcome to ecomodder

[Oziyak]

thanks again reformed

I actually use to have an intrepid with the 2.7L in it... and the leaky valve seals in that car led to oil burning.... perhaps it's all in the design of the engine...
but you maybe right about that... and/or the leaky injector... I wonder how much gas I'm actually losing... as well as if the gas in the oil is doing any damage...?? the car leaks oil... so I'm wondering if it's the gas that actually damaged the seals... hmmm

I'm very interested to see how well I can do with this puppy.... going to have the computer reprogrammed for gas mileage soon I hope.... I'll be sure to keep everyone updated

[wagonman76]

The only 4 cylinder I can think of that might work is the 2.5 iron duke. They used them in lots of older vehicles, including a handful of early 90s Lumina sedans (also w-body but earlier design). You could probably mix and match GM parts and make one fit, but I dont think any gain would be worth it, if you even get a gain at all. If youre just putzing around town then maybe, but on the highway I think it would run out of breath way too soon.

Id see what you can do with the 3.8. Great engine, butter smooth, lots of torque, and it can do good on gas if you keep your foot out of the floor. Since you have access to computer reprogramming anyway, Id really look into bolting in a numerically lower final drive if youve got the 4T60E. There are websites that list what vehicles they are available from then go pull one from the junkyard. If it doesnt do any better, than just go back to your old one.

Good luck with whatever you do. If you find something that works well drivetrain-wise, Ive got a 3800 Trans Sport van that I might try it with.

[Zenix]

Adjusting driving habits seems to work best for me. I have a 99 gtp with a supercharged3.8L

[Ecky]

Get a scangauge and start a gas log. The instant feedback from instrumentation will be worth more than all of the mods you can do to the car itself.